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Chapter 11 The Head and Neck A 58-year-old woman woke up one morning to find that the right side of her face felt “peculiar and heavy.” On looking in the mirror, she saw that the corner of her mouth on the right side was drooping and her right lower eyelid seemed to be lower than her left. When she attempted to smile, the right side of her face remained immobile and boardlike. While eating her breakfast, she noticed that her food tended to stick on the inside of her right cheek. On taking her dog for a walk, she found to her amazement that she could not whistle for his return to her side; her lips just would not pucker. When examined by her physician, she was found to have paralysis of the muscles of the entire right side of the face. She talked with a slightly slurred speech and her blood pressure was very high. To make the diagnosis, the physician had to have knowledge of the facial muscles, the laryngeal muscles, and their nerve supply. The facial paralysis, slurred speech, high blood pressure, and absence of any other abnormal findings suggested a diagnosis of a left-sided cerebral hemorrhage (stroke), secondary to high blood pressure. However, because a left-sided cerebral hemorrhage would cause paralysis of only the muscles of the lower part of the right side of the face, this was not the diagnosis. This patient had paralysis of the muscles of the entire right side of the face; this could only be caused by a lesion of the right facial nerve, which supplies the muscles. Fortunately, this patient was suffering from Bell’s palsy, the prognosis was excellent, and she had a complete recovery. P.668
Chapter Objectives

  • Head injuries from blunt trauma and penetrating missiles are associated with high mortality and severe disability. Headaches are usually caused by nonserious conditions such as sinusitis or neuralgia; however, they can represent the earliest manifestations of a life-threatening disease.
  • Facial, scalp, and mouth injuries are commonly encountered in practice and vary in seriousness from a small skin laceration to major maxillofacial trauma. Even an untreated boil on the side of the nose can be life-threatening. Facial paralysis and unequal pupils may indicate the existence of a serious neurologic deficit.
  • Many vital structures are present in the neck. Injuries or pressure on the larynx or trachea can compromise the airway. Swellings can indicate the existence of a tumor of the thyroid gland or the presence of a malignant secondary lesion in a lymph node.
  • Clearly, many signs and symptoms related to the region of the head and neck are determined by the anatomic arrangement of the various structures. This chapter discusses the basic anatomy of this complicated region and highlights the clinical relevance of the structures considered. It specifically excludes consideration of the detailed structure of the brain, which is covered in a neurology text.

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Basic Anatomy The head and neck region of the body contains many important structures compressed into a relatively small area. The Head The head is formed mainly by the skull with the brain and its covering meninges enclosed in the cranial cavity. The special senses, the eye and the ear, lie within the skull bones or in the cavities bounded by them. The brain gives rise to 12 pairs of cranial nerves, which leave the brain and pass through foramina and fissures in the skull. All the cranial nerves are distributed to structures in the head and neck, except the 10th, which also supplies structures in the chest and abdomen. Bones of the Skull Composition The skull is composed of several separate bones united at immobile joints called sutures. The connective tissue between the bones is called a sutural ligament. The mandible is an exception to this rule, for it is united to the skull by the mobile temporomandibular joint (see page 715). The bones of the skull can be divided into those of the cranium and those of the face. The vault is the upper part of the cranium, and the base of the skull is the lowest part of the cranium (Fig. 11-1). The skull bones are made up of external and internal tables of compact bone separated by a layer of spongy bone called the diploë (Fig. 11-2). The internal table is thinner and more brittle than the external table. The bones are covered on the outer and inner surfaces with periosteum. The cranium consists of the following bones, two of which are paired (Figs. 11-3 and 11-4):

  • Frontal bone: 1
  • Parietal bones: 2
  • Occipital bone: 1
  • Temporal bones: 2
  • Sphenoid bone: 1
  • Ethmoid bone: 1

The facial bones consist of the following, two of which are single:

  • Zygomatic bones: 2
  • Maxillae: 2
  • Nasal bones: 2
  • Lacrimal bones: 2
  • Vomer: 1
  • Palatine bones: 2
  • Inferior conchae: 2
  • Mandible: 1

It is unnecessary for students of medicine to know the detailed structure of each individual skull bone. However, P.670
students should be familiar with the skull as a whole and should have a dried skull available for reference as they read the following description.

Figure 11-1 Bones of the anterior aspect of the skull.

External Views of the Skull Anterior View of the Skull The frontal bone, or forehead bone, curves downward to make the upper margins of the orbits (Fig. 11-1). The superciliary arches can be seen on either side, and the supraorbital notch, or foramen, can be recognized. Medially, the frontal bone articulates with the frontal processes of the maxillae and with the nasal bones. Laterally, the frontal bone articulates with the zygomatic bone. The orbital margins are bounded by the frontal bone superiorly, the zygomatic bone laterally, the maxilla inferiorly, and the processes of the maxilla and frontal bone medially. Within the frontal bone, just above the orbital margins, are two hollow spaces lined with mucous membrane called the frontal air sinuses. These communicate with the nose and serve as voice resonators. The two nasal bones form the bridge of the nose. Their lower borders, with the maxillae, make the anterior nasal aperture. The nasal cavity is divided into two by the bony nasal septum, which is largely formed by the vomer. The superior and middle conchae are shelves of bone that project into the nasal cavity from the ethmoid on each side; the inferior conchae are separate bones. The two maxillae form the upper jaw, the anterior part of the hard palate, part of the lateral walls of the nasal cavities, and part of the floors of the orbital cavities. The two bones meet in the midline at the intermaxillary suture and form the lower margin of the nasal aperture. Below the orbit, the maxilla is perforated by the infraorbital foramen. The P.671
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alveolar process projects downward and, together with the fellow of the opposite side, forms the alveolar arch, which carries the upper teeth. Within each maxilla is a large, pyramid-shaped cavity lined with mucous membrane called the maxillary sinus. This communicates with the nasal cavity and serves as a voice resonator.

Figure 11-2 Coronal section of the upper part of the head showing the layers of the scalp, the sagittal suture of the skull, the falx cerebri, the superior and inferior sagittal venous sinuses, the arachnoid granulations, the emissary veins, and the relation of cerebral blood vessels to the subarachnoid space.
Figure 11-3 Bones of the lateral aspect of the skull.
Figure 11-4 Bones of the skull viewed from the posterior (A) and superior (B) aspects.

The zygomatic bone forms the prominence of the cheek and part of the lateral wall and floor of the orbital cavity. Medially, it articulates with the maxilla and laterally it articulates with the zygomatic process of the temporal bone to form the zygomatic arch. The zygomatic bone is perforated by two foramina for the zygomaticofacial and zygomaticotemporal nerves. The mandible, or lower jaw, consists of a horizontal body and two vertical rami (for details, see page 715). Lateral View of the Skull The frontal bone forms the anterior part of the side of the skull and articulates with the parietal bone at the coronal suture (Fig. 11-3). The parietal bones form the sides and roof of the cranium and articulate with each other in the midline at the sagittal suture. They articulate with the occipital bone behind, at the lambdoid suture. The skull is completed at the side by the squamous part of the occipital bone; parts of the temporal bone, namely, the squamous, tympanic, mastoid process, styloid process, and zygomatic process; and the greater wing of the sphenoid. Note the position of the external auditory meatus. The ramus and body of the mandible lie inferiorly. Note that the thinnest part of the lateral wall of the skull is where the anteroinferior corner of the parietal bone articulates with the greater wing of the sphenoid; this point is referred to as the pterion. Clinically, the pterion is an important area because it overlies the anterior division of the middle meningeal artery and vein. Identify the superior and inferior temporal lines, which begin as a single line from the posterior margin of the zygomatic process of the frontal bone and diverge as they arch backward. The temporal fossa lies below the inferior temporal line. The infratemporal fossa lies below the infratemporal crest on the greater wing of the sphenoid. The pterygomaxillary fissure is a vertical fissure that lies within the fossa between the pterygoid process of the sphenoid bone and back of the maxilla. It leads medially into the pterygopalatine fossa. The inferior orbital fissure is a horizontal fissure between the greater wing of the sphenoid bone and the maxilla. It leads forward into the orbit. The pterygopalatine fossa is a small space behind and below the orbital cavity. It communicates laterally with the infratemporal fossa through the pterygomaxillary fissure, medially with the nasal cavity through the sphenopalatine foramen, superiorly with the skull through the foramen rotundum, and anteriorly with the orbit through the inferior orbital fissure. Posterior View of the Skull The posterior parts of the two parietal bones (Fig. 11-4) with the intervening sagittal suture are seen above. Below, the parietal bones articulate with the squamous part of the occipital bone at the lambdoid suture. On each side the occipital bone articulates with the temporal bone. In the midline of the occipital bone is a roughened elevation called the external occipital protuberance, which gives attachment to muscles and the ligamentum nuchae. On either side of the protuberance the superior nuchal lines extend laterally toward the temporal bone. Superior View of the Skull Anteriorly, the frontal bone (Fig. 11-4) articulates with the two parietal bones at the coronal suture. Occasionally, the two halves of the frontal bone fail to fuse, leaving a midline metopic suture. Behind, the two parietal bones articulate in the midline at the sagittal suture. Inferior View of the Skull If the mandible is discarded, the anterior part of this aspect of the skull is seen to be formed by the hard palate (Fig. 11-5). The palatal processes of the maxillae and the horizontal plates of the palatine bones can be identified. In the midline anteriorly is the incisive fossa and foramen. Posterolaterally are the greater and lesser palatine foramina. Above the posterior edge of the hard palate are the choanae (posterior nasal apertures). These are separated from each other by the posterior margin of the vomer and are bounded laterally by the medial pterygoid plates of the sphenoid bone. The inferior end of the medial pterygoid plate is prolonged as a curved spike of bone, the pterygoid hamulus. Posterolateral to the lateral pterygoid plate, the greater wing of the sphenoid is pierced by the large foramen ovale and the small foramen spinosum. Posterolateral to the foramen spinosum is the spine of the sphenoid. Behind the spine of the sphenoid, in the interval between the greater wing of the sphenoid and the petrous part of the temporal bone, is a groove for the cartilaginous part of the auditory tube. The opening of the bony part of the tube can be identified. The mandibular fossa of the temporal bone and the articular tubercle form the upper articular surfaces for the temporomandibular joint. Separating the mandibular fossa from the tympanic plate posteriorly is the squamotympanic fissure, through the medial end of which the chorda tympani nerve exits from the tympanic cavity. The styloid process of the temporal bone projects downward and forward from its inferior aspect. The opening of the carotid canal can be seen on the inferior surface of the petrous part of the temporal bone. The medial end of the petrous part of the temporal bone is irregular and, together with the basilar part of the occipital bone and the greater wing of the sphenoid, forms the foramen lacerum. During life, the foramen lacerum is closed with fibrous tissue, and only a few small vessels pass through this foramen from the cavity of the skull to the exterior. The tympanic plate, which forms part of the temporal bone, is C shaped on section and forms the bony part of the external auditory meatus. While examining this region, identify the suprameatal crest on the lateral surface of the squamous part of the temporal bone, the suprameatal triangle, and the suprameatal spine. P.674

Figure 11-5 Inferior surface of the base of the skull.

In the interval between the styloid and mastoid processes, the stylomastoid foramen can be seen. Medial to the styloid process, the petrous part of the temporal bone has a deep notch, which, together with a shallower notch on the occipital bone, forms the jugular foramen. Behind the posterior apertures of the nose and in front of the foramen magnum are the sphenoid bone and the basilar part of the occipital bone. The pharyngeal tubercle is a small prominence on the undersurface of the basilar part of the occipital bone in the midline. The occipital condyles should be identified; they articulate with the superior aspect of the lateral mass of the first cervical vertebra, the atlas. Superior to the occipital condyle is the hypoglossal canal for transmission of the hypoglossal nerve (Fig. 11-6). Posterior to the foramen magnum in the midline is the external occipital protuberance. The superior nuchal lines should be identified as they curve laterally on each side. The Cranial Cavity The cranial cavity contains the brain and its surrounding meninges, portions of the cranial nerves, arteries, veins, and venous sinuses. Vault of the Skull The internal surface of the vault shows the coronal, sagittal, and lambdoid sutures. In the midline is a shallow sagittal groove that lodges the superior sagittal sinus. On each side of the groove are several small pits, called granular pits, P.675
which lodge the lateral lacunae and arachnoid granulations (see page 683). Several narrow grooves are present for the anterior and posterior divisions of the middle meningeal vessels as they pass up the side of the skull to the vault.

Figure 11-6 Internal surface of the base of the skull.

Base of the Skull The interior of the base of the skull (Fig. 11-6) is divided into three cranial fossae: anterior, middle, and posterior. The anterior cranial fossa is separated from the middle cranial fossa by the lesser wing of the sphenoid, and the middle cranial fossa is separated from the posterior cranial fossa by the petrous part of the temporal bone. Anterior Cranial Fossa The anterior cranial fossa lodges the frontal lobes of the cerebral hemispheres. It is bounded anteriorly by the inner surface of the frontal bone, and in the midline is a crest for the attachment of the falx cerebri. Its posterior boundary is the sharp lesser wing of the sphenoid, which articulates laterally with the frontal bone and meets the anteroinferior angle of the parietal bone, or the pterion. The medial end of the lesser wing of the sphenoid forms the anterior clinoid process on each side, which gives attachment to the tentorium cerebelli. The median part of the anterior cranial fossa is limited posteriorly by the groove for the optic chiasma. The floor of the fossa is formed by the ridged orbital plates of the frontal bone laterally and by the cribriform plate of the ethmoid medially (Fig. 11-6). The crista galli is a sharp upward projection of the ethmoid bone in the midline for the attachment of the falx cerebri. Alongside the crista galli is a narrow slit in the cribriform plate for the passage of the anterior ethmoidal nerve into the nasal cavity. The upper surface of the cribriform plate supports the olfactory bulbs, and the small perforations in the cribriform plate are for the olfactory nerves. Middle Cranial Fossa The middle cranial fossa consists of a small median part and expanded lateral parts (Fig. 11-6). The median raised part is P.676
formed by the body of the sphenoid, and the expanded lateral parts form concavities on either side, which lodge the temporal lobes of the cerebral hemispheres. It is bounded anteriorly by the lesser wings of the sphenoid and posteriorly by the superior borders of the petrous parts of the temporal bones. Laterally lie the squamous parts of the temporal bones, the greater wings of the sphenoid, and the parietal bones. The floor of each lateral part of the middle cranial fossa is formed by the greater wing of the sphenoid and the squamous and petrous parts of the temporal bone. The sphenoid bone resembles a bat having a centrally placed body with greater and lesser wings that are outstretched on each side. The body of the sphenoid contains the sphenoid air sinuses, which are lined with mucous membrane and communicate with the nasal cavity; they serve as voice resonators. Anteriorly, the optic canal transmits the optic nerve and the ophthalmic artery, a branch of the internal carotid artery, to the orbit. The superior orbital fissure, which is a slitlike opening between the lesser and greater wings of the sphenoid, transmits the lacrimal, frontal, trochlear, oculomotor, nasociliary, and abducent nerves, together with the superior ophthalmic vein. The sphenoparietal venous sinus runs medially along the posterior border of the lesser wing of the sphenoid and drains into the cavernous sinus. The foramen rotundum, which is situated behind the medial end of the superior orbital fissure, perforates the greater wing of the sphenoid and transmits the maxillary nerve from the trigeminal ganglion to the pterygopalatine fossa. The foramen ovale lies posterolateral to the foramen rotundum (Fig. 11-6). It perforates the greater wing of the sphenoid and transmits the large sensory root and small motor root of the mandibular nerve to the infratemporal fossa; the lesser petrosal nerve also passes through it. The small foramen spinosum lies posterolateral to the foramen ovale and also perforates the greater wing of the sphenoid. The foramen transmits the middle meningeal artery from the infratemporal fossa (see page 750) into the cranial cavity. The artery then runs forward and laterally in a groove on the upper surface of the squamous part of the temporal bone and the greater wing of the sphenoid (Fig. 11-20). After a short distance, the artery divides into anterior and posterior branches. The anterior branch passes forward and upward to the anteroinferior angle of the parietal bone (Fig. 11-131A). Here, the bone is deeply grooved or tunneled by the artery for a short distance before it runs backward and upward on the parietal bone. It is at this site that the artery may be damaged after a blow to the side of the head. The posterior branch passes backward and upward across the squamous part of the temporal bone to reach the parietal bone. The large and irregularly shaped foramen lacerum lies between the apex of the petrous part of the temporal bone and the sphenoid bone (Fig. 11-6). The inferior opening of the foramen lacerum in life is filled by cartilage and fibrous tissue, and only small blood vessels pass through this tissue from the cranial cavity to the neck. The carotid canal opens into the side of the foramen lacerum above the closed inferior opening. The internal carotid artery enters the foramen through the carotid canal and immediately turns upward to reach the side of the body of the sphenoid bone. Here, the artery turns forward in the cavernous sinus to reach the region of the anterior clinoid process. At this point, the internal carotid artery turns vertically upward, medial (Fig. 11-20) to the anterior clinoid process, and emerges from the cavernous sinus (see page 750). Lateral to the foramen lacerum is an impression on the apex of the petrous part of the temporal bone for the trigeminal ganglion. On the anterior surface of the petrous bone are two grooves for nerves; the largest medial groove is for the greater petrosal nerve, a branch of the facial nerve; the smaller lateral groove is for the lesser petrosal nerve, a branch of the tympanic plexus. The greater petrosal nerve enters the foramen lacerum deep to the trigeminal ganglion and joins the deep petrosal nerve (sympathetic fibers from around the internal carotid artery), to form the nerve of the pterygoid canal. The lesser petrosal nerve passes forward to the foramen ovale. The abducent nerve bends sharply forward across the apex of the petrous bone, medial to the trigeminal ganglion. Here, it leaves the posterior cranial fossa and enters the cavernous sinus. The arcuate eminence is a rounded eminence found on the anterior surface of the petrous bone and is caused by the underlying superior semicircular canal. The tegmen tympani, a thin plate of bone, is a forward extension of the petrous part of the temporal bone and adjoins the squamous part of the bone (Fig. 11-6). From behind forward, it forms the roof of the mastoid antrum, the tympanic cavity, and the auditory tube. This thin plate of bone is the only major barrier that separates infection in the tympanic cavity from the temporal lobe of the cerebral hemisphere (Fig. 11-30). The median part of the middle cranial fossa is formed by the body of the sphenoid bone (Fig. 11-6). In front is the sulcus chiasmatis, which is related to the optic chiasma and leads laterally to the optic canal on each side. Posterior to the sulcus is an elevation, the tuberculum sellae. Behind the elevation is a deep depression, the sella turcica, which lodges the pituitary gland. The sella turcica is bounded posteriorly by a square plate of bone called the dorsum sellae. The superior angles of the dorsum sellae have two tubercles, called the posterior clinoid processes, which give attachment to the fixed margin of the tentorium cerebelli. The cavernous sinus is directly related to the side of the body of the sphenoid (Figs. 11-9 and 11-10). It carries in its lateral wall the third and fourth cranial nerves and the ophthalmic and maxillary divisions of the fifth cranial nerve (Fig. 11-12). The internal carotid artery and the sixth cranial nerve pass forward through the sinus. Posterior Cranial Fossa The posterior cranial fossa is deep and lodges the parts of the hindbrain, namely, the cerebellum, pons, and medulla oblongata. Anteriorly the fossa is bounded by the superior border of the petrous part of the temporal bone, and posteriorly it is bounded by the internal surface of the squamous part of the occipital bone (Fig. 11-6). The floor of the posterior fossa is formed by the basilar, condylar, and squamous parts of the occipital bone and the mastoid part of the temporal bone. P.677
The roof of the fossa is formed by a fold of dura, the tentorium cerebelli, which intervenes between the cerebellum below and the occipital lobes of the cerebral hemispheres above (Fig. 11-10). The foramen magnum occupies the central area of the floor and transmits the medulla oblongata and its surrounding meninges, the ascending spinal parts of the accessory nerves, and the two vertebral arteries. The hypoglossal canal is situated above the anterolateral boundary of the foramen magnum (Fig. 11-6) and transmits the hypoglossal nerve. The jugular foramen lies between the lower border of the petrous part of the temporal bone and the condylar part of the occipital bone. It transmits the following structures from before backward: the inferior petrosal sinus; the 9th, 10th, and 11th cranial nerves; and the large sigmoid sinus. The inferior petrosal sinus descends in the groove on the lower border of the petrous part of the temporal bone to reach the foramen. The sigmoid sinus turns down through the foramen to become the internal jugular vein. The internal acoustic meatus pierces the posterior surface of the petrous part of the temporal bone. It transmits the vestibulocochlear nerve and the motor and sensory roots of the facial nerve. The internal occipital crest runs upward in the midline posteriorly from the foramen magnum to the internal occipital protuberance; to it is attached the small falx cerebelli over the occipital sinus. On each side of the internal occipital protuberance is a wide groove for the transverse sinus (Fig. 11-6). This groove sweeps around on either side, on the internal surface of the occipital bone, to reach the posteroinferior angle or corner of the parietal bone. The groove now passes onto the mastoid part of the temporal bone, and here the transverse sinus becomes the sigmoid sinus. The superior petrosal sinus runs backward along the upper border of the petrous bone in a narrow groove and drains into the sigmoid sinus. As the sigmoid sinus descends to the jugular foramen, it deeply grooves the back of the petrous bone and the mastoid part of the temporal bone. Here, it lies directly posterior to the mastoid antrum.

Table 11-1 Summary of the More Important Openings in the Base of the Skull and the Structures That Pass Through Them
Opening in Skull Bone of Skull Structures Transmitted
Anterior Cranial Fossa
Perforations in cribriform plate Ethmoid Olfactory nerves
Middle Cranial Fossa
Optic canal Lesser wing of sphenoid Optic nerve, ophthalmic artery
Superior orbital fissure Between lesser and greater wings of sphenoid Lacrimal, frontal, trochlear, oculomotor, nasociliary, and abducent nerves; superior ophthalmic vein
Foramen rotundum Greater wing of sphenoid Maxillary division of the trigeminal nerve
Foramen ovale Greater wing of sphenoid Mandibular division of the trigeminal nerve, lesser petrosal nerve
Foramen spinosum Greater wing of sphenoid Middle meningeal artery
Foramen lacerum Between petrous part of temporal and sphenoid Internal carotid artery
Posterior Cranial Fossa
Foramen magnum Occipital Medulla oblongata, spinal part of accessory nerve, and right and left vertebral arteries
Hypoglossal canal Occipital Hypoglossal nerve
Jugular foramen Between petrous part of temporal and condylar part of occipital Glossopharyngeal, vagus, and accessory nerves; sigmoid sinus becomes internal jugular vein
Internal acoustic meatus Petrous part of temporal Vestibulocochlear and facial nerves

Table 11-1 provides a summary of the more important openings in the base of the skull and the structures that pass through them. Neonatal Skull The newborn skull (Fig. 11-8), compared with the adult skull, has a disproportionately large cranium relative to the face. In childhood, the growth of the mandible, the maxillary sinuses, and the alveolar processes of the maxillae results in a great increase in length of the face. The bones of the skull are smooth and unilaminar, there being no diploë present. Most of the skull bones are ossified at birth, but the process is incomplete, and the bones are mobile on each other, being connected by fibrous tissue or cartilage. The bones of the vault are ossified in membrane; the bones of the base are ossified in cartilage. The bones of the vault are not closely knit at sutures, as in the adult, but are separated by unossified membranous intervals called P.678
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fontanelles. Clinically, the anterior and posterior fontanelles are most important and are easily examined in the midline of the vault. Clinical Notes Fractures of the Skull Fractures of the skull are common in the adult but much less so in the young child. In the infant skull, the bones are more resilient than in the adult skull, and they are separated by fibrous sutural ligaments. In the adult, the inner table of the skull is particularly brittle. Moreover, the sutural ligaments begin to ossify during middle age. The type of fracture that occurs in the skull depends on the age of the patient, the severity of the blow, and the area of skull receiving the trauma. The adult skull may be likened to an eggshell in that it possesses a certain limited resilience beyond which it splinters. A severe, localized blow produces a local indentation, often accompanied by splintering of the bone. Blows to the vault often result in a series of linear fractures, which radiate out through the thin areas of bone. The petrous parts of the temporal bones and the occipital crests strongly reinforce the base of the skull and tend to deflect linear fractures. In the young child, the skull may be likened to a table-tennis ball in that a localized blow produces a depression without splintering. This common type of circumscribed lesion is referred to as a “pond” fracture. Fractures of the Anterior Cranial Fossa In fractures of the anterior cranial fossa, the cribriform plate of the ethmoid bone may be damaged. This usually results in tearing of the overlying meninges and underlying mucoperiosteum. The patient will have bleeding from the nose (epistaxis) and leakage of cerebrospinal fluid into the nose (cerebrospinal rhinorrhea). Fractures involving the orbital plate of the frontal bone result in hemorrhage beneath the conjunctiva and into the orbital cavity, causing exophthalmos. The frontal air sinus may be involved, with hemorrhage into the nose. Fractures of the Middle Cranial Fossa Fractures of the middle cranial fossa are common, because this is the weakest part of the base of the skull. Anatomically, this weakness is caused by the presence of numerous foramina and canals in this region; the cavities of the middle ear and the sphenoidal air sinuses are particularly vulnerable. The leakage of cerebrospinal fluid and blood from the external auditory meatus is common. The seventh and eighth cranial nerves may be involved as they pass through the petrous part of the temporal bone. The third, fourth, and sixth cranial nerves may be damaged if the lateral wall of the cavernous sinus is torn. Blood and cerebrospinal fluid may leak into the sphenoidal air sinuses and then into the nose. Fractures of the Posterior Cranial Fossa In fractures of the posterior cranial fossa, blood may escape into the nape of the neck deep to the postvertebral muscles. Some days later, it tracks between the muscles and appears in the posterior triangle, close to the mastoid process. The mucous membrane of the roof of the nasopharynx may be torn, and blood may escape there. In fractures involving the jugular foramen, the 9th, 10th, and 11th cranial nerves may be damaged. The strong bony walls of the hypoglossal canal usually protect the hypoglossal nerve from injury. Fractures of Facial Bones Bone Injuries and Skeletal Development The developing bones of a child’s face are more pliable than an adult’s, and fractures may be incomplete or greenstick. In adults, the presence of well-developed, air-filled sinuses and the mucoperiosteal surfaces of the alveolar parts of the upper and lower jaws means that most facial fractures should be considered to be open fractures, susceptible to infection, and requiring antibiotic therapy. Anatomy of Common Facial Fractures Automobile accidents, fisticuffs, and falls are common causes of facial fractures. Fortunately, the upper part of the skull is developed from membrane (whereas the remainder is developed from cartilage); therefore, this part of the skull in children is relatively flexible and can absorb considerable force without resulting in a fracture. Signs of fractures of the facial bones include deformity, ocular displacement, or abnormal movement accompanied by crepitation and malocclusion of the teeth. Anesthesia or paresthesia of the facial skin will follow fracture of bones through which branches of the trigeminal nerve pass to the skin. The muscles of the face are thin and weak and cause little displacement of the bone fragments. Once a fracture of the maxilla has been reduced, for example, prolonged fixation is not needed. However, in the case of the mandible, the strong muscles of mastication can create considerable displacement, requiring long periods of fixation. The most common facial fractures involve the nasal bones, followed by the zygomatic bone and then the mandible. To fracture the maxillary bones and the supraorbital ridges of the frontal bones, an enormous force is required. Nasal Fractures Fractures of the nasal bones, because of the prominence of the nose, are the most common facial fractures. Because the bones are lined with mucoperiosteum, the fracture is considered open; the overlying skin may also be lacerated. Although most are simple fractures and are reduced under local anesthesia, some are associated with severe injuries to the nasal septum and require careful treatment under general anesthesia. Maxillofacial Fractures Maxillofacial fractures usually occur as the result of massive facial trauma. There is extensive facial swelling, midface mobility of the underlying bone on palpation, malocclusion of the teeth with anterior open bite, and possibly leakage of cerebrospinal fluid (cerebrospinal rhinorrhea) secondary to fracture of the cribriform plate of the ethmoid bone. Double vision (diplopia) may be present, owing to orbital wall damage. Involvement of the infraorbital nerve with anesthesia or paresthesia of the skin of the cheek and upper gum may occur in fractures of the body of the maxilla. Nose bleeding may also occur in maxillary fractures. Blood enters the maxillary air sinus and then leaks into the nasal cavity. The sites of the fractures were classified by Le Fort as type I, II, or III; these fractures are summarized in Figure 11-7. Blowout Fractures of the Maxilla A severe blow to the orbit (as from a baseball) may cause the contents of the orbital cavity to explode downward through the floor of the orbit into the maxillary sinus. Damage to the infraorbital nerve, resulting in altered sensation to the skin of the cheek, upper lip, and gum, may occur. Fractures of the Zygoma or Zygomatic Arch The zygoma or zygomatic arch can be fractured by a blow to the side of the face. Although it can occur as an isolated fracture, as from a blow from a clenched fist, it may be associated with multiple other fractures of the face, as often seen in automobile accidents.

Figure 11-7 Le Fort classification of maxillofacial fractures. The red line denotes the fracture line.

The anterior fontanelle is diamond shaped and lies between the two halves of the frontal bone in front and the two parietal bones behind (Fig. 11-8). The fibrous membrane forming the floor of the anterior fontanelle is replaced by bone and is closed by 18 months of age. The posterior fontanelle is triangular and lies between the two parietal bones in front and the occipital bone behind. By the end of the first year, the fontanelle is usually closed and can no longer be palpated. The tympanic part of the temporal bone is merely a C-shaped ring at birth, compared with a C-shaped curved plate in the adult. This means that the external auditory meatus is almost entirely cartilaginous in the newborn, and the tympanic membrane is nearer the surface. Although the tympanic membrane is nearly as large as in the adult, it faces more inferiorly. During childhood the tympanic plate grows laterally, forming the bony part of the meatus, and the tympanic membrane comes to face more directly laterally. The mastoid process is not present at birth (Fig. 11-8) and develops later in response to the pull of the sternocleidomastoid muscle when the child moves his or her head. At birth, the mastoid antrum lies about 3 mm deep to the floor of the suprameatal triangle. As growth of the skull continues, the lateral bony wall thickens so that at puberty the antrum may lie as much as 15 mm from the surface. The mandible has right and left halves at birth, united in the midline with fibrous tissue. The two halves fuse at the symphysis menti by the end of the first year. The angle of the mandible at birth is obtuse (Fig. 11-8), the head being placed level with the upper margin of the body and the coronoid process lying at a superior level to the head. It is only after eruption of the permanent teeth that the angle of the mandible assumes the adult shape and the head and neck grow so that the head comes to lie higher than the coronoid process. In old age, the size of the mandible is reduced when the teeth are lost. As the alveolar part of the bone becomes smaller, the ramus becomes oblique in position so that the head is bent posteriorly. P.680
Clinical Notes Clinical Features of the Neonatal Skull Fontanelles Palpation of the fontanelles enables the physician to determine the progress of growth in the surrounding bones, the degree of hydration of the baby (e.g., if the fontanelles are depressed below the surface, the baby is dehydrated), and the state of the intracranial pressure (a bulging fontanelle indicates raised intracranial pressure). Samples of cerebrospinal fluid can be obtained by passing a long needle obliquely through the anterior fontanelle into the subarachnoid space or even into the lateral ventricle. Clinically, it is usually not possible to palpate the anterior fontanelle after 18 months, because the frontal and parietal bones have enlarged to close the gap. Tympanic Membrane At birth, the tympanic membrane faces more downward and less laterally than in maturity; when examined with the otoscope it therefore lies more obliquely in the infant than in the adult. Forceps Delivery and the Facial Nerve In the newborn infant, the mastoid process is not developed, and the facial nerve, as it emerges from the stylomastoid foramen, is close to the surface. Thus, it can be damaged by forceps in a difficult delivery.

Figure 11-8 Neonatal skull as seen from the anterior (A) and lateral (B) aspects.

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Figure 11-9 Interior of the skull showing the dura mater and its contained venous sinuses. Note the connections of the veins of the scalp and the veins of the face with the venous sinuses.

The Meninges The brain in the skull is surrounded by three protective membranes, or meninges: the dura mater, the arachnoid mater, and the pia mater. (The spinal cord in the vertebral column is also surrounded by three meninges. See page 871.) Dura Mater of the Brain The dura mater is conventionally described as two layers: the endosteal layer and the meningeal layer (Fig. 11-2). These are closely united except along certain lines, where they separate to form venous sinuses. The endosteal layer is nothing more than the ordinary periosteum covering the inner surface of the skull bones. It does not extend through the foramen magnum to become continuous with the dura mater of the spinal cord. Around the margins of all the foramina in the skull it becomes continuous with the periosteum on the outside of the skull bones. At the sutures it is continuous with the sutural ligaments. It is most strongly adherent to the bones over the base of the skull. The meningeal layer is the dura mater proper. It is a dense, strong, fibrous membrane covering the brain and is continuous through the foramen magnum with the dura mater of the spinal cord. It provides tubular sheaths for the cranial nerves as the latter pass through the foramina in the skull. Outside the skull the sheaths fuse with the epineurium of the nerves. The meningeal layer sends inward four septa that divide the cranial cavity into freely communicating spaces lodging the subdivisions of the brain. The function of these septa is to restrict the rotatory displacement of the brain. The falx cerebri is a sickle-shaped fold of dura mater that lies in the midline between the two cerebral hemispheres (Figs. 11-9 and 11-13). Its narrow end in front is attached to the internal frontal crest and the crista galli. Its broad posterior part blends in the midline with the upper surface of the tentorium cerebelli. The superior sagittal sinus runs in its upper fixed margin, the inferior sagittal sinus runs in its lower concave free margin, and the straight sinus runs along its attachment to the tentorium cerebelli. The tentorium cerebelli is a crescent-shaped fold of dura mater that roofs over the posterior cranial fossa (Figs. 11-9, 11-10, and 11-11). It covers the upper surface of the cerebellum and supports the occipital lobes of the cerebral hemispheres. In front is a gap, the tentorial notch, for the P.682
passage of the midbrain (Figs. 11-11 and 11-12), thus producing an inner free border and an outer attached or fixed border. The fixed border is attached to the posterior clinoid processes, the superior borders of the petrous bones, and the margins of the grooves for the transverse sinuses on the occipital bone. The free border runs forward at its two ends, crosses the attached border, and is affixed to the anterior clinoid process on each side. At the point where the two borders cross, the third and fourth cranial nerves pass forward to enter the lateral wall of the cavernous sinus (Figs. 11-11 and 11-12).

Figure 11-10 Diaphragma sellae and tentorium cerebelli. Note the position of the venous sinuses.

Close to the apex of the petrous part of the temporal bone, the lower layer of the tentorium is pouched forward beneath the superior petrosal sinus to form a recess for the trigeminal nerve and the trigeminal ganglion (Fig. 11-11). The falx cerebri and the falx cerebelli are attached to the upper and lower surfaces of the tentorium, respectively. The straight sinus runs along its attachment to the falx cerebri, the superior petrosal sinus along its attachment to the petrous bone, and the transverse sinus along its attachment to the occipital bone (Fig. 11-10). The falx cerebelli is a small, sickle-shaped fold of dura mater that is attached to the internal occipital crest and projects forward between the two cerebellar hemispheres. Its posterior fixed margin contains the occipital sinus. The diaphragma sellae is a small circular fold of dura mater that forms the roof for the sella turcica (Fig. 11-6). A small opening in its center allows passage of the stalk of the pituitary gland (Fig. 11-12). Dural Nerve Supply Branches of the trigeminal, vagus, and first three cervical nerves and branches from the sympathetic system pass to the dura. Numerous sensory endings are in the dura. The dura is sensitive to stretching, which produces the sensation of headache. Stimulation of the sensory endings of the trigeminal nerve above the level of the tentorium cerebelli produces referred pain to an area of skin on the same side of the head. Stimulation of the dural endings below the level of the tentorium produces referred pain to the back of the neck and back of the scalp along the distribution of the greater occipital nerve. Dural Arterial Supply Numerous arteries supply the dura mater from the internal carotid, maxillary, ascending pharyngeal, occipital, and P.683
vertebral arteries. From a clinical standpoint, the most important is the middle meningeal artery, which is commonly damaged in head injuries.

Figure 11-11 Lateral view of the skull showing the falx cerebri, tentorium cerebelli, brainstem, and trigeminal ganglion.

The middle meningeal artery arises from the maxillary artery in the infratemporal fossa (see page 750). It enters the cranial cavity and runs forward and laterally in a groove on the upper surface of the squamous part of the temporal bone (Fig. 11-20). To enter the cranial cavity, it passes through the foramen spinosum to lie between the meningeal and endosteal layers of dura. Its further course in the middle cranial fossa is described on page 750. The anterior (frontal) branch deeply grooves or tunnels the anteroinferior angle of the parietal bone, and its course corresponds roughly to the line of the underlying precentral gyrus of the brain. The posterior (parietal) branch curves backward and supplies the posterior part of the dura mater. Dural Venous Drainage The meningeal veins lie in the endosteal layer of dura. The middle meningeal vein follows the branches of the middle meningeal artery and drains into the pterygoid venous plexus or the sphenoparietal sinus. The veins lie lateral to the arteries. Arachnoid Mater of the Brain The arachnoid mater is a delicate, impermeable membrane covering the brain and lying between the pia mater internally and the dura mater externally (Fig. 11-2). It is separated from the dura by a potential space, the subdural space, and from the pia by the subarachnoid space, which is filled with cerebrospinal fluid. The arachnoid bridges over the sulci on the surface of the brain, and in certain situations the arachnoid and pia are widely separated to form the subarachnoid cisternae. In certain areas the arachnoid projects into the venous sinuses to form arachnoid villi. The arachnoid villi are most numerous along the superior sagittal sinus. Aggregations of arachnoid villi are referred to as arachnoid granulations (Fig. 11-2). Arachnoid villi serve as sites where the cerebrospinal fluid diffuses into the bloodstream. It is important to remember that structures passing to and from the brain to the skull or its foramina must pass through the subarachnoid space. All the cerebral arteries and veins lie in the space, as do the cranial nerves (Fig. 11-2). The arachnoid fuses with the epineurium of the nerves at their point of exit from the skull. In the case of the optic nerve, the P.684
arachnoid forms a sheath for the nerve that extends into the orbital cavity through the optic canal and fuses with the sclera of the eyeball (Fig. 11-25). Thus, the subarachnoid space extends around the optic nerve as far as the eyeball (see page 697).

Figure 11-12 A. The forebrain has been removed, leaving the midbrain, the hypophysis cerebri, and the internal carotid and basilar arteries in position. B. Sagittal section through the sella turcica showing the hypophysis cerebri. C. Coronal section through the body of the sphenoid showing the hypophysis cerebri and the cavernous sinuses. Note the position of the cranial nerves.

The cerebrospinal fluid is produced by the choroid plexuses within the lateral, third, and fourth ventricles of the brain. It escapes from the ventricular system of the brain through the three foramina in the roof of the fourth ventricle and so enters the subarachnoid space. It now circulates both upward over the surfaces of the cerebral hemispheres and downward around the spinal cord. The spinal subarachnoid space extends down as far as the second sacral vertebra (see Fig. 12-7). Eventually, the fluid enters the P.685
bloodstream by passing into the arachnoid villi and diffusing through their walls.

Figure 11-13 Sagittal section of the head and neck.

In addition to removing waste products associated with neuronal activity, the cerebrospinal fluid provides a fluid medium in which the brain floats. This mechanism effectively protects the brain from trauma. Pia Mater of the Brain The pia mater is a vascular membrane that closely invests the brain, covering the gyri and descending into the deepest sulci (Fig. 11-2). It extends over the cranial nerves and fuses with their epineurium. The cerebral arteries entering the substance of the brain carry a sheath of pia with them. P.686
Clinical Notes Intracranial Hemorrhage Intracranial hemorrhage may result from trauma or cerebral vascular lesions. Four varieties are considered here: extradural, subdural, subarachnoid, and cerebral. Extradural hemorrhage results from injuries to the meningeal arteries or veins. The most common artery to be damaged is the anterior division of the middle meningeal artery. A comparatively minor blow to the side of the head, resulting in fracture of the skull in the region of the anteroinferior portion of the parietal bone, may sever the artery. The arterial or venous injury is especially liable to occur if the artery and vein enter a bony canal in this region. Bleeding occurs and strips up the meningeal layer of dura from the internal surface of the skull. The intracranial pressure rises, and the enlarging blood clot exerts local pressure on the underlying motor area in the precentral gyrus. Blood may also pass outward through the fracture line to form a soft swelling under the temporalis muscle. To stop the hemorrhage, the torn artery or vein must be ligated or plugged. The burr hole through the skull wall should be placed about 1 to 1.5 in. (2.5 to 4 cm) above the midpoint of the zygomatic arch. Subdural hemorrhage results from tearing of the superior cerebral veins at their point of entrance into the superior sagittal sinus. The cause is usually a blow on the front or the back of the head, causing excessive anteroposterior displacement of the brain within the skull. This condition, which is much more common than middle meningeal hemorrhage, can be produced by a sudden minor blow. Once the vein is torn, blood under low pressure begins to accumulate in the potential space between the dura and the arachnoid. In about half the cases the condition is bilateral. Acute and chronic forms of the clinical condition occur, depending on the speed of accumulation of fluid in the subdural space. For example, if the patient starts to vomit, the venous pressure will rise as a result of a rise in the intrathoracic pressure. Under these circumstances, the subdural blood clot will increase rapidly in size and produce acute symptoms. In the chronic form, over a course of several months, the small blood clot will attract fluid by osmosis so that a hemorrhagic cyst is formed, which gradually expands and produces pressure symptoms. In both forms the blood clot must be removed through burr holes in the skull. Subarachnoid hemorrhage results from leakage or rupture of a congenital aneurysm on the circle of Willis or, less commonly, from an angioma. The symptoms, which are sudden in onset, include severe headache, stiffness of the neck, and loss of consciousness. The diagnosis is established by withdrawing heavily blood-stained cerebrospinal fluid through a lumbar puncture (spinal tap). Cerebral hemorrhage is generally caused by rupture of the thin-walled lenticulostriate artery, a branch of the middle cerebral artery. The hemorrhage involves the vital corticobulbar and corticospinal fibers in the internal capsule and produces hemiplegia on the opposite side of the body. The patient immediately loses consciousness, and the paralysis is evident when consciousness is regained. Intracranial Hemorrhage in the Infant Intracranial hemorrhage in the infant may occur during birth and may result from excessive molding of the head. Bleeding may occur from the cerebral veins or the venous sinuses. Excessive anteroposterior compression of the head often tears the anterior attachment of the falx cerebri from the tentorium cerebelli. Bleeding then takes place from the great cerebral veins, the straight sinus, or the inferior sagittal sinus. The Venous Blood Sinuses The venous sinuses of the cranial cavity are blood-filled spaces situated between the layers of the dura mater (Fig. 11-2); they are lined by endothelium. Their walls are thick and composed of fibrous tissue; they have no muscular tissue. The sinuses have no valves. They receive tributaries from the brain, the diploë of the skull, the orbit, and the internal ear. The superior sagittal sinus lies in the upper fixed border of the falx cerebri (Fig. 11-9). It runs backward and becomes continuous with the right transverse sinus. The sinus communicates on each side with the venous lacunae. Numerous arachnoid villi and granulations project into the lacunae (Fig. 11-2). The superior sagittal sinus receives the superior cerebral veins. The inferior sagittal sinus lies in the free lower margin of the falx cerebri. It runs backward and joins the great cerebral vein to form the straight sinus (Fig. 11-9). It receives cerebral veins from the medial surface of the cerebral hemisphere. The straight sinus lies at the junction of the falx cerebri with the tentorium cerebelli (Fig. 11-9). Formed by the union of the inferior sagittal sinus with the great cerebral vein, it drains into the left transverse sinus. The right transverse sinus begins as a continuation of the superior sagittal sinus; the left transverse sinus is usually a continuation of the straight sinus (Figs. 11-9 and 11-10). Each sinus lies in the lateral attached margin of the tentorium cerebelli, and they end on each side by becoming the sigmoid sinus. The sigmoid sinuses are a direct continuation of the transverse sinuses. Each sinus turns downward behind the mastoid antrum of the temporal bone and then leaves the skull through the jugular foramen to become the internal jugular vein (Fig. 11-30). The occipital sinus lies in the attached margin of the falx cerebelli. It communicates with the vertebral veins through the foramen magnum and the transverse sinuses. Each cavernous sinus lies on the lateral side of the body of the sphenoid bone (Fig. 11-9). Anteriorly, the sinus receives the inferior ophthalmic vein and the central vein of the retina. The sinus drains posteriorly into the transverse sinus through the superior petrosal sinus. Intercavernous sinuses connect the two cavernous sinuses through the sella turcica. P.687
Important Structures Associated With the Cavernous Sinuses

  • The internal carotid artery and the sixth cranial nerve, which travel through it (Fig. 11-12)
  • In the lateral wall, the third and fourth cranial nerves, and the ophthalmic and maxillary divisions of the fifth cranial nerve (Fig. 11-12).
  • The pituitary gland, which lies medially in the sella turcica (Fig. 11-12)
  • The veins of the face, which are connected with the cavernous sinus via the facial vein and inferior ophthalmic vein, and are an important route for the spread of infection from the face (Fig. 11-9)
  • The superior and inferior petrosal sinuses, which run along the upper and lower borders of the petrous part of the temporal bone (Fig. 11-9)

Pituitary Gland (Hypophysis Cerebri) The pituitary gland is a small, oval structure attached to the undersurface of the brain by the infundibulum (Fig. 11-12). The gland is well protected by virtue of its location in the sella turcica of the sphenoid bone. The pituitary gland is vital to life and is fully described on page 815. Parts of the Brain For a detailed description of the gross structure of the brain, a textbook of neuroanatomy should be consulted. In the following account, only the main parts of the brain are described.

The brain is that part of the central nervous system that lies inside the cranial cavity. It is continuous with the spinal cord through the foramen magnum. Cerebrum The cerebrum is the largest part of the brain and consists of two cerebral hemispheres connected by a mass of white matter called the corpus callosum (Fig. 11-13). Each hemisphere extends from the frontal to the occipital bones; above the anterior and middle cranial fossae; and, posteriorly, above the tentorium cerebelli. The hemispheres are separated by a deep cleft, the longitudinal fissure, into which projects the falx cerebri (Fig. 11-13). The surface layer of each hemisphere is called the cortex and is composed of gray matter (Fig. 11-2). The cerebral cortex is thrown into folds, or gyri, separated by fissures, or sulci. By this means the surface area of the cortex is greatly increased. Several of the large sulci conveniently subdivide the surface of each hemisphere into lobes. The lobes are named for the bones of the cranium under which they lie (Fig. 11-14). The frontal lobe is situated in front of the central sulcus (Fig. 11-14) and above the lateral sulcus. The parietal lobe is situated behind the central sulcus and above the lateral sulcus. The occipital lobe lies below the parieto-occipital sulcus. Below the lateral sulcus is situated the temporal lobe. The precentral gyrus lies immediately anterior to the central sulcus and is known as the motor area (Fig. 11-14). The large motor nerve cells in this area control voluntary movements on the opposite side of the body. Most nerve fibers cross over to the opposite side in the medulla oblongata as they descend to the spinal cord. In the motor area, the body is represented in an inverted position, with the nerve cells controlling the movements of the feet located in the upper part and those controlling the movements of the face and hands in the lower part (Fig. 11-14). The postcentral gyrus lies immediately posterior to the central sulcus and is known as the sensory area (Fig. 11-14). The small nerve cells in this area receive and interpret sensations of pain, temperature, touch, and pressure from the opposite side of the body. The superior temporal gyrus lies immediately below the lateral sulcus (Fig. 11-14). The middle of this gyrus is concerned with the reception and interpretation of sound and is known as the auditory area. Broca’s area, or the motor speech area, lies just above the lateral sulcus (Fig. 11-14). It controls the movements employed in speech. It is dominant in the left hemisphere in right-handed persons and in the right hemisphere in left-handed persons. The visual area is situated on the posterior pole and medial aspect of the cerebral hemisphere in the region of the calcarine sulcus (Fig. 11-14). It is the receiving area for visual impressions. The cavity present within each cerebral hemisphere is called the lateral ventricle. The lateral ventricles communicate with the third ventricle through the interventricular foramina (Fig. 11-13). Diencephalon The diencephalon is almost completely hidden from the surface of the brain. It consists of a dorsal thalamus (Fig. 11-13) and a ventral hypothalamus. The thalamus is a large mass of gray matter that lies on either side of the third ventricle. It is the great relay station on the afferent sensory pathway to the cerebral cortex. The hypothalamus forms the lower part of the lateral wall and floor of the third ventricle. The following structures are found in the floor of the third ventricle from before backward: the optic chiasma (Fig. 11-15), the tuber cinereum and the infundibulum, the mammillary bodies, and the posterior perforated substance. P.688

Figure 11-14 A. Right side of the brain showing some important localized areas of cerebral function. Note that the motor speech area is most commonly located in the left rather than the right cerebral hemisphere. B. Lateral surface of the cerebral hemisphere showing areas supplied by the cerebral arteries. In this and the next figure, areas colored blue are supplied by the anterior cerebral artery; those colored red, by the middle cerebral artery; and those colored green, by the posterior cerebral artery. C. Medial surface of the cerebral hemisphere showing the areas supplied by the cerebral arteries.

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Figure 11-15 Arteries and cranial nerves seen on the inferior surface of the brain. To show the course of the middle cerebral artery, the anterior pole of the left temporal lobe has been removed.

Midbrain The midbrain is the narrow part of the brain that passes through the tentorial notch and connects the forebrain to the hindbrain (Fig. 11-13). The midbrain comprises two lateral halves called the cerebral peduncles; each of these is divided into an anterior part, the crus cerebri, and a posterior part, the tegmentum, by a pigmented band of gray matter, the substantia nigra (Fig. 11-12). The narrow cavity of the midbrain is the cerebral aqueduct, which connects the third and fourth ventricles. The tectum is the part of the midbrain posterior to the cerebral aqueduct; it has four small surface swellings, namely, the two superior (Fig. 11-12) and two inferior colliculi. The colliculi are deeply placed between the cerebellum and the cerebral hemispheres. The pineal body is a small glandular structure that lies between the superior colliculi (Fig. 11-13). It is attached by a stalk to the region of the posterior wall of the third ventricle (see also page 816). The pineal commonly calcifies in middle age, and thus it can be visualized on radiographs. Hindbrain The pons is situated on the anterior surface of the cerebellum below the midbrain and above the medulla oblongata (Fig. 11-13). It is composed mainly of nerve fibers, which connect the two halves of the cerebellum. It also contains ascending and descending fibers connecting the forebrain, the midbrain, and the spinal cord. Some of the nerve cells within the pons serve as relay stations, whereas others form cranial nerve nuclei. P.690
The medulla oblongata is conical in shape and connects the pons above to the spinal cord below (Fig. 11-13). A median fissure is present on the anterior surface of the medulla, and on each side of this is a swelling called the pyramid (Fig. 11-15). The pyramids are composed of bundles of nerve fibers that originate in large nerve cells in the precentral gyrus of the cerebral cortex. The pyramids taper below, and here most of the descending fibers cross over to the opposite side, forming the decussation of the pyramids. Posterior to the pyramids are the olives, which are oval elevations produced by the underlying olivary nuclei (Fig. 11-15). Behind the olives are the inferior cerebellar peduncles, which connect the medulla to the cerebellum. On the posterior surface of the inferior part of the medulla oblongata are the gracile and cuneate tubercles, produced by the medially placed underlying nucleus gracilis and the laterally placed underlying nucleus cuneatus. The cerebellum lies within the posterior cranial fossa beneath the tentorium cerebelli (Fig. 11-13). It is situated posterior to the pons and the medulla oblongata. It consists of two hemispheres connected by a median portion, the vermis. The cerebellum is connected to the midbrain by the superior cerebellar peduncles, to the pons by the middle cerebellar peduncles, and to the medulla by the inferior cerebellar peduncles. The surface layer of each cerebellar hemisphere, called the cortex, is composed of gray matter. The cerebellar cortex is thrown into folds, or folia, separated by closely set transverse fissures. Certain masses of gray matter are found in the interior of the cerebellum, embedded in the white matter; the largest of these is known as the dentate nucleus. The cerebellum plays an important role in the control of muscle tone and the coordination of muscle movement on the same side of the body. The cavity of the hindbrain is the fourth ventricle (Fig. 11-13). This is bounded in front by the pons and the medulla oblongata and behind by the superior and inferior medullary vela and the cerebellum. The fourth ventricle is connected above to the third ventricle by the cerebral aqueduct, and below it is continuous with the central canal of the spinal cord. It communicates with the subarachnoid space through three openings in the lower part of the roof: a median and two lateral openings. Ventricles of the Brain The ventricles of the brain consist of the two lateral ventricles, the third ventricle, and the fourth ventricle. The two lateral ventricles communicate with the third ventricle through the interventricular foramina (Fig. 11-13); the third ventricle communicates with the fourth ventricle by the cerebral aqueduct. The fourth ventricle, in turn, is continuous with the narrow central canal of the spinal cord and, through the three foramina in its roof, with the subarachnoid space. The ventricles are filled with cerebrospinal fluid, which is produced by the choroid plexuses of the two lateral ventricles, the third ventricle, and the fourth ventricle. The size and shape of the cerebral ventricles may be visualized clinically using computed tomography (CT) scans and magnetic resonance imaging (MRI) (Figs. 11-127, 11-128, and 11-129). Blood Supply of the Brain Arteries of the Brain The brain is supplied by the two internal carotid and the two vertebral arteries. The four arteries anastomose on the inferior surface of the brain and form the circle of Willis (circulus arteriosus). The internal carotid arteries, the vertebral arteries, and the circle of Willis are fully described on page 750 and 751. Veins of the Brain The veins of the brain have no muscular tissue in their thin walls, and they possess no valves. They emerge from the brain and drain into the cranial venous sinuses (Fig. 11-2). Cerebral and cerebellar veins and veins of the brainstem are present. The great cerebral vein is formed by the union of the two internal cerebral veins and drains into the straight sinus (Fig. 11-9). Clinical Notes Brain Injuries Injuries of the brain are produced by displacement and distortion of the neuronal tissues at the moment of impact. The brain may be likened to a log soaked with water floating submerged in water. The brain is floating in the cerebrospinal fluid in the subarachnoid space and is capable of a certain amount of anteroposterior movement, which is limited by the attachment of the superior cerebral veins to the superior sagittal sinus. Lateral displacement of the brain is limited by the falx cerebri. The tentorium cerebelli and the falx cerebelli also restrict displacement of the brain. It follows from these anatomic facts that blows on the front or back of the head lead to displacement of the brain, which may produce severe cerebral damage, stretching and distortion of the brainstem, and stretching and even tearing of the commissures of the brain. The terms concussion, contusion, and laceration are used clinically to describe the degrees of brain injury. Blows on the side of the head produce less cerebral displacement, and the injuries to the brain consequently tend to be less severe. P.691
The Cranial Nerves in the Cranial Cavity The 12 pairs of cranial nerves are named as follows:

  • I. Olfactory (sensory)
  • II. Optic (sensory)
  • III. Oculomotor (motor)
  • IV. Trochlear (motor)
  • V. Trigeminal (mixed)
  • VI. Abducent (motor)
  • VII. Facial (mixed)
  • VIII. Vestibulocochlear (sensory)
  • IX. Glossopharyngeal (mixed)
  • X. Vagus (mixed)
  • XI. Accessory (motor)
  • XII. Hypoglossal (motor)

The nerves emerge from the brain and are transmitted through foramina and fissures in the base of the skull. All the nerves are distributed in the head and neck except the vagus, which also supplies structures in the thorax and abdomen. The olfactory, optic, and vestibulocochlear nerves are entirely sensory; the oculomotor, trochlear, abducent, accessory, and hypoglossal nerves are entirely motor; and the remaining nerves are mixed. The origins and courses of the cranial nerves are described on page 757. The cranial nerves, their component parts, their function, and the openings through which they exit from the skull are summarized in Table 11-6. The Orbital Region The orbits are a pair of bony cavities that contain the eyeballs; their associated muscles, nerves, vessels, and fat; and most of the lacrimal apparatus. The orbital opening is guarded by two thin, movable folds, the eyelids. Eyelids The eyelids protect the eye from injury and excessive light by their closure (Fig. 11-16). The upper eyelid is larger and more mobile than the lower, and they meet each other at the medial and lateral angles. The palpebral fissure is the elliptical opening between the eyelids and is the entrance into the conjunctival sac. When the eye is closed, the upper eyelid completely covers the cornea of the eye. When the eye is open and looking straight ahead, the upper lid just covers the upper margin of the cornea. The lower lid lies just below the cornea when the eye is open and rises only slightly when the eye is closed. The superficial surface of the eyelids is covered by skin, and the deep surface is covered by a mucous membrane, called the conjunctiva. The eyelashes are short, curved hairs on the free edges of the eyelids (Figs. 11-16 and 11-17). They are arranged in double or triple rows at the mucocutaneous junction. The sebaceous glands (glands of Zeis) open directly into the eyelash follicles. The ciliary glands (glands of Moll) are modified sweat glands that open separately between adjacent lashes. The tarsal glands are long, modified sebaceous glands that pour their oily secretion onto the margin of the lid; their openings lie behind the eyelashes (Fig. 11-16). This oily material prevents the overflow of tears and helps make the closed eyelids airtight. The more rounded medial angle is separated from the eyeball by a small space, the lacus lacrimalis, in the center of which is a small, reddish yellow elevation, the caruncula lacrimalis (Figs. 11-16 and 11-17). A reddish semilunar fold, called the plica semilunaris, lies on the lateral side of the caruncle. Near the medial angle of the eye a small elevation, the papilla lacrimalis, is present. On the summit of the papilla is a small hole, the punctum lacrimale, which leads into the canaliculus lacrimalis (Figs. 11-16 and 11-17). The papilla lacrimalis projects into the lacus, and the punctum and canaliculus carry tears down into the nose (see page 694). The conjunctiva is a thin mucous membrane that lines the eyelids and is reflected at the superior and inferior fornices onto the anterior surface of the eyeball (Fig. 11-16). Its epithelium is continuous with that of the cornea. The upper lateral part of the superior fornix is pierced by the ducts of the lacrimal gland (see below). The conjunctiva thus forms a potential space, the conjunctival sac, which is open at the palpebral fissure. Beneath the eyelid is a groove, the subtarsal sulcus, which runs close to and parallel with the margin of the lid (Fig. 11-16). The sulcus tends to trap small foreign particles introduced into the conjunctival sac and is thus clinically important. The framework of the eyelids is formed by a fibrous sheet, the orbital septum (Fig. 11-16). This is attached to the periosteum at the orbital margins. The orbital septum is thickened at the margins of the lids to form the superior and inferior tarsal plates. The lateral ends of the plates are attached by a band, the lateral palpebral ligament, to a bony tubercle just within the orbital margin. The medial ends of the plates are attached by a band, the medial palpebral ligament, to the crest of the lacrimal bone (Fig. 11-16). The tarsal glands are embedded in the posterior surface of the tarsal plates. The superficial surface of the tarsal plates and the orbital septum are covered by the palpebral fibers of the orbicularis oculi muscle (Table 11-16). The aponeurosis of insertion of the levator palpebrae superioris muscle pierces the orbital septum to reach the anterior surface of the superior tarsal plate and the skin (Fig. 11-16). Movements of the Eyelids The position of the eyelids at rest depends on the tone of the orbicularis oculi and the levator palpebrae superioris muscles and the position of the eyeball. The eyelids are closed by the contraction of the orbicularis oculi and the relaxation of the levator palpebrae superioris muscles. The eye is opened by the levator palpebrae superioris raising the upper lid. On looking upward, the levator palpebrae superioris contracts, and the upper lid moves with the eyeball. On looking downward, both lids move, the upper lid continues to cover the upper part of the cornea, and the lower lid is pulled downward slightly by the conjunctiva, which is attached to the sclera and the lower lid. The origins and insertions of the muscles of the eyelids are summarized in Table 11-2. P.692

Figure 11-16 A. Right eye, with the eyelids separated to show the openings of the tarsal glands, plica semilunaris, caruncula lacrimalis, and puncta lacrimalis. B. Left eye, showing the superior and inferior tarsal plates and the lacrimal gland, sac, and duct. Note that a small window has been cut in the orbital septum to show the underlying lacrimal gland and fat (yellow). C. Sagittal section through the upper eyelid, and the superior fornix of the conjunctiva. Note the presence of smooth muscle in the levator palpebrae superioris.

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Figure 11-17 Left eye of a 29-year-old woman. A. The names of structures seen in the examination of the eye. B. An enlarged view of the medial angle between the eyelids. C. The lower eyelid pulled downward and slightly everted to reveal the punctum lacrimale.

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Table 11-2 Muscles of the Eyeball and Eyelids
Muscle Origin Insertion Nerve Supply Action
Extrinsic Muscles of Eyeball (Striated Skeletal Muscle)
Superior rectus Tendinous ring on posterior wall of orbital cavity Superior surface of eyeball just posterior to corneoscleral junction Oculomotor nerve (third cranial nerve) Raises cornea upward and medially
Inferior rectus Tendinous ring on posterior wall of orbital cavity Inferior surface of eyeball just posterior to corneoscleral junction Oculomotor nerve (third cranial nerve) Depresses cornea downward and medially
Medial rectus Tendinous ring on posterior wall of orbital cavity Medial surface of eyeball just posterior to corneoscleral junction Oculomotor nerve (third cranial nerve) Rotates eyeball so that cornea looks medially
Lateral rectus Tendinous ring on posterior wall of orbital cavity Lateral surface of eyeball just posterior to corneoscleral junction Abducent nerve (sixth cranial nerve) Rotates eyeball so that cornea looks laterally
Superior oblique Posterior wall of orbital cavity Passes through pulley and is attached to superior surface of eyeball beneath superior rectus Trochlear nerve (fourth cranial nerve) Rotates eyeball so that cornea looks downward and laterally
Inferior oblique Floor of orbital cavity Lateral surface of eyeball deep to lateral rectus Oculomotor nerve (third cranial nerve) Rotates eyeball so that cornea looks upward and laterally
Intrinsic Muscles of Eyeball (Smooth Muscle)
Sphincter pupillae of iris     Parasympathetic via oculomotor nerve Constricts pupil
Dilator pupillae of iris     Sympathetic Dilates pupil
Ciliary muscle     Parasympathetic via oculomotor nerve Controls shape of lens; in accommodation, makes lens more globular
Muscles of Eyelids
Orbicularis oculi (Table 11-4)
Levator palpebrae superioris Back of orbital cavity Anterior surface and upper margin of superior tarsal plate Striated muscle oculomotor nerve, smooth muscle sympathetic Raises upper lid

Lacrimal Apparatus Lacrimal Gland The lacrimal gland consists of a large orbital part and a small palpebral part, which are continuous with each other around the lateral edge of the aponeurosis of the levator palpebrae superioris. It is situated above the eyeball in the anterior and upper part of the orbit posterior to the orbital septum (Fig. 11-16). The gland opens into the lateral part of the superior fornix of the conjunctiva by 12 ducts. The parasympathetic secretomotor nerve supply is derived from the lacrimal nucleus of the facial nerve. The preganglionic fibers reach the pterygopalatine ganglion (sphenopalatine ganglion) via the nervus intermedius and its great petrosal branch and via the nerve of the pterygoid canal. The postganglionic fibers leave the ganglion and join the maxillary nerve. They then pass into its zygomatic branch and the zygomaticotemporal nerve. They reach the lacrimal gland within the lacrimal nerve. The sympathetic postganglionic nerve supply is from the internal carotid plexus and travels in the deep petrosal nerve, the nerve of the pterygoid canal, the maxillary nerve, the zygomatic nerve, the zygomaticotemporal nerve, and finally the lacrimal nerve. Lacrimal Ducts The tears circulate across the cornea and accumulate in the lacus lacrimalis. From here, the tears enter the canaliculi lacrimales through the puncta lacrimalis. The canaliculi lacrimales pass medially and open into the lacrimal sac (Fig. 11-16), which lies in the lacrimal groove behind the medial palpebral ligament and is the upper blind end of the nasolacrimal duct. The nasolacrimal duct is about 0.5 in. (1.3 cm) long and emerges from the lower end of the lacrimal sac (Fig. 11-16). The duct descends downward, backward, and laterally in a bony canal and opens into the inferior meatus of the nose. The opening is guarded by a fold of mucous membrane P.695
known as the lacrimal fold. This prevents air from being forced up the duct into the lacrimal sac on blowing the nose. The Orbit Description The orbit is a pyramidal cavity with its base in front and its apex behind (Fig. 11-18). The orbital margin is formed above by the frontal bone, the lateral margin is formed by the processes of the frontal and zygomatic bones, the inferior margin is formed by the zygomatic bone and the maxilla, and the medial margin is formed by the processes of the maxilla and the frontal bone. The orbital walls are shown in Figure 11-18.

  • Roof: Formed by the orbital plate of the frontal bone, which separates the orbital cavity from the anterior cranial fossa and the frontal lobe of the cerebral hemisphere P.696
    Figure 11-18 A. Right eyeball exposed from in front. B. Muscles and nerves of the left orbit as seen from in front. C. Bones forming the walls of the right orbit. D. The optic canal and the superior and inferior orbital fissures on the left side.
  • Lateral wall: Formed by the zygomatic bone and the greater wing of the sphenoid (Fig. 11-18)
  • Floor: Formed by the orbital plate of the maxilla, which separates the orbital cavity from the maxillary sinus
  • Medial wall: Formed from before backward by the frontal process of the maxilla, the lacrimal bone, the orbital plate of the ethmoid (which separates the orbital cavity from the ethmoid sinuses), and the body of the sphenoid

Openings Into the Orbital Cavity The openings into the orbital cavity are shown in Figure 11-18.

  • Orbital opening: Lies anteriorly (Fig. 11-18). About one-sixth of the eye is exposed; the remainder is protected by the walls of the orbit.
  • Supraorbital notch (Foramen): The supraorbital notch is situated on the superior orbital margin (Fig. 11-18). It transmits the supraorbital nerve and blood vessels.
  • Infraorbital groove and canal: Situated on the floor of the orbit in the orbital plate of the maxilla (Fig. 11-19); they transmit the infraorbital nerve (a continuation of the maxillary nerve) and blood vessels.
  • Nasolacrimal canal: Located anteriorly on the medial wall; it communicates with the inferior meatus of the nose (Fig. 11-16). It transmits the nasolacrimal duct.
  • Inferior orbital fissure: Located posteriorly between the maxilla and the greater wing of the sphenoid (Fig. 11-18); it communicates with the pterygopalatine fossa. It transmits the maxillary nerve and its zygomatic branch, the inferior ophthalmic vein, and sympathetic nerves.
  • Superior orbital fissure: Located posteriorly between the greater and lesser wings of the sphenoid (Fig. 11-18); it communicates with the middle cranial fossa. It transmits the lacrimal nerve, the frontal nerve, the trochlear nerve, the oculomotor nerve (upper and lower divisions), the abducent nerve, the nasociliary nerve, and the superior ophthalmic vein.
  • Optic canal: Located posteriorly in the lesser wing of the sphenoid (Fig. 11-18); it communicates with the middle cranial fossa. It transmits the optic nerve and the ophthalmic artery.
Figure 11-19 Muscles and nerves of the right orbit viewed from the lateral side. The maxillary nerve and the pterygopalatine ganglion are also shown.

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Orbital Fascia The orbital fascia is the periosteum of the bones that form the walls of the orbit. It is loosely attached to the bones and is continuous through the foramina and fissures with the periosteum covering the outer surfaces of the bones. The muscle of Müller, or orbitalis muscle, is a thin layer of smooth muscle that bridges the inferior orbital fissure. It is supplied by sympathetic nerves, and its function is unknown. Nerves of the Orbit Optic Nerve The optic nerve enters the orbit from the middle cranial fossa by passing through the optic canal (Fig. 11-20). It is accompanied by the ophthalmic artery, which lies on its lower lateral side. The nerve is surrounded by sheaths of pia mater, arachnoid mater, and dura mater (Fig. 11-25). It runs forward and laterally within the cone of the recti muscles and pierces the sclera at a point medial to the posterior pole of the eyeball. Here, the meninges fuse with the sclera so that the subarachnoid space with its contained cerebrospinal fluid extends forward from the middle cranial fossa, around the optic nerve, and through the optic canal, as far as the eyeball. A rise in pressure of the cerebrospinal fluid within the cranial cavity therefore is transmitted to the back of the eyeball. Lacrimal Nerve The lacrimal nerve arises from the ophthalmic division of the trigeminal nerve. It enters the orbit through the upper part of the superior orbital fissure (Fig. 11-18) and passes forward along the upper border of the lateral rectus muscle (Fig. 11-20). It is joined by a branch of the zygomaticotemporal nerve, which later leaves it to enter the lacrimal gland P.698
(parasympathetic secretomotor fibers). The lacrimal nerve ends by supplying the skin of the lateral part of the upper lid.

Figure 11-20 Right and left orbital cavities viewed from above. The roof of the orbit, formed by the orbital plate of the frontal bone, has been removed from both sides. On the left side, the levator palpebrae superioris and the superior rectus muscles have also been removed to expose the underlying structures.

Frontal Nerve The frontal nerve arises from the ophthalmic division of the trigeminal nerve. It enters the orbit through the upper part of the superior orbital fissure (Fig. 11-18) and passes forward on the upper surface of the levator palpebrae superioris beneath the roof of the orbit (Fig. 11-20). It divides into the supratrochlear and supraorbital nerves that wind around the upper margin of the orbital cavity to supply the skin of the forehead; the supraorbital nerve also supplies the mucous membrane of the frontal air sinus. Trochlear Nerve The trochlear nerve enters the orbit through the upper part of the superior orbital fissure (Fig. 11-18). It runs forward and supplies the superior oblique muscle (Fig. 11-20). Oculomotor Nerve The superior ramus of the oculomotor nerve enters the orbit through the lower part of the superior orbital fissure (Fig. 11-18). It supplies the superior rectus muscle, then pierces it, and supplies the levator palpebrae superioris muscle (Fig. 11-18). The inferior ramus of the oculomotor nerve enters the orbit in a similar manner and supplies the inferior rectus, the medial rectus, and the inferior oblique muscles. The nerve to the inferior oblique gives off a branch (Fig. 11-19) that passes to the ciliary ganglion and carries parasympathetic fibers to the sphincter pupillae and the ciliary muscle (see below). Nasociliary Nerve The nasociliary nerve arises from the ophthalmic division of the trigeminal nerve. It enters the orbit through the lower part of the superior orbital fissure (Fig. 11-18). It crosses above the optic nerve, runs forward along the upper margin of the medial rectus muscle, and ends by dividing into the anterior ethmoidal and infratrochlear nerves (Fig. 11-20). Branches of the Nasociliary Nerve

  • The communicating branch to the ciliary ganglion is a sensory nerve. The sensory fibers from the eyeball pass to the ciliary ganglion via the short ciliary nerves, pass through the ganglion without interruption, and then join the nasociliary nerve by means of the communicating branch.
  • The long ciliary nerves, two or three in number, arise from the nasociliary nerve as it crosses the optic nerve (Fig. 11-20). They contain sympathetic fibers for the dilator pupillae muscle. The nerves pass forward with the short ciliary nerves and pierce the sclera of the eyeball. They continue forward between the sclera and the choroid to reach the iris.
  • The posterior ethmoidal nerve supplies the ethmoidal and sphenoidal air sinuses (Fig. 11-20).
  • The infratrochlear nerve passes forward below the pulley of the superior oblique muscle and supplies the skin of the medial part of the upper eyelid and the adjacent part of the nose (Fig. 11-16).
  • The anterior ethmoidal nerve passes through the anterior ethmoidal foramen and enters the anterior cranial fossa on the upper surface of the cribriform plate of the ethmoid (Fig. 11-20). It enters the nasal cavity through a slitlike opening alongside the crista galli. After supplying an area of mucous membrane, it appears on the face as the external nasal branch at the lower border of the nasal bone, and supplies the skin of the nose down as far as the tip (see page 729).

Abducent Nerve The abducent nerve enters the orbit through the lower part of the superior orbital fissure (Fig. 11-18). It supplies the lateral rectus muscle. Ciliary Ganglion The ciliary ganglion is a parasympathetic ganglion about the size of a pinhead (Fig. 11-19) and situated in the posterior part of the orbit. It receives its preganglionic parasympathetic fibers from the oculomotor nerve via the nerve to the inferior oblique. The postganglionic fibers leave the ganglion in the short ciliary nerves, which enter the back of the eyeball and supply the sphincter pupillae and the ciliary muscle. A number of sympathetic fibers pass from the internal carotid plexus into the orbit and run through the ganglion without interruption. Blood Vessels and Lymph Vessels of the Orbit Ophthalmic Artery The ophthalmic artery is a branch of the internal carotid artery after that vessel emerges from the cavernous sinus (see page 750). It enters the orbit through the optic canal with the optic nerve (Fig. 11-20). It runs forward and crosses the optic nerve to reach the medial wall of the orbit. It gives off numerous branches, which accompany the nerves in the orbital cavity. Branches of the Ophthalmic Artery

  • The central artery of the retina is a small branch that pierces the meningeal sheaths of the optic nerve to gain entrance to the nerve (Figs. 11-25 and 11-26). It runs in the substance of the optic nerve and enters the eyeball at the center of the optic disc. Here, it divides into branches, which may be studied in a patient through an ophthalmoscope. The branches are end arteries.
  • The muscular branches
  • The ciliary arteries can be divided into anterior and posterior groups. The former group enters the eyeball near the corneoscleral junction; the latter group enters near the optic nerve.
  • The lacrimal artery to the lacrimal gland
  • The supratrochlear and supraorbital arteries are distributed to the skin of the forehead (see page 729).

Ophthalmic Veins The superior ophthalmic vein communicates in front with the facial vein (Fig. 11-9). The inferior ophthalmic vein communicates through the inferior orbital fissure with the pterygoid venous plexus. Both veins pass backward through the superior orbital fissure and drain into the cavernous sinus. P.699
Lymph Vessels No lymph vessels or nodes are present in the orbital cavity. The Eye Movements of the Eyeball Terms Used in Describing Eye Movements The center of the cornea or the center of the pupil is used as the anatomic “anterior pole” of the eye. All movements of the eye are then related to the direction of the movement of the anterior pole as it rotates on any one of the three axes (horizontal, vertical, and sagittal). The terminology then becomes as follows: Elevation is the rotation of the eye upward, depression is the rotation of the eye downward, abduction is the rotation of the eye laterally, and adduction is the rotation of the eye medially. Rotatory movements of the eyeball use the upper rim of the cornea (or pupil) as the marker. The eye rotates either medially or laterally.

Figure 11-21 The actions of the four recti muscles in producing movements of the eyeball.

Extrinsic Muscles Producing Movement of the Eye There are six voluntary muscles that run from the posterior wall of the orbital cavity to the eyeball (Fig. 11-18). These are the superior rectus, the inferior rectus, the medial rectus, the lateral rectus, and the superior and inferior oblique muscles. Because the superior and the inferior recti are inserted on the medial side of the vertical axis of the eyeball, they not only raise and depress the cornea, respectively, but also rotate it medially (Fig. 11-21). For the superior rectus muscle to raise the cornea directly upward, the inferior oblique muscle must assist; for the inferior rectus to depress the cornea directly downward, the superior oblique muscle must assist (Figs. 11-21 and 11-22). Note that the tendon of P.700
the superior oblique muscle passes through a fibrocartilaginous pulley (trochlea) attached to the frontal bone. The tendon now turns backward and laterally and is inserted into the sclera beneath the superior rectus muscle.

Figure 11-22 The actions of the superior and inferior oblique muscles in producing movements of the eyeball.

The origins, insertions, nerve supply, and actions of the muscles of the eyeball are summarized in Table 11-2. Study carefully Figure 11-24. Clinical Testing for the Actions of the Superior and Inferior Recti and the Superior and Inferior Oblique Muscles Because the actions of the superior and inferior recti and the superior and inferior oblique muscles are complicated when a patient is asked to look vertically upward or vertically downward, the physician tests the eye movements where the single action of each muscle predominates. The origins of the superior and inferior recti are situated about 23° medial to their insertions, and, therefore, when the patient is asked to turn the cornea laterally, these muscles are placed in the optimum position to raise (superior rectus) or lower (inferior rectus) the cornea. Using the same rationale, the superior and inferior oblique muscles can be tested. The pulley of the superior oblique and the origin of the inferior oblique muscles lie medial and anterior to their insertions. The physician tests the action of these muscles by asking the patient first to look medially, thus placing these muscles in the optimum position to lower (superior oblique) or raise (inferior oblique) the cornea. In other words, when you ask a patient to look medially and downward at the tip of his or her nose, you are testing the superior oblique at its best position. Conversely, by asking the patient to look medially and upward, you are testing the inferior oblique at its best position. Because the lateral and medial recti are simply placed relative to the eyeball, asking the patient to turn his or her cornea directly laterally tests the lateral rectus and turning the cornea directly medially tests the medial rectus. P.701

Figure 11-23 Actions of the four recti and two oblique muscles of the right orbit, assuming that each muscle is acting alone. The position of the pupil in relation to the vertical and horizontal planes should be noted in each case. The actions of the superior and inferior recti and the oblique muscles in the living intact eye are tested clinically, as described on page 700.

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Figure 11-24 The cardinal positions of the right and left eyes and the actions of the recti and oblique muscles principally responsible for the movements of the eyes. A. Right eye, superior rectus muscle; left eye, inferior oblique muscle. B. Both eyes, superior recti and inferior oblique muscles. C. Right eye, inferior oblique muscle; left eye, superior rectus muscle. D. Right eye, lateral rectus muscle; left eye, medial rectus muscle. E. Primary position, with the eyes fixed on a distant fixation point. F. Right eye, medial rectus muscle; left eye, lateral rectus muscle. G. Right eye, inferior rectus muscle; left eye, superior oblique muscle. H. Both eyes, inferior recti and superior oblique muscles. I. Right eye, superior oblique muscle; left eye, inferior rectus muscle.

The cardinal positions of the eyes and the actions of the recti and oblique muscles are shown in Figure 11-24. Intrinsic Muscles The involuntary intrinsic muscles are the ciliary muscle and the constrictor, and the dilator pupillae of the iris take no part in the movement of the eyeball and are discussed later. Fascial Sheath of the Eyeball The fascial sheath surrounds the eyeball from the optic nerve to the corneoscleral junction (Fig. 11-25). It separates the eyeball from the orbital fat and provides it with a socket for free movement. It is perforated by the tendons of the orbital muscles and is reflected onto each of them as a tubular sheath. The sheaths for the tendons of the medial and lateral recti are attached to the medial and lateral walls of the orbit by triangular ligaments called the medial and lateral check ligaments. The lower part of the fascial sheath, which passes beneath the eyeball and connects the check ligaments, is thickened and serves to suspend the eyeball; it is called the suspensory ligament of the eye (Fig. 11-25). By this means the eye is suspended from the medial and lateral walls of the orbit, as if in a hammock. Structure of the Eye The eyeball (Fig. 11-25) is embedded in orbital fat but is separated from it by the fascial sheath of the eyeball. The eyeball P.703
consists of three coats, which, from without inward, are the fibrous coat, the vascular pigmented coat, and the nervous coat.

Figure 11-25 A. Horizontal section through the eyeball and the optic nerve. Note that the central artery and vein of the retina cross the subarachnoid space to reach the optic nerve. B. Check ligaments and suspensory ligament of the eyeball.

Coats of the Eyeball Fibrous Coat The fibrous coat is made up of a posterior opaque part, the sclera, and an anterior transparent part, the cornea (Fig. 11-25). The Sclera The opaque sclera is composed of dense fibrous tissue and is white. Posteriorly, it is pierced by the optic nerve and is fused with the dural sheath of that nerve (Fig. 11-25). The lamina cribrosa is the area of the sclera that is pierced by the nerve fibers of the optic nerve. The sclera is also pierced by the ciliary arteries and nerves and their associated veins, the venae vorticosae. The sclera is directly continuous in front with the cornea at the corneoscleral junction, or limbus. P.704
The Cornea The transparent cornea is largely responsible for the refraction of the light entering the eye (Fig. 11-25). It is in contact posteriorly with the aqueous humor. Blood Supply The cornea is avascular and devoid of lymphatic drainage. It is nourished by diffusion from the aqueous humor and from the capillaries at its edge. Nerve Supply Long ciliary nerves from the ophthalmic division of the trigeminal nerve Function of the Cornea The cornea is the most important refractive medium of the eye. This refractive power occurs on the anterior surface of the cornea, where the refractive index of the cornea (1.38) differs greatly from that of the air. The importance of the tear film in maintaining the normal environment for the corneal epithelial cells should be stressed. Vascular Pigmented Coat The vascular pigmented coat consists, from behind forward, of the choroid, the ciliary body, and the iris. The Choroid The choroid is composed of an outer pigmented layer and an inner, highly vascular layer. The Ciliary Body The ciliary body is continuous posteriorly with the choroid, and anteriorly it lies behind the peripheral margin of the iris (Fig. 11-25). It is composed of the ciliary ring, the ciliary processes, and the ciliary muscle. The ciliary ring is the posterior part of the body, and its surface has shallow grooves, the ciliary striae. The ciliary processes are radially arranged folds, or ridges, to the posterior surfaces of which are connected the suspensory ligaments of the lens. The ciliary muscle (Fig. 11-25) is composed of meridianal and circular fibers of smooth muscle. The meridianal fibers run backward from the region of the corneoscleral junction to the ciliary processes. The circular fibers are fewer in number and lie internal to the meridianal fibers.

  • Nerve supply: The ciliary muscle is supplied by the parasympathetic fibers from the oculomotor nerve. After synapsing in the ciliary ganglion, the postganglionic fibers pass forward to the eyeball in the short ciliary nerves.
  • Action: Contraction of the ciliary muscle, especially the meridianal fibers, pulls the ciliary body forward. This relieves the tension in the suspensory ligament, and the elastic lens becomes more convex. This increases the refractive power of the lens.

The Iris and Pupil The iris is a thin, contractile, pigmented diaphragm with a central aperture, the pupil (Fig. 11-25). It is suspended in the aqueous humor between the cornea and the lens. The periphery of the iris is attached to the anterior surface of the ciliary body. It divides the space between the lens and the cornea into an anterior and a posterior chamber. The muscle fibers of the iris are involuntary and consist of circular and radiating fibers. The circular fibers form the sphincter pupillae and are arranged around the margin of the pupil. The radial fibers form the dilator pupillae and consist of a thin sheet of radial fibers that lie close to the posterior surface.

  • Nerve supply: The sphincter pupillae is supplied by parasympathetic fibers from the oculomotor nerve. After synapsing in the ciliary ganglion, the postganglionic fibers pass forward to the eyeball in the short ciliary nerves. The dilator pupillae is supplied by sympathetic fibers, which pass forward to the eyeball in the long ciliary nerves.
  • Action: The sphincter pupillae constricts the pupil in the presence of bright light and during accommodation. The dilator pupillae dilates the pupil in the presence of light of low intensity or in the presence of excessive sympathetic activity such as occurs in fright.

Nervous Coat: The Retina The retina consists of an outer pigmented layer and an inner nervous layer. Its outer surface is in contact with the choroid, and its inner surface is in contact with the vitreous body (Fig. 11-25). The posterior three fourths of the retina is the receptor organ. Its anterior edge forms a wavy ring, the ora serrata, and the nervous tissues end here. The anterior part of the retina is nonreceptive and consists merely of pigment cells, with a deeper layer of columnar epithelium. This anterior part of the retina covers the ciliary processes and the back of the iris. At the center of the posterior part of the retina is an oval, yellowish area, the macula lutea, which is the area of the retina for the most distinct vision. It has a central depression, the fovea centralis (Figs. 11-25 and 11-26). The optic nerve leaves the retina about 3 mm to the medial side of the macula lutea by the optic disc. The optic disc is slightly depressed at its center, where it is pierced by the central artery of the retina. At the optic disc is a complete absence of rods and cones so that it is insensitive to light and is referred to as the “blind spot.” On ophthalmoscopic examination, the optic disc is seen to be pale pink in color, much paler than the surrounding retina. Contents of the Eyeball The contents of the eyeball consist of the refractive media, the aqueous humor, the vitreous body, and the lens. Aqueous Humor The aqueous humor is a clear fluid that fills the anterior and posterior chambers of the eyeball (Fig. 11-25). It is believed to be a secretion from the ciliary processes, from which it enters the posterior chamber. It then flows into the anterior chamber through the pupil and is drained away through the spaces at the iridocorneal angle into the canal of Schlemm. Obstruction to the draining of the aqueous humor results in a rise in intraocular pressure called glaucoma. This can produce degenerative changes in the retina, with consequent blindness. The function of the aqueous humor is to support the wall of the eyeball by exerting internal pressure and thus maintaining its optical shape. It also nourishes the cornea and the lens and removes the products of metabolism; these functions are important because the cornea and the lens do not possess a blood supply. P.705

Figure 11-26 The left ocular fundus as seen with an ophthalmoscope.

Vitreous Body The vitreous body fills the eyeball behind the lens (Fig. 11-25) and is a transparent gel. The hyaloid canal is a narrow channel that runs through the vitreous body from the optic disc to the posterior surface of the lens; in the fetus, it is filled by the hyaloid artery, which disappears before birth. The function of the vitreous body is to contribute slightly to the magnifying power of the eye. It supports the posterior surface of the lens and assists in holding the neural part of the retina against the pigmented part of the retina. The Lens The lens (Fig. 11-25) is a transparent, biconvex structure enclosed in a transparent capsule. It is situated behind the iris and in front of the vitreous body and is encircled by the ciliary processes. The lens consists of an elastic capsule, which envelops the structure; a cuboidal epithelium, which is confined to the anterior surface of the lens; and lens fibers, which are formed from the cuboidal epithelium at the equator of the lens. The lens fibers make up the bulk of the lens. The elastic lens capsule is under tension, causing the lens constantly to endeavor to assume a globular rather than a disc shape. The equatorial region, or circumference, of the lens is attached to the ciliary processes of the ciliary body by the suspensory ligament. The pull of the radiating fibers of the suspensory ligament tends to keep the elastic lens flattened so that the eye can be focused on distant objects. Accommodation of the Eye To accommodate the eye for close objects, the ciliary muscle contracts and pulls the ciliary body forward and inward so that the radiating fibers of the suspensory ligament are relaxed. This allows the elastic lens to assume a more globular shape. With advancing age, the lens becomes denser and less elastic, and, as a result, the ability to accommodate is lessened (presbyopia). This disability can be overcome by the use of an additional lens in the form of glasses to assist the eye in focusing on nearby objects. Constriction of the Pupil During Accommodation of the Eye To ensure that the light rays pass through the central part of the lens so spherical aberration is diminished during accommodation for near objects, the sphincter pupillae muscle contracts so the pupil becomes smaller Convergence of the Eyes During Accommodation of the Lens In humans, the retinae of both eyes focus on only one set of objects (single binocular vision). When an object moves from a distance toward an individual, the eyes converge so that a single object, not two, is seen. Convergence of the eyes results from the coordinated contraction of the medial rectus muscles. P.706
Clinical Notes Eye Trauma Although the eyeball is well protected by the surrounding bony orbit, it is protected anteriorly only from large objects, such as tennis balls, which tend to strike the orbital margin but not the globe. The bony orbit provides no protection from small objects, such as golf balls, which can cause severe damage to the eye. Careful examination of the eyeball relative to the orbital margins shows that it is least protected from the lateral side. Blowout fractures of the orbital floor involving the maxillary sinus commonly occur as a result of blunt force to the face. If the force is applied to the eye, the orbital fat explodes inferiorly into the maxillary sinus, fracturing the orbital floor. Not only can blowout fractures cause displacement of the eyeball, with resulting symptoms of double vision (diplopia), but also the fracture can injure the infraorbital nerve, producing loss of sensation of the skin of the cheek and the gum on that side. Entrapment of the inferior rectus muscle in the fracture may limit upward gaze. Strabismus Many cases of strabismus are nonparalytic and are caused by an imbalance in the action of opposing muscles. This type of strabismus is known as concomitant strabismus and is common in infancy. Pupillary Reflexes The pupillary reflexes—that is, the reaction of the pupils to light and accommodation—depend on the integrity of nervous pathways. In the direct light reflex, the normal pupil reflexly contracts when a light is shone into the patient’s eye. The nervous impulses pass from the retina along the optic nerve to the optic chiasma and then along the optic tract. Before reaching the lateral geniculate body, the fibers concerned with this reflex leave the tract and pass to the oculomotor nuclei on both sides via the pretectal nuclei. From the parasympathetic part of the nucleus, efferent fibers leave the midbrain in the oculomotor nerve and reach the ciliary ganglion via the nerve to the inferior oblique. Postganglionic fibers pass to the constrictor pupillae muscles via the short ciliary nerves. The consensual light reflex is tested by shining the light in one eye and noting the contraction of the pupil in the opposite eye. This reflex is possible because the afferent pathway just described travels to the parasympathetic nuclei of both oculomotor nerves. The accommodation reflex is the contraction of the pupil that occurs when a person suddenly focuses on a near object after having focused on a distant object. The nervous impulses pass from the retina via the optic nerve, the optic chiasma, the optic tract, the lateral geniculate body, the optic radiation, and the cerebral cortex of the occipital lobe of the brain. The visual cortex is connected to the eye field of the frontal cortex. From here, efferent pathways pass to the parasympathetic nucleus of the oculomotor nerve. From there, the efferent impulses reach the constrictor pupillae via the oculomotor nerve, the ciliary ganglion, and the short ciliary nerves. The Ear The ear consists of the external ear; the middle ear, or tympanic cavity; and the internal ear, or labyrinth, which contains the organs of hearing and balance. External Ear The external ear has an auricle and an external auditory meatus. The auricle has a characteristic shape (Fig. 11-27A) and collects air vibrations. It consists of a thin plate of elastic cartilage covered by skin. It possesses both extrinsic and intrinsic muscles, which are supplied by the facial nerve. The external auditory meatus is a curved tube that leads from the auricle to the tympanic membrane (Figs. 11-27 and 11-28). It conducts sound waves from the auricle to the tympanic membrane. The framework of the outer third of the meatus is elastic cartilage, and the inner two thirds is bone, formed by the tympanic plate. The meatus is lined by skin, and its outer third is provided with hairs and sebaceous and ceruminous glands. The latter are modified sweat glands that secrete a yellowish brown wax. The hairs and the wax provide a sticky barrier that prevents the entrance of foreign bodies. The sensory nerve supply of the lining skin is derived from the auriculotemporal nerve and the auricular branch of the vagus nerve. The lymph drainage is to the superficial parotid, mastoid, and superficial cervical lymph nodes. Clinical Notes Tympanic Membrane Examination Otoscopic examination of the tympanic membrane is facilitated by first straightening the external auditory meatus by gently pulling the auricle upward and backward in the adult, and straight backward or backward and downward in the infant. Normally, the tympanic membrane is pearly gray and concave. Remember that in the adult the external meatus is about 1 in. (2.5 cm) long and is narrowest about 0.2 in. (5 mm) from the tympanic membrane. Middle Ear (Tympanic Cavity) The middle ear is an air-containing cavity in the petrous part of the temporal bone (Fig. 11-28) and is lined with mucous membrane. It contains the auditory ossicles, whose function is to transmit the vibrations of the tympanic membrane (eardrum) to the perilymph of the internal ear. It is a narrow, oblique, slitlike cavity whose long axis lies approximately parallel to the plane of the tympanic membrane. It communicates in front through the auditory tube with the nasopharynx and behind with the mastoid antrum. The middle ear has a roof, floor, anterior wall, posterior wall, lateral wall, and medial wall. P.707

Figure 11-27 A. Different parts of the auricle of the external ear. The arrow indicates the direction that the auricle should be pulled to straighten the external auditory meatus before insertion of the otoscope in the adult. B. External and middle portions of the right ear viewed from in front. C. The right tympanic membrane as seen through the otoscope.

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Figure 11-28 A. Parts of the right ear in relation to the temporal bone viewed from above. B. The auditory ossicles.

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Figure 11-29 A. Lateral wall of the right middle ear viewed from the medial side. Note the position of the ossicles and the mastoid antrum. B. Medial wall of the right middle ear viewed from the lateral side. Note the position of the facial nerve in its bony canal.

The roof is formed by a thin plate of bone, the tegmen tympani, which is part of the petrous temporal bone (Figs. 11-29 and 11-30). It separates the tympanic cavity from the meninges and the temporal lobe of the brain in the middle cranial fossa. The floor is formed by a thin plate of bone, which may be partly replaced by fibrous tissue. It separates the tympanic cavity from the superior bulb of the internal jugular vein (Fig. 11-30). The anterior wall is formed below by a thin plate of bone that separates the tympanic cavity from the internal carotid artery (Fig. 11-30). At the upper part of the anterior wall are the openings into two canals. The lower and larger of these leads into the auditory tube, and the upper and P.710
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smaller is the entrance into the canal for the tensor tympani muscle (Fig. 11-29). The thin, bony septum, which separates the canals, is prolonged backward on the medial wall, where it forms a shelflike projection.

Figure 11-30 A. The middle ear and its relations. Bony (B) and membranous (C) labyrinths.

The posterior wall has in its upper part a large, irregular opening, the aditus to the mastoid antrum (Figs. 11-29 and 11-30). Below this is a small, hollow, conical projection, the pyramid, from whose apex emerges the tendon of the stapedius muscle. The lateral wall is largely formed by the tympanic membrane (Figs. 11-27 and 11-29). The medial wall is formed by the lateral wall of the inner ear. The greater part of the wall shows a rounded projection, called the promontory, which results from the underlying first turn of the cochlea (Figs. 11-27 and 11-29). Above and behind the promontory lies the fenestra vestibuli, which is oval shaped and closed by the base of the stapes. On the medial side of the window is the perilymph of the scala vestibuli of the internal ear. Below the posterior end of the promontory lies the fenestra cochleae, which is round and closed by the secondary tympanic membrane. On the medial side of this window is the perilymph of the blind end of the scala tympani (see page 714). The bony shelf derived from the anterior wall extends backward on the medial wall above the promontory and above the fenestra vestibuli. It supports the tensor tympani muscle. Its posterior end is curved upward and forms a pulley, the processus cochleariformis, around which the tendon of the tensor tympani bends laterally to reach its insertion on the handle of the malleus (Fig. 11-29). A rounded ridge runs horizontally backward above the promontory and the fenestra vestibuli and is known as the prominence of the facial nerve canal. On reaching the posterior wall, it curves downward behind the pyramid. The tympanic membrane (Fig. 11-27) is a thin, fibrous membrane that is pearly gray. The membrane is obliquely placed, facing downward, forward, and laterally. It is concave laterally, and at the depth of the concavity is a small depression, the umbo, produced by the tip of the handle of the malleus. When the membrane is illuminated through an otoscope, the concavity produces a “cone of light,” which radiates anteriorly and inferiorly from the umbo. The tympanic membrane is circular and measures about 1 cm in diameter. The circumference is thickened and is slotted into a groove in the bone. The groove, or tympanic sulcus, is deficient superiorly, which forms a notch. From the sides of the notch, two bands, termed the anterior and posterior malleolar folds, pass to the lateral process of the malleus. The small triangular area on the tympanic membrane that is bounded by the folds is slack and is called the pars flaccida (Fig. 11-27). The remainder of the membrane is tense and is called the pars tensa. The handle of the malleus is bound down to the inner surface of the tympanic membrane by the mucous membrane. The tympanic membrane is extremely sensitive to pain and is innervated on its outer surface by the auriculotemporal nerve and the auricular branch of the vagus. Auditory Ossicles The auditory ossicles are the malleus, incus, and stapes (Figs. 11-28 and 11-29). The malleus is the largest ossicle and possesses a head, a neck, a long process or handle, an anterior process, and a lateral process. The head is rounded and articulates posteriorly with the incus. The neck is the constricted part below the head. The handle passes downward and backward and is firmly attached to the medial surface of the tympanic membrane. It can be seen through the tympanic membrane on otoscopic examination. The anterior process is a spicule of bone that is connected to the anterior wall of the tympanic cavity by a ligament. The lateral process projects laterally and is attached to the anterior and posterior malleolar folds of the tympanic membrane. The incus possesses a large body and two processes (Fig. 11-29). The body is rounded and articulates anteriorly with the head of the malleus. The long process descends behind and parallel to the handle of the malleus. Its lower end bends medially and articulates with the head of the stapes. Its shadow on the tympanic membrane can sometimes be recognized on otoscopic examination. The short process projects backward and is attached to the posterior wall of the tympanic cavity by a ligament. The stapes has a head, a neck, two limbs, and a base (Fig. 11-28). The head is small and articulates with the long process of the incus. The neck is narrow and receives the insertion of the stapedius muscle. The two limbs diverge from the neck and are attached to the oval base. The edge of the base is attached to the margin of the fenestra vestibuli by a ring of fibrous tissue, the anular ligament. Muscles of the Ossicles These are the tensor tympani and the stapedius muscles. The muscles of the ossicles, their nerve supply, and their actions are summarized in Table 11-3.

Table 11-3 Muscles of the Middle Ear
Muscle Origin Insertion Nerve Supply Action
Tensor tympani Wall of auditory tube and wall of its own canal Handle of malleus Mandibular division of trigeminal nerve Dampens down vibrations of tympanic membrane
Stapedius Pyramid (bony projection on posterior wall of middle ear) Neck of stapes Facial nerve Dampens down vibrations of stapes

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Movements of the Auditory Ossicles The malleus and incus rotate on an anteroposterior axis that runs through the ligament connecting the anterior process of the malleus to the anterior wall of the tympanic cavity, the anterior process of the malleus and the short process of the incus, and the ligament connecting the short process of the incus to the posterior wall of the tympanic cavity. When the tympanic membrane moves medially (Fig. 11-31), the handle of the malleus also moves medially. The head of the malleus and the body of the incus move laterally. The long process of the incus moves medially with the stapes. The base of the stapes is pushed medially in the fenestra vestibuli, and the motion is communicated to the perilymph in the scala vestibuli. Liquid being incompressible, the perilymph causes an outward bulging of the secondary tympanic membrane in the fenestra cochleae at the lower end of the scala tympani (Fig. 11-31). The above movements are reversed if the tympanic membrane moves laterally. Excessive lateral movements of the head of the malleus cause a temporary separation of the articular surfaces between the malleus and incus so that the base of the stapes is not pulled laterally out of the fenestra vestibuli. During passage of the vibrations from the tympanic membrane to the perilymph via the small ossicles, the leverage increases at a rate of 1.3 to 1. Moreover, the area of the tympanic membrane is about 17 times greater than that of the base of the stapes, causing the effective pressure on the perilymph to increase by a total of 22 to 1. Auditory Tube The auditory tube connects the anterior wall of the tympanic cavity to the nasal pharynx (Fig. 11-27). Its posterior third is bony, and its anterior two thirds is cartilaginous. As the tube descends it passes over the upper border of the superior constrictor muscle (Fig. 11-80). It serves to equalize air pressures in the tympanic cavity and the nasal pharynx. Mastoid Antrum The mastoid antrum lies behind the middle ear in the petrous part of the temporal bone (Fig. 11-28). It communicates with the middle ear by the aditus (Fig. 11-29). Relations of the Mastoid Antrum These are important in understanding the spread of infection. Anterior wall is related to the middle ear and contains the aditus to the mastoid antrum (Fig. 11-30). Posterior wall separates the antrum from the sigmoid venous sinus and the cerebellum (Fig. 11-30). Lateral wall is (1.5 cm) thick and forms the floor of the suprameatal triangle (see page 838). Medial wall is related to the posterior semicircular canal (Fig. 11-30). Superior wall is the thin plate of bone, the tegmen tympani, which is related to the meninges of the middle cranial fossa and the temporal lobe of the brain (Fig. 11-30). Inferior wall is perforated with holes, through which the antrum communicates with the mastoid air cells (Fig. 11-30). Mastoid Air Cells The mastoid process begins to develop during the second year of life. The mastoid air cells are a series of communicating cavities within the process that are continuous above with the antrum and the middle ear (Fig. 11-30). They are lined with mucous membrane. Facial Nerve The entire course of the facial nerve is described on page 763. On reaching the bottom of the internal acoustic meatus (see page 764), the facial nerve enters the facial canal (Fig. 11-28). The nerve runs laterally above the vestibule of the internal ear until it reaches the medial wall of the middle ear. Here, the nerve expands to form the sensory geniculate ganglion (Figs. 11-29 and 11-30). The nerve then bends sharply backward above the promontory. On arriving at the posterior wall of the middle ear, it curves downward on the medial side of the aditus of the mastoid antrum (Fig. 11-30). It descends in the posterior wall of the middle ear, behind the pyramid, and finally emerges through the stylomastoid foramen into the neck. Important Branches of the Intrapetrous Part of the Facial Nerve

  • The greater petrosal nerve arises from the facial nerve at the geniculate ganglion (Fig. 11-30). It contains preganglionic parasympathetic fibers that pass to the pterygopalatine ganglion and are there relayed through the zygomatic and lacrimal nerves to the lacrimal gland; other postganglionic fibers pass through the nasal and palatine nerves to the glands of the mucous membrane of the nose and palate. It also contains many taste fibers from the mucous membrane of the palate.

The nerve emerges on the superior surface of the petrous part of the temporal bone and is eventually joined by the deep petrosal nerve from the sympathetic plexus on the internal carotid artery and forms the nerve of the pterygoid canal. This passes forward and enters the pterygopalatine fossa, where it ends in the pterygopalatine ganglion.

  • The nerve to the stapedius arises from the facial nerve as it descends in the facial canal behind the pyramid (Fig. 11-30). It supplies the muscle within the pyramid.
  • The chorda tympani arises from the facial nerve just above the stylomastoid foramen (Fig. 11-29). It enters the middle ear close to the posterior border of the tympanic membrane. It then runs forward over the tympanic membrane and crosses the root of the handle of the malleus (Fig. 11-29). It lies in the interval between the mucous membrane and the fibrous layers of the tympanic membrane. The nerve leaves the middle ear through the petrotympanic fissure and enters the infratemporal fossa, where it joins the lingual nerve (see page 765). The chorda tympani contains: Taste fibers from the mucous membrane covering the anterior two thirds of the tongue (not the vallate papillae) and the floor of the mouth. The taste fibers are the peripheral processes of the cells in the geniculate ganglion. P.713
    Figure 11-31 A. Vibrations of music passing into the external auditory meatus cause the tympanic membrane to move medially; the head of the malleus and incus move laterally, and the long process of the incus, with the stapes, moves laterally. B. The medial movement of the base of the stapes in the fenestra vestibuli causes motion (arrows) in the perilymph in the scala vestibuli. At the apex of the cochlea (the helicotrema), the compression wave in the perilymph passes down the scala tympani, causing a lateral bulging of the secondary tympanic membrane in the fenestra cochleae. C. Movement of the perilymph (arrows) after movement of the base of the stapes. Note the position of the basilar fibers of the basilar membrane.

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    Preganglionic parasympathetic secretomotor fibers that reach the submandibular ganglion and are there relayed to the submandibular and sublingual salivary glands

Tympanic Nerve The tympanic nerve arises from the glossopharyngeal nerve, just below the jugular foramen (see page 765). It passes through the floor of the middle ear and onto the promontory (Fig. 11-30). Here it splits into branches, which form the tympanic plexus. The tympanic plexus supplies the lining of the middle ear and gives off the lesser petrosal nerve, which sends secretomotor fibers to the parotid gland via the otic ganglion (see page 787). It leaves the skull through the foramen ovale and joins the otic ganglion. Clinical Notes Infections and Otitis Media Pathogenic organisms can gain entrance to the middle ear by ascending through the auditory tube from the nasal part of the pharynx. Acute infection of the middle ear (otitis media) produces bulging and redness of the tympanic membrane. Complications of Otitis Media Inadequate treatment of otitis media can result in the spread of the infection into the mastoid antrum and the mastoid air cells (acute mastoiditis). Acute mastoiditis may be followed by the further spread of the organisms beyond the confines of the middle ear. The meninges and the temporal lobe of the brain lie superiorly. A spread of the infection in this direction could produce a meningitis and a cerebral abscess in the temporal lobe. Beyond the medial wall of the middle ear lie the facial nerve and the internal ear. A spread of the infection in this direction can cause a facial nerve palsy and labyrinthitis with vertigo. The posterior wall of the mastoid antrum is related to the sigmoid venous sinus. If the infection spreads in this direction, a thrombosis in the sigmoid sinus may well take place. These various complications emphasize the importance of knowing the anatomy of this region. The Internal Ear, or Labyrinth The labyrinth is situated in the petrous part of the temporal bone, medial to the middle ear (Fig. 11-28). It consists of the bony labyrinth, comprising a series of cavities within the bone, and the membranous labyrinth, comprising a series of membranous sacs and ducts contained within the bony labyrinth. Bony Labyrinth The bony labyrinth consists of three parts: the vestibule, the semicircular canals, and the cochlea (Fig. 11-30). These are cavities situated in the substance of dense bone. They are lined by endosteum and contain a clear fluid, the perilymph, in which is suspended the membranous labyrinth. The vestibule, the central part of the bony labyrinth, lies posterior to the cochlea and anterior to the semicircular canals. In its lateral wall are the fenestra vestibuli, which is closed by the base of the stapes and its anular ligament, and the fenestra cochleae, which is closed by the secondary tympanic membrane. Lodged within the vestibule are the saccule and utricle of the membranous labyrinth (Fig. 11-30). The three semicircular canals—superior, posterior, and lateral—open into the posterior part of the vestibule. Each canal has a swelling at one end called the ampulla. The canals open into the vestibule by five orifices, one of which is common to two of the canals. Lodged within the canals are the semicircular ducts (Fig. 11-30). The superior semicircular canal is vertical and placed at right angles to the long axis of the petrous bone. The posterior canal is also vertical but is placed parallel with the long axis of the petrous bone. The lateral canal is set in a horizontal position, and it lies in the medial wall of the aditus to the mastoid antrum, above the facial nerve canal. The cochlea resembles a snail shell. It opens into the anterior part of the vestibule (Fig. 11-30). Basically, it consists of a central pillar, the modiolus, around which a hollow bony tube makes two and one half spiral turns. Each successive turn is of decreasing radius so that the whole structure is conical. The apex faces anterolaterally and the base faces posteromedially. The first basal turn of the cochlea is responsible for the promontory seen on the medial wall of the middle ear. The modiolus has a broad base, which is situated at the bottom of the internal acoustic meatus. It is perforated by branches of the cochlear nerve. A spiral ledge, the spiral lamina, winds around the modiolus and projects into the interior of the canal and partially divides it. The basilar membrane stretches from the free edge of the spiral lamina to the outer bony wall, thus dividing the cochlear canal into the scala vestibuli above and the scala tympani below. The perilymph within the scala vestibuli is separated from the middle ear by the base of the stapes and the anular ligament at the fenestra vestibuli. The perilymph in the scala tympani is separated from the middle ear by the secondary tympanic membrane at the fenestra cochleae. Membranous Labyrinth The membranous labyrinth is lodged within the bony labyrinth (Fig. 11-30). It is filled with endolymph and surrounded by perilymph. It consists of the utricle and saccule, which are lodged in the bony vestibule; the three semicircular ducts, which lie within the bony semicircular canals; and the duct of the cochlea, which lies within the bony cochlea. All these structures freely communicate with one another. The utricle is the larger of the two vestibular sacs. It is indirectly connected to the saccule and the ductus endolymphaticus by the ductus utriculosaccularis. The saccule is globular and is connected to the utricle, as described previously. The ductus endolymphaticus, after being joined by the ductus utriculosaccularis, passes on to end in a small blind pouch, the saccus endolymphaticus (Fig. 11-30). This lies beneath the dura on the posterior surface of the petrous part of the temporal bone. P.715
Located on the walls of the utricle and saccule are specialized sensory receptors, which are sensitive to the orientation of the head to gravity or other acceleration forces. The semicircular ducts, although much smaller in diameter than the semicircular canals, have the same configuration. They are arranged at right angles to each other so that all three planes are represented. Whenever the head begins or ceases to move, or whenever a movement of the head accelerates or decelerates, the endolymph in the semicircular ducts changes its speed of movement relative to that of the walls of the semicircular ducts. This change is detected in the sensory receptors in the ampullae of the semicircular ducts. The duct of the cochlea is triangular in cross section and is connected to the saccule by the ductus reuniens. The highly specialized epithelium that lies on the basilar membrane forms the spiral organ of Corti and contains the sensory receptors for hearing. For a detailed description of the spiral organ, a textbook of histology should be consulted. Vestibulocochlear Nerve On reaching the bottom of the internal acoustic meatus (see page 765), the nerve divides into vestibular and cochlear portions (Fig. 11-28). The vestibular nerve is expanded to form the vestibular ganglion. The branches of the nerve then pierce the lateral end of the internal acoustic meatus and gain entrance to the membranous labyrinth, where they supply the utricle, the saccule, and the ampullae of the semicircular ducts. The cochlear nerve divides into branches, which enter foramina at the base of the modiolus. The sensory ganglion of this nerve takes the form of an elongated spiral ganglion that is lodged in a canal winding around the modiolus in the base of the spiral lamina. The peripheral branches of this nerve pass from the ganglion to the spiral organ of Corti. The Mandible The mandible or lower jaw is the largest and strongest bone of the face, and it articulates with the skull at the temporomandibular joint. The mandible consists of a horseshoe-shaped body and a pair of rami. The body of the mandible meets the ramus on each side at the angle of the mandible (Fig. 11-32). The body of the mandible, on its external surface in the midline, has a faint ridge indicating the line of fusion of the two halves during development at the symphysis menti. The mental foramen can be seen below the second premolar tooth; it transmits the terminal branches of the inferior alveolar nerve and vessels. On the medial surface of the body of the mandible in the median plane are seen the mental spines; these give origin to the genioglossus muscles above and the geniohyoid muscles below (Fig. 11-31). The mylohyoid line can be seen as an oblique ridge that runs backward and laterally from the area of the mental spines to an area below and behind the third molar tooth. The submandibular fossa, for the superficial part of the submandibular salivary gland, lies below the posterior part of the mylohyoid line. The sublingual fossa, for the sublingual gland, lies above the anterior part of the mylohyoid line (Fig. 11-32). The upper border of the body of the mandible is called the alveolar part; in the adult it contains 16 sockets for the roots of the teeth. The lower border of the body of the mandible is called the base. The digastric fossa is a small, roughened depression on the base, on either side of the symphysis menti (Fig. 11-32). It is in these fossae that the anterior bellies of the digastric muscles are attached. The ramus of the mandible is vertically placed and has an anterior coronoid process and a posterior condyloid process, or head; the two processes are separated by the mandibular notch (Fig. 11-32). On the lateral surface of the ramus are markings for the attachment of the masseter muscle. On the medial surface is the mandibular foramen for the inferior alveolar nerve and vessels. In front of the foramen is a projection of bone, called the lingula, for the attachment of the sphenomandibular ligament (Figs. 11-32 and 11-33). The foramen leads into the mandibular canal, which opens on the lateral surface of the body of the mandible at the mental foramen (see above). The incisive canal is a continuation forward of the mandibular canal beyond the mental foramen and below the incisor teeth. The coronoid process receives on its medial surface the attachment of the temporalis muscle. Below the condyloid process, or head, is a short neck (Fig. 11-32). The important muscles and ligaments attached to the mandible are shown in Figure 11-32. Clinical Notes Fractures of the Mandible The mandible is horseshoe shaped and forms part of a bony ring with the two temporomandibular joints and the base of the skull. Traumatic impact is transmitted around the ring, causing a single fracture or multiple fractures of the mandible, often far removed from the point of impact. Temporomandibular Joint Articulation Articulation occurs between the articular tubercle and the anterior portion of the mandibular fossa of the temporal bone above and the head (condyloid process) of the mandible below (Figs. 11-33 and 11-34). The articular surfaces are covered with fibrocartilage. Type of Joint The temporomandibular joint is synovial. The articular disc divides the joint into upper and lower cavities (Fig. 11-35). Capsule The capsule surrounds the joint and is attached above to the articular tubercle and the margins of the mandibular fossa and below to the neck of the mandible. P.716

Figure 11-32 A. Mandible. B. Hyoid bone.

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Figure 11-33 Temporomandibular joint as seen from the lateral (A) and medial (B) aspects.

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Figure 11-34 A dissection of the left temporomandibular joint. The capsule and lateral temporomandibular ligament have been removed to reveal the interior of the joint. Note the articular tubercle and mandibular fossa of the temporal bone and the head of the mandible. The articular disc is present within the joint cavity on the upper surface of the head of the mandible.

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Figure 11-35 Temporomandibular joint with mouth closed (A) and with the mouth open (B). Note the position of the head of the mandible and articular disc in relation to the articular tubercle in each case. C. The attachment of the muscles of mastication to the mandible. The arrows indicate the direction of their actions.

Ligaments The lateral temporomandibular ligament strengthens the lateral aspect of the capsule, and its fibers run downward and backward from the tubercle on the root of the zygoma to the lateral surface of the neck of the mandible (Fig. 11-33). This ligament limits the movement of the mandible in a posterior direction and thus protects the external auditory meatus. The sphenomandibular ligament lies on the medial side of the joint (Fig. 11-33). It is a thin band that is attached above to the spine of the sphenoid bone and below to the lingula of the mandibular foramen. It represents the remains of the first pharyngeal arch in this region. The stylomandibular ligament lies behind and medial to the joint and some distance from it. It is merely a band of thickened deep cervical fascia that extends from the apex of the styloid process to the angle of the mandible (Fig. 11-33). The articular disc divides the joint into upper and lower cavities (Fig. 11-35). It is an oval plate of fibrocartilage that is P.720
attached circumferentially to the capsule. It is also attached in front to the tendon of the lateral pterygoid muscle and by fibrous bands to the head of the mandible. These bands ensure that the disc moves forward and backward with the head of the mandible during protraction and retraction of the mandible. The upper surface of the disc is concavoconvex from before backward to fit the shape of the articular tubercle and the mandibular fossa; the lower surface is concave to fit the head of the mandible. Synovial Membrane This lines the capsule in the upper and lower cavities of the joint (Fig. 11-35). Nerve Supply Auriculotemporal and masseteric branches of the mandibular nerve Movements The mandible can be depressed or elevated, protruded or retracted. Rotation can also occur, as in chewing. In the position of rest, the teeth of the upper and lower jaws are slightly apart. On closure of the jaws, the teeth come into contact. Depression of the Mandible As the mouth is opened, the head of the mandible rotates on the undersurface of the articular disc around a horizontal axis. To prevent the angle of the jaw impinging unnecessarily on the parotid gland and the sternocleidomastoid muscle, the mandible is pulled forward. This is accomplished by the contraction of the lateral pterygoid muscle, which pulls forward the neck of the mandible and the articular disc so that the latter moves onto the articular tubercle (Fig. 11-35). The forward movement of the disc is limited by the tension of the fibroelastic tissue, which tethers the disc to the temporal bone posteriorly. Depression of the mandible is brought about by contraction of the digastrics, the geniohyoids, and the mylohyoids; the lateral pterygoids play an important role by pulling the mandible forward. Elevation of the Mandible The movements in depression of the mandible are reversed. First, the head of the mandible and the disc move backward, and then the head rotates on the lower surface of the disc. Elevation of the mandible is brought about by contraction of the temporalis, the masseter, and the medial pterygoids. The head of the mandible is pulled backward by the posterior fibers of the temporalis. The articular disc is pulled backward by the fibroelastic tissue, which tethers the disc to the temporal bone posteriorly. Protrusion of the Mandible The articular disc is pulled forward onto the anterior tubercle, carrying the head of the mandible with it. All movement thus takes place in the upper cavity of the joint. In protrusion, the lower teeth are drawn forward over the upper teeth, which is brought about by contraction of the lateral pterygoid muscles of both sides, assisted by both medial pterygoids. Retraction of the Mandible The articular disc and the head of the mandible are pulled backward into the mandibular fossa. Retraction is brought about by contraction of the posterior fibers of the temporalis. Lateral Chewing Movements These are accomplished by alternately protruding and retracting the mandible on each side. For this to take place, a certain amount of rotation occurs, and the muscles responsible on both sides work alternately and not in unison. The muscles of mastication are summarized in Table 11-4. See also Figure 11-35. Important Relations of the Temporomandibular Joint

  • Anteriorly: The mandibular notch and the masseteric nerve and artery (Fig. 11-36)
  • Posteriorly: The tympanic plate of the external auditory meatus (Fig. 11-33) and the glenoid process of the parotid gland
  • Laterally: The parotid gland, fascia, and skin (see Fig. 11-85)
  • Medially: The maxillary artery and vein and the auriculotemporal nerve

Clinical Notes Clinical Significance of the Temporomandibular Joint The temporomandibular joint lies immediately in front of the external auditory meatus. The great strength of the lateral temporomandibular ligament prevents the head of the mandible from passing backward and fracturing the tympanic plate when a severe blow falls on the chin. The articular disc of the temporomandibular joint may become partially detached from the capsule, and this results in its movement becoming noisy and producing an audible click during movements at the joint. Dislocation of the Temporomandibular Joint Dislocation sometimes occurs when the mandible is depressed. In this movement, the head of the mandible and the articular disc both move forward until they reach the summit of the articular tubercle. In this position, the joint is unstable, and a minor blow on the chin or a sudden contraction of the lateral pterygoid muscles, as in yawning, may be sufficient to pull the disc forward beyond the summit. In bilateral cases the mouth is fixed in an open position, and both heads of the mandible lie in front of the articular tubercles. Reduction of the dislocation is easily achieved by pressing the gloved thumbs downward on the lower molar teeth and pushing the jaw backward. The downward pressure overcomes the tension of the temporalis and masseter muscles, and the backward pressure overcomes the spasm of the lateral pterygoid muscles. P.721

Table 11-4 Muscles of the Head

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Figure 11-36 Infratemporal and submandibular regions. Parts of the zygomatic arch, the ramus, and the body of the mandible have been removed to display deeper structures.

The Scalp Structure The scalp consists of five layers, the first three of which are intimately bound together and move as a unit (Fig. 11-37). To assist one in memorizing the names of the five layers of the scalp, use each letter of the word SCALP to denote the layer of the scalp.

  • Skin, which is thick and hair bearing and contains numerous sebaceous glands
  • Connective tissue beneath the skin, which is fibrofatty, the fibrous septa uniting the skin to the underlying aponeurosis of the occipitofrontalis muscle (Fig. 11-37). Numerous arteries and veins are found in this layer. The arteries are branches of the external and internal carotid arteries, and a free anastomosis takes place between them.
  • Aponeurosis (epicranial), which is a thin, tendinous sheet that unites the occipital and frontal bellies of the occipitofrontalis muscle (Figs. 11-37 and 11-38). The lateral margins of the aponeurosis are attached to the temporal fascia. The subaponeurotic space is the potential space P.723
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    beneath the epicranial aponeurosis. It is limited in front and behind by the origins of the occipitofrontalis muscle, and it extends laterally as far as the attachment of the aponeurosis to the temporal fascia.
    Figure 11-37 A. Coronal section of the upper part of the head showing the layers of the scalp, the sagittal suture of the skull, the falx cerebri, the superior and inferior sagittal venous sinuses, the arachnoid granulations, the emissary veins, and the relation of cerebral blood vessels to the subarachnoid space. B. Sensory nerve supply and arterial supply to the scalp.
    Figure 11-38 Muscles of facial expression.
  • Loose areolar tissue, which occupies the subaponeurotic space (Fig. 11-37) and loosely connects the epicranial aponeurosis to the periosteum of the skull (the pericranium). The areolar tissue contains a few small arteries, but it also contains some important emissary veins. The emissary veins are valveless and connect the superficial veins of the scalp with the diploic veins of the skull bones and with the intracranial venous sinuses (Fig. 11-37).
  • Pericranium, which is the periosteum covering the outer surface of the skull bones. It is important to remember that at the sutures between individual skull bones, the periosteum on the outer surface of the bones becomes continuous with the periosteum on the inner surface of the skull bones (Fig. 11-37).

Muscles of the Scalp Occipitofrontalis The origin, insertion, nerve supply, and action of this muscle are described in Table 11-4. Note that when this muscle contracts, the first three layers of the scalp move forward or backward, the loose areolar tissue of the fourth layer of the scalp allowing the aponeurosis to move on the pericranium. The frontal bellies of the occipitofrontalis can raise the eyebrows in expressions of surprise or horror. P.725
Sensory Nerve Supply of the Scalp The main trunks of the sensory nerves lie in the superficial fascia. Moving laterally from the midline anteriorly, the following nerves are present:

  • The supratrochlear nerve, a branch of the ophthalmic division of the trigeminal nerve, winds around the superior orbital margin and supplies the scalp (Fig. 11-37). It passes backward close to the median plane and reaches nearly as far as the vertex of the skull.
  • The supraorbital nerve, a branch of the ophthalmic division of the trigeminal nerve, winds around the superior orbital margin and ascends over the forehead (Fig. 11-37). It supplies the scalp as far backward as the vertex.
  • The zygomaticotemporal nerve, a branch of the maxillary division of the trigeminal nerve, supplies the scalp over the temple (Fig. 11-37).
  • The auriculotemporal nerve, a branch of the mandibular division of the trigeminal nerve, ascends over the side of the head from in front of the auricle (Fig. 11-37). Its terminal branches supply the skin over the temporal region.
  • The lesser occipital nerve, a branch of the cervical plexus (C2), supplies the scalp over the lateral part of the occipital region (Fig. 11-37) and the skin over the medial surface of the auricle.
  • The greater occipital nerve, a branch of the posterior ramus of the second cervical nerve, ascends over the back of the scalp and supplies the skin as far forward as the vertex of the skull (Fig. 11-37).

Arterial Supply of the Scalp The scalp has a rich supply of blood to nourish the hair follicles, and, for this reason, the smallest cut bleeds profusely. The arteries lie in the superficial fascia. Moving laterally from the midline anteriorly, the following arteries are present:

  • The supratrochlear and the supraorbital arteries, branches of the ophthalmic artery, ascend over the forehead in company with the supratrochlear and supraorbital nerves (Fig. 11-37).
  • The superficial temporal artery, the smaller terminal branch of the external carotid artery, ascends in front of the auricle in company with the auriculotemporal nerve (Fig. 11-37). It divides into anterior and posterior branches, which supply the skin over the frontal and temporal regions.
  • The posterior auricular artery, a branch of the external carotid artery, ascends behind the auricle to supply the scalp above and behind the auricle (Fig. 11-37).
  • The occipital artery, a branch of the external carotid artery, ascends from the apex of the posterior triangle, in company with the greater occipital nerve (Fig. 11-37). It supplies the skin over the back of the scalp and reaches as high as the vertex of the skull.

Venous Drainage of the Scalp The supratrochlear and supraorbital veins unite at the medial margin of the orbit to form the facial vein. The superficial temporal vein unites with the maxillary vein in the substance of the parotid gland to form the retromandibular vein (Fig. 11-39). The posterior auricular vein unites with the posterior division of the retromandibular vein, just below the parotid gland, to form the external jugular vein (Fig. 11-39). The occipital vein drains into the suboccipital venous plexus, which lies beneath the floor of the upper part of the posterior triangle; the plexus in turn drains into the vertebral veins or the internal jugular vein. The veins of the scalp freely anastomose with one another and are connected to the diploic veins of the skull bones and the intracranial venous sinuses by the valveless emissary veins (Fig. 11-37). Lymph Drainage of the Scalp Lymph vessels in the anterior part of the scalp and forehead drain into the submandibular lymph nodes (Fig. 11-40). Drainage from the lateral part of the scalp above the ear is into the superficial parotid (preauricular) nodes; lymph vessels in the part of the scalp above and behind the ear drain into the mastoid nodes. Vessels in the back of the scalp drain into the occipital nodes. Clinical Notes Clinical Significance of the Scalp Structure It is important to realize that the skin, the subcutaneous tissue, and the epicranial aponeurosis are closely united to one another and are separated from the periosteum by loose areolar tissue. The skin of the scalp possesses numerous sebaceous glands, the ducts of which are prone to infection and damage by combs. For this reason, sebaceous cysts of the scalp are common. Lacerations of the Scalp The scalp has a profuse blood supply to nourish the hair follicles. Even a small laceration of the scalp can cause severe blood loss. It is often difficult to stop the bleeding of a scalp wound because the arterial walls are attached to fibrous septa in the subcutaneous tissue and are unable to contract or retract to allow blood clotting to take place. Local pressure applied to the scalp is the only satisfactory method of stopping the bleeding (see below). In automobile accidents, it is common for large areas of the scalp to be cut off the head as a person is projected forward through the windshield. Because of the profuse blood supply, it is often possible to replace large areas of scalp that are only hanging to the skull by a narrow pedicle. Suture them in place, and necrosis will not occur. The tension of the epicranial aponeurosis, produced by the tone of the occipitofrontalis muscles, is important in all deep wounds of the scalp. If the aponeurosis has been divided, the wound will gape open. For satisfactory healing to take place, the opening in the aponeurosis must be closed with sutures. Often a wound caused by a blunt object such as a baseball bat closely resembles an incised wound. This is because the scalp is split against the unyielding skull, and the pull of the occipitofrontalis muscles causes a gaping wound. This anatomic fact may be of considerable forensic importance. Life-Threatening Scalp Hemorrhage Anatomically, it is useful to remember in an emergency that all the superficial arteries supplying the scalp ascend from the face and the neck. Thus, in an emergency situation, encircle the head just above the ears and eyebrows with a tie, shoelaces, or even a piece of string and tie it tight. Then insert a pen, pencil, or stick into the loop and rotate it so that the tourniquet exerts pressure on the arteries. Scalp Infections Infections of the scalp tend to remain localized and are usually painful because of the abundant fibrous tissue in the subcutaneous layer. Occasionally, an infection of the scalp spreads by the emissary veins, which are valveless, to the skull bones, causing osteomyelitis. Infected blood in the diploic veins may travel by the emissary veins farther into the venous sinuses and produce venous sinus thrombosis. Blood or pus may collect in the potential space beneath the epicranial aponeurosis. It tends to spread over the skull, being limited in front by the orbital margin, behind by the nuchal lines, and laterally by the temporal lines. On the other hand, subperiosteal blood or pus is limited to one bone because of the attachment of the periosteum to the sutural ligaments. P.726

Figure 11-39 Main veins of the head and neck.

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Figure 11-40 Lymph drainage of the head and neck.

The Face Skin of the Face The skin of the face possesses numerous sweat and sebaceous glands. It is connected to the underlying bones by loose connective tissue, in which are embedded the muscles of facial expression. No deep fascia is present in the face. Wrinkle lines of the face result from the repeated folding of the skin perpendicular to the long axis of the underlying contracting muscles, coupled with the loss of youthful skin elasticity. Surgical scars of the face are less conspicuous if they follow the wrinkle lines. Sensory Nerves of the Face The skin of the face is supplied by branches of the three divisions of the trigeminal nerve, except for the small area over the angle of the mandible and the parotid gland (Fig. 11-41), which is supplied by the great auricular nerve (C2 and 3). The overlap of the three divisions of the trigeminal nerve is slight compared with the considerable overlap of dermatomes of the trunk and limbs. The ophthalmic nerve supplies the region developed from the frontonasal process; the maxillary nerve serves the region developed from the maxillary process of the first pharyngeal arch; and the mandibular nerve serves the region developed from the mandibular process of the first pharyngeal arch. These nerves not only supply the skin of the face, but also supply proprioceptive fibers to the underlying muscles of facial expression. They are, in addition, the sensory nerve supply to the mouth, teeth, nasal cavities, and paranasal air sinuses. Ophthalmic Nerve The ophthalmic nerve supplies the skin of the forehead, the upper eyelid, the conjunctiva, and the side of the nose down P.728
to and including the tip. Five branches of the nerve pass to the skin.

Figure 11-41 A. Sensory nerve supply to the skin of the face. B. Branches of the seventh cranial nerve to muscles of facial expression. C. Arterial supply of the face. D. Venous drainage of the face.
  • The lacrimal nerve supplies the skin and conjunctiva of the lateral part of the upper eyelid (Fig. 11-41).
  • The supraorbital nerve winds around the upper margin of the orbit at the supraorbital notch (Fig. 11-41). It divides into branches that supply the skin and conjunctiva on the central part of the upper eyelid; it also supplies the skin of the forehead.
  • The supratrochlear nerve winds around the upper margin of the orbit medial to the supraorbital nerve (Fig. 11-41). It divides into branches that supply the skin and conjunctiva on the medial part of the upper eyelid and the skin over the lower part of the forehead, close to the median plane.
  • The infratrochlear nerve leaves the orbit below the pulley of the superior oblique muscle. It supplies the skin and conjunctiva on the medial part of the upper eyelid and the adjoining part of the side of the nose (Fig. 11-41).
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  • The external nasal nerve leaves the nose by emerging between the nasal bone and the upper nasal cartilage. It supplies the skin on the side of the nose down as far as the tip (Fig. 11-41).

Maxillary Nerve The maxillary nerve supplies the skin on the posterior part of the side of the nose, the lower eyelid, the cheek, the upper lip, and the lateral side of the orbital opening. Three branches of the nerve pass to the skin.

  • The infraorbital nerve is a direct continuation of the maxillary nerve. It enters the orbit and appears on the face through the infraorbital foramen. It immediately divides into numerous small branches, which radiate out from the foramen and supply the skin of the lower eyelid and cheek, the side of the nose, and the upper lip (Fig. 11-41).
  • The zygomaticofacial nerve passes onto the face through a small foramen on the lateral side of the zygomatic bone. It supplies the skin over the prominence of the cheek (Fig. 11-41).
  • The zygomaticotemporal nerve emerges in the temporal fossa through a small foramen on the posterior surface of the zygomatic bone. It supplies the skin over the temple (Fig. 11-41).

Mandibular Nerve The mandibular nerve supplies the skin of the lower lip, the lower part of the face, the temporal region, and part of the auricle. It then passes upward to the side of the scalp. Three branches of the nerve pass to the skin.

  • The mental nerve emerges from the mental foramen of the mandible and supplies the skin of the lower lip and chin (Fig. 11-41).
  • The buccal nerve emerges from beneath the anterior border of the masseter muscle and supplies the skin over a small area of the cheek (Fig. 11-41).
  • The auriculotemporal nerve ascends from the upper border of the parotid gland between the superficial temporal vessels and the auricle. It supplies the skin of the auricle, the external auditory meatus, the outer surface of the tympanic membrane, and the skin of the scalp above the auricle (Fig. 11-41).

Clinical Notes Sensory Innervation and Trigeminal Neuralgia The facial skin receives its sensory nerve supply from the three divisions of the trigeminal nerve. Remember that a small area of skin over the angle of the jaw is supplied by the great auricular nerve (C2 and 3). Trigeminal neuralgia is a relatively common condition in which the patient experiences excruciating pain in the distribution of the mandibular or maxillary division, with the ophthalmic division usually escaping. A physician should be able to map out accurately on a patient’s face the distribution of each of the divisions of the trigeminal nerve. Arterial Supply of the Face The face receives a rich blood supply from two main vessels: the facial and superficial temporal arteries, which are supplemented by several small arteries that accompany the sensory nerves of the face. The facial artery arises from the external carotid artery (Figs. 11-55 and 11-59). Having arched upward and over the submandibular salivary gland, it curves around the inferior margin of the body of the mandible at the anterior border of the masseter muscle. It is here that the pulse can be easily felt (Fig. 11-135). It runs upward in a tortuous course toward the angle of the mouth and is covered by the platysma and the risorius muscles. It then ascends deep to the zygomaticus muscles and the levator labii superioris muscle and runs along the side of the nose to the medial angle of the eye, where it anastomoses with the terminal branches of the ophthalmic artery (Fig. 11-41). Branches

  • The submental artery arises from the facial artery at the lower border of the body of the mandible. It supplies the skin of the chin and lower lip.
  • The inferior labial artery arises near the angle of the mouth. It runs medially in the lower lip and anastomoses with its fellow of the opposite side.
  • The superior labial artery arises near the angle of the mouth. It runs medially in the upper lip and gives branches to the septum and ala of the nose.
  • The lateral nasal artery arises from the facial artery alongside the nose. It supplies the skin on the side and dorsum of the nose.
  • The superficial temporal artery (Fig. 11-41), the smaller terminal branch of the external carotid artery, commences in the parotid gland. It ascends in front of the auricle to supply the scalp (see page 725).
  • The transverse facial artery, a branch of the superficial temporal artery, arises within the parotid gland. It runs forward across the cheek just above the parotid duct (Fig. 11-41).
  • The supraorbital and supratrochlear arteries, branches of the ophthalmic artery, supply the skin of the forehead (Fig. 11-41).

Clinical Notes Blood Supply of the Facial Skin The blood supply to the skin of the face is profuse so that it is rare in plastic surgery for skin flaps to necrose in this region. Facial Arteries and Taking the Patient’s Pulse The superficial temporal artery, as it crosses the zygomatic arch in front of the ear, and the facial artery, as it winds around the lower margin of the mandible level with the anterior border of the masseter, are commonly used by the anesthetist to take the patient’s pulse. P.730
Venous Drainage of the Face The facial vein is formed at the medial angle of the eye by the union of the supraorbital and supratrochlear veins (Fig. 11-41). It is connected to the superior ophthalmic vein directly through the supraorbital vein. By means of the superior ophthalmic vein, the facial vein is connected to the cavernous sinus (Fig. 11-9); this connection is of great clinical importance because it provides a pathway for the spread of infection from the face to the cavernous sinus. The facial vein descends behind the facial artery to the lower margin of the body of the mandible. It crosses superficial to the submandibular gland and is joined by the anterior division of the retromandibular vein. The facial vein ends by draining into the internal jugular vein. Tributaries The facial vein receives tributaries that correspond to the branches of the facial artery. It is joined to the pterygoid venous plexus by the deep facial vein and to the cavernous sinus by the superior ophthalmic vein.

Figure 11-42 A. Bones of the front of the skull. B. Lymph drainage of the face.

The transverse facial vein joins the superficial temporal vein within the parotid gland. Clinical Notes Facial Infections and Cavernous Sinus Thrombosis The area of facial skin bounded by the nose, the eye, and the upper lip is a potentially dangerous zone to have an infection. For example, a boil in this region can cause thrombosis of the facial vein, with spread of organisms through the inferior ophthalmic veins to the cavernous sinus. The resulting cavernous sinus thrombosis may be fatal unless adequately treated with antibiotics. Lymph Drainage of the Face Lymph from the forehead and the anterior part of the face drains into the submandibular lymph nodes (Fig. 11-42). A P.731
few buccal lymph nodes may be present along the course of these lymph vessels. The lateral part of the face, including the lateral parts of the eyelids, is drained by lymph vessels that end in the parotid lymph nodes. The central part of the lower lip and the skin of the chin are drained into the submental lymph nodes. Bones of the Face The bones that form the front of the skull are shown in Figure 11-42. The superior orbital margins and the area above them are formed by the frontal bone, which contains the frontal air sinuses. The lateral orbital margin is formed by the zygomatic bone and the inferior orbital margin is formed by the zygomatic bone and the maxilla. The medial orbital margin is formed above the maxillary process of the frontal bone and below by the frontal process of the maxilla. The root of the nose is formed by the nasal bones, which articulate below with the maxilla and above with the frontal bones. Anteriorly, the nose is completed by upper and lower plates of hyaline cartilage and small cartilages of the ala nasi. The important central bone of the middle third of the face is the maxilla, containing its teeth and the maxillary air sinus. The bone of the lower third of the face is the mandible, with its teeth. A more detailed account of the bones of the face is given in the discussion of the skull (see page 669). Muscles of the Face (Muscles of Facial Expression) The muscles of the face are embedded in the superficial fascia, and most arise from the bones of the skull and are inserted into the skin (Fig. 11-38). The orifices of the face, namely, the orbit, nose, and mouth, are guarded by the eyelids, nostrils, and lips, respectively. It is the function of the facial muscles to serve as sphincters or dilators of these structures. A secondary function of the facial muscles is to modify the expression of the face. All the muscles of the face are developed from the second pharyngeal arch and are supplied by the facial nerve. Muscles of the Eyelids The sphincter muscle of the eyelids is the orbicularis oculi, and the dilator muscles are the levator palpebrae superioris and the occipitofrontalis (Fig. 11-38). The levator palpebrae superioris is described on page 691. The occipitofrontalis forms part of the scalp and is described on page 724. The origin, insertion, nerve supply, and action of the orbicularis oculi and the corrugator supercilii are described in Table 11-4. Muscles of the Nostrils The sphincter muscle is the compressor naris and the dilator muscle is the dilator naris (Fig. 11-38). The origin, insertion, nerve supply, and action of the compressor naris, the dilator naris, and the procerus are shown in Table 11-4. Muscles of the Lips and Cheeks The sphincter muscle is the orbicularis oris. The dilator muscles consist of a series of small muscles that radiate out from the lips. Sphincter Muscle of the Lips: Orbicularis Oris

  • Origin and insertion: The fibers encircle the oral orifice within the substance of the lips (Fig. 11-38). Some of the fibers arise near the midline from the maxilla above and the mandible below. Other fibers arise from the deep surface of the skin and pass obliquely to the mucous membrane lining the inner surface of the lips. Many of the fibers are derived from the buccinator muscle.
  • Nerve supply: Buccal and mandibular branches of the facial nerve
  • Action: Compresses the lips together

Dilator Muscles of the Lips The dilator muscles (Fig. 11-38) radiate out from the lips, and their action is to separate the lips; this movement is usually accompanied by separation of the jaws. The muscles arise from the bones and fascia around the oral aperture and converge to be inserted into the substance of the lips. Traced from the side of the nose to the angle of the mouth and then below the oral aperture, the muscles are named as follows:

  • Levator labii superioris alaeque nasi
  • Levator labii superioris
  • Zygomaticus minor
  • Zygomaticus major
  • Levator anguli oris (deep to the zygomatic muscles)
  • Risorius
  • Depressor anguli oris
  • Depressor labii inferioris
  • Mentalis

Nerve Supply Buccal and mandibular branches of the facial nerve Muscle of the Cheek Buccinator

  • Origin: From the outer surface of the alveolar margins of the maxilla and mandible opposite the molar teeth and from the pterygomandibular ligament (Fig. 11-38)
  • Insertion: The muscle fibers pass forward, forming the muscle layer of the cheek. The muscle is pierced by the parotid duct. At the angle of the mouth the central fibers decussate, those from below entering the upper lip and those from above entering the lower lip; the highest and lowest fibers continue into the upper and lower lips, respectively, without intersecting. The buccinator muscle thus blends and forms part of the orbicularis oris muscle.
  • Nerve supply: Buccal branch of the facial nerve
  • Action: Compresses the cheeks and lips against the teeth

The origin, insertion, nerve supply, and action of the muscles of the lips and cheeks are shown in Table 11-4. P.732
Clinical Notes Facial Muscle Paralysis The facial muscles are innervated by the facial nerve. Damage to the facial nerve in the internal acoustic meatus (by a tumor), in the middle ear (by infection or operation), in the facial nerve canal (perineuritis, Bell’s palsy), or in the parotid gland (by a tumor) or caused by lacerations of the face will cause distortion of the face, with drooping of the lower eyelid, and the angle of the mouth will sag on the affected side. This is essentially a lower motor neuron lesion. An upper motor neuron lesion (involvement of the pyramidal tracts) will leave the upper part of the face normal because the neurons supplying this part of the face receive corticobulbar fibers from both cerebral cortices. Facial Nerve As the facial nerve runs forward within the substance of the parotid salivary gland (see page XXX), it divides into its five terminal branches (Fig. 11-41).

  • The temporal branch emerges from the upper border of the gland and supplies the anterior and superior auricular muscles, the frontal belly of the occipitofrontalis, the orbicularis oculi, and the corrugator supercilii.
  • The zygomatic branch emerges from the anterior border of the gland and supplies the orbicularis oculi.
  • The buccal branch emerges from the anterior border of the gland below the parotid duct and supplies the buccinator muscle and the muscles of the upper lip and nostril.
    Figure 11-43 Different stages in development of the face.

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    Figure 11-44 Various forms of cleft lip.
    Figure 11-45 Unilateral cleft upper lip. (Courtesy of R. Chase.)
    Figure 11-46 Bilateral cleft upper lip and palate. (Courtesy of R. Chase.)

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    Figure 11-47 Right-sided oblique facial cleft and left-sided cleft upper lip. There also is total bilateral cleft palate. (Courtesy of R. Chase.)
  • The mandibular branch emerges from the anterior border of the gland and supplies the muscles of the lower lip.
  • The cervical branch emerges from the lower border of the gland and passes forward in the neck below the mandible to supply the platysma muscle; it may cross the lower margin of the body of the mandible to supply the depressor anguli oris muscle.

The facial nerve is the nerve of the second pharyngeal arch and supplies all the muscles of facial expression. It does not supply the skin, but its branches communicate with branches of the trigeminal nerve. It is believed that the proprioceptive nerve fibers of the facial muscles leave the facial nerve in these communicating branches and pass to the central nervous system via the trigeminal nerve. A summary of the origin and distribution of the facial nerve is shown in Figure 11-67. Embryologic Notes Development of the Face Early in development, the face of the embryo is represented by an area bounded cranially by the neural plate, caudally by the pericardium, and laterally by the mandibular process of the first pharyngeal arch on each side (Fig. 11-43). In the center of this area is a depression in the ectoderm known as the stomodeum. In the floor of the depression is the buccopharyngeal membrane. By the fourth week, the buccopharyngeal membrane breaks down so that the stomodeum communicates with the foregut. The further development of the face depends on the coming together and fusion of several important processes, namely, the frontonasal process, the maxillary processes, and the mandibular processes (Fig. 11-43). The frontonasal process begins as a proliferation of mesenchyme on the ventral surface of the developing brain, and this grows toward the stomodeum. Meanwhile, the maxillary process grows out from the upper end of each first arch and passes medially, forming the lower border of the developing orbit. The mandibular processes of the first arches now approach one another in the midline below the stomodeum and fuse to form the lower jaw and lower lip (Fig. 11-43). The olfactory pits appear as depressions in the lower edge of the advancing frontonasal process, dividing it into a medial nasal process and two lateral nasal processes. With further development, the maxillary processes grow medially and fuse with the lateral nasal processes and with the medial nasal process (Fig. 11-43). The medial nasal process forms the philtrum of the upper lip and the premaxilla. The maxillary processes extend medially, forming the upper jaw and the cheek, and finally bury the premaxilla and fuse in the midline. The various processes that ultimately form the face unite during the second month. The upper lip is formed by the growth medially of the maxillary processes of the first pharyngeal arch on each side. Ultimately, the maxillary processes meet in the midline and fuse with each other and with the medial nasal process (Fig. 11-43). Thus, the lateral parts of the upper lip are formed from the maxillary processes, and the medial part, or philtrum, from the medial nasal process, with contributions from the maxillary processes. The lower lip is formed from the mandibular process of the first pharyngeal arch on each side (Fig. 11-43). These processes grow medially below the stomodeum and fuse in the midline to form the entire lower lip. Each lip separates from its respective gum as the result of the appearance of a linear thickening of ectoderm, the labiogingival lamina, which grows down into the underlying mesenchyme and later degenerates. A deep groove thus forms between the lips and the gums. In the midline, a short area of the labiogingival lamina remains and tethers each lip to the gum, thus forming the frenulum. At first, the mouth has a broad opening, but later this diminishes in extent because of fusion of the lips at the lateral angles. Sensory Nerve Supply to the Skin of the Developing Face The area of skin overlying the frontonasal process and its derivatives receives its sensory nerve supply from the ophthalmic division of the trigeminal nerve, whereas the maxillary division of the trigeminal nerve supplies the area of skin overlying the maxillary process. The area of skin overlying the mandibular process is supplied by the mandibular division of the trigeminal nerve. Muscles of the Developing Face (Muscles of Facial Expression) The muscles of the face are derived from the mesenchyme of the second pharyngeal arch. The nerve supply of these muscles is the nerve of the second pharyngeal arch—namely, the seventh cranial nerve. Cleft Upper Lip Cleft upper lip may be confined to the lip or may be associated with a cleft palate. The anomaly is usually unilateral cleft lip and is caused by a failure of the maxillary process to fuse with the medial nasal process (Figs. 11-44 and 11-45). Bilateral cleft lip is caused by a failure of both maxillary processes to fuse with the medial nasal process, which then remains as a central flap of tissue (Figs. 11-46 and 11-48). Median cleft upper lip is very rare and is caused by the failure of the rounded swellings of the medial nasal process to fuse in the midline. Oblique Facial Cleft Oblique facial cleft is a rare condition in which the cleft lip on one side extends to the medial margin of the orbit (Figs. 11-44 and 11-47). This is caused by the failure of the maxillary process to fuse with the lateral and medial nasal processes. Cleft Lower Lip Cleft lower lip is a rare condition. The cleft is exactly central and is caused by incomplete fusion of the mandibular processes (Fig. 11-44). Treatment of Isolated Cleft Lip The condition of isolated cleft lip usually is treated by plastic surgery no later than 2 months after birth, provided the baby’s condition permits. The surgeon strives to approximate the vermilion border and to form a normal-looking lip (Fig. 11-48A–C). Macrostomia and Microstomia The normal size of the mouth shows considerable individual variation. Rarely, there is incomplete fusion of the maxillary with the mandibular processes, producing an excessively large mouth or macrostomia. Very rarely, there is excessive fusion of these processes, producing a small mouth or microstomia. These conditions can easily be corrected surgically. P.735
The Neck The neck is the region of the body that lies between the lower margin of the mandible above and the suprasternal notch and the upper border of the clavicle below. It is strengthened by the cervical part of the vertebral column, which is convex forward and supports the skull. Behind the vertebrae is a mass of extensor muscles and in front is a smaller group of flexor muscles (Fig. 11-49). In the central region of the neck are parts of the respiratory system, namely, the larynx and the trachea, and behind are parts of the alimentary system, the pharynx and the esophagus. At the sides of these structures are the vertically running carotid arteries, internal jugular veins, the vagus nerve, and the deep cervical lymph nodes (Fig. 11-49).

Figure 11-48 Cleft lip and palate. A. A three-dimensional ultrasonograph reveals bilateral cleft lip at 22 weeks of gestation. (Courtesy of Dr. B. Benacerraf.) B. An infant with bilateral complete cleft lip and palate. C. Shows the same child at 18 months of age, after synchronous nasolabial repair and palatal closure performed at a second stage. (Courtesy of Dr. J. B. Mulliken. N Engl J Med 351;8:769.)

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Figure 11-49 Cross section of the neck at the level of the sixth cervical vertebra.

Skin of the Neck The natural lines of cleavage of the skin are constant and run almost horizontally around the neck. This is important clinically because an incision along a cleavage line will heal as a narrow scar, whereas one that crosses the lines will heal as a wide or heaped-up scar. Cutaneous Nerves The skin overlying the trapezius muscle on the back of the neck and on the back of the scalp as high as the vertex is supplied segmentally by posterior rami of cervical nerves 2 to 5 (Fig. 11-50). The greater occipital nerve is a branch of the posterior ramus of the second cervical nerve. The first cervical nerve has no cutaneous branch. The skin of the front and sides of the neck is supplied by anterior rami of cervical nerves 2 to 4 through branches of the cervical plexus. The branches emerge from beneath the posterior border of the sternocleidomastoid muscle (Fig. 11-50). The lesser occipital nerve (C2) hooks around the accessory nerve and ascends along the posterior border of the sternocleidomastoid muscle to supply the skin over the lateral part of the occipital region and the medial surface of the auricle (Fig. 11-50). The great auricular nerve (C2 and 3) ascends across the sternocleidomastoid muscle and divides into branches that supply the skin over the angle of the mandible, the parotid gland, and on both surfaces of the auricle (Fig. 11-50). The transverse cutaneous nerve (C2 and 3) emerges from behind the middle of the posterior border of the sternocleidomastoid muscle. It passes forward across that muscle and divides into branches that supply the skin on the anterior and lateral surfaces of the neck, from the body of the mandible to the sternum (Fig. 11-50). The supraclavicular nerves (C3 and 4) emerge from beneath the posterior border of the sternocleidomastoid muscle and descend across the side of the neck. They pass onto the chest wall and shoulder region, down to the level of the second rib (Fig. 11-50). The medial supraclavicular nerve crosses the medial end of the clavicle and supplies the skin as far as the median plane. The intermediate supraclavicular nerve crosses the middle of the clavicle and supplies the skin of the chest wall. The lateral supraclavicular nerve crosses the lateral end of the clavicle and supplies the P.737
skin over the shoulder and the upper half of the deltoid muscle; this nerve also supplies the posterior aspect of the shoulder as far down as the spine of the scapula.

Figure 11-50 Sensory nerve supply to skin of the head and neck. Note that the skin over the angle of the jaw is supplied by the great auricular nerve (C2 and 3) and not by branches of the trigeminal nerve.

Superficial Fascia The superficial fascia of the neck forms a thin layer that encloses the platysma muscle. Also embedded in it are the cutaneous nerves referred to in the previous section, the superficial veins, and the superficial lymph nodes. Platysma The platysma muscle (Figs. 11-38 and 11-51) is a thin but clinically important muscular sheet embedded in the superficial fascia. It is described in Table 11-5, page 742. Superficial Veins External Jugular Vein The external jugular vein begins just behind the angle of the mandible by the union of the posterior auricular vein with the posterior division of the retromandibular vein (Fig. 11-52). It descends obliquely across the sternocleidomastoid muscle and, just above the clavicle in the posterior triangle, pierces the deep fascia and drains into the subclavian vein (Fig. 11-53). It varies considerably in size, and its course extends from the angle of the mandible to the middle of the clavicle. Tributaries The external jugular vein (Fig. 11-52) has the following tributaries:

  • Posterior auricular vein
  • Posterior division of the retromandibular vein
  • Posterior external jugular vein, a small vein that drains the posterior part of the scalp and neck and joins the external jugular vein about halfway along its course
  • Transverse cervical vein
  • Suprascapular vein
  • Anterior jugular vein

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Figure 11-51 Dissection of the anterior aspect of the neck showing the platysma muscles and the lower ends of the sternocleidomastoid muscles on both sides. The skin has been reflected downward.

Clinical Notes Visibility of the External Jugular Vein The external jugular vein is less obvious in children and women because their subcutaneous tissue tends to be thicker than the tissue of men. In obese individuals, the vein may be difficult to identify even when they are asked to hold their breath, which impedes the venous return to the right side of the heart and distends the vein. The superficial veins of the neck tend to be enlarged and often tortuous in professional singers because of prolonged periods of raised intrathoracic pressure. The External Jugular Vein as a Venous Manometer The external jugular vein serves as a useful venous manometer. Normally, when the patient is lying at a horizontal angle of 30°, the level of the blood in the external jugular veins reaches about one third of the way up the neck. As the patient sits up, the blood level falls until it is no longer visible behind the clavicle. External Jugular Vein Catheterization The external jugular vein can be used for catheterization, but the presence of valves or tortuosity may make the passage of the catheter difficult. Because the right external jugular vein is in the most direct line with the superior vena cava, it is the one most commonly used (Fig. 11-54). The vein is catheterized about halfway between the level of the cricoid cartilage and the clavicle. The passage of the catheter should be performed during inspiration when the valves are open. P.739

Figure 11-52 Major superficial veins of the face and neck.

Anterior Jugular Vein The anterior jugular vein begins just below the chin, by the union of several small veins (Fig. 11-52). It runs down the neck close to the midline. Just above the suprasternal notch, the veins of the two sides are united by a transverse trunk called the jugular arch. The vein then turns sharply laterally and passes deep to the sternocleidomastoid muscle to drain into the external jugular vein. Superficial Lymph Nodes The superficial cervical lymph nodes lie along the external jugular vein superficial to the sternocleidomastoid muscle (Fig. 11-40). They receive lymph vessels from the occipital and mastoid lymph nodes (see page 755) and drain into the deep cervical lymph nodes. Bones of the Neck Cervical Vertebrae The cervical part of the vertebral column is described on page 855. Hyoid Bone The hyoid bone is a mobile single bone found in the midline of the neck below the mandible and abides the larynx. It does not articulate with any other bones. The hyoid bone is U shaped and consists of a body and two greater and two lesser cornua (Fig. 11-32). It is attached to the skull by the stylohyoid ligament and to the thyroid cartilage by the thyrohyoid membrane. The hyoid bone forms a base for the tongue and is suspended in position by muscles that connect it to the mandible, to the styloid process of the temporal bone, to the thyroid cartilage, to the sternum, and to the scapula. The important muscles attached to the hyoid bone are shown in Figure 11-32. Muscles of the Neck The superficial muscles of the side of the neck (Figs. 11-38 and 11-51) are described in Table 11-5. The suprahyoid and infrahyoid muscles and the anterior and lateral vertebral muscles are also described in Table 11-5. Clinical Notes Clinical Identification of the Platysma The platysma can be seen as a thin sheet of muscle just beneath the skin by having the patient clench his or her jaws firmly. The muscle extends from the body of the mandible downward over the clavicle onto the anterior chest wall. Platysma Tone and Neck Incisions In lacerations or surgical incisions in the neck it is very important that the subcutaneous layer with the platysma be carefully sutured, since the tone of the platysma can pull on the scar tissue, resulting in broad, unsightly scars. Platysma Innervation, Mouth Distortion, and Neck Incisions The platysma muscle is innervated by the cervical branch of the facial nerve. This nerve emerges from the lower end of the parotid gland and travels forward to the platysma; it then sometimes crosses the lower border of the mandible to supply the depressor anguli oris muscle (see page 765). Skin lacerations over the mandible or upper part of the neck may distort the shape of the mouth. P.740
Key Neck Muscles Sternocleidomastoid Muscle When the sternocleidomastoid muscle (Figs. 11-51, 11-53, and 11-55) contracts, it appears as an oblique band crossing the side of the neck from the sternoclavicular joint to the mastoid process of the skull. It divides the neck into anterior and posterior triangles (Fig. 11-56). The anterior border covers the carotid arteries, the internal jugular vein, and the deep cervical lymph nodes; it also overlaps the thyroid gland. The muscle is covered superficially by skin, fascia, the platysma muscle, and the external jugular vein. The deep surface of the posterior border is related to the cervical plexus of nerves, the phrenic nerve, and the upper part of the brachial plexus. The origin, insertion, nerve supply, and action of the sternocleidomastoid muscle are summarized in Table 11-5.

Figure 11-53 Posterior triangle of the neck.

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Figure 11-54 Catheterization of the right external jugular vein. A. Surface marking of the vein. B. Site of catheterization. Note how the external jugular vein joins the subclavian vein at a right angle. C. Cross section of the neck showing the relationships of the external jugular vein as it crosses the posterior triangle of the neck.

Clinical Notes Sternocleidomastoid Muscle and Protection From Trauma The sternocleidomastoid, a strong, thick muscle crossing the side of the neck, protects the underlying soft structures from blunt trauma. Suicide attempts by cutting one’s throat often fail because the individual first extends the neck before making several horizontal cuts with a knife. Extension of the cervical part of the vertebral column and extension of the head at the atlanto-occipital joint cause the carotid sheath with its contained large blood vessels to slide posteriorly beneath the sternocleidomastoid muscle. To achieve the desired result with the head and neck fully extended, some individuals have to make several attempts and only succeed when the larynx and the greater part of the sternocleidomastoid muscles have been severed. The common sites for the wounds are immediately above and below the hyoid bone. Congenital Torticollis Most cases of congenital torticollis are a result of excessive stretching of the sternocleidomastoid muscle during a difficult labor. Hemorrhage occurs into the muscle and may be detected as a small, rounded “tumor” during the early weeks after birth. Later, this becomes invaded by fibrous tissue, which contracts and shortens the muscle. The mastoid process is thus pulled down toward the sternoclavicular joint of the same side, the cervical spine is flexed, and the face looks upward to the opposite side. If left untreated, asymmetrical growth changes occur in the face, and the cervical vertebrae may become wedge shaped. Spasmodic Torticollis Spasmodic torticollis, which results from repeated chronic contractions of the sternocleidomastoid and trapezius muscles, is usually psychogenic in origin. Section of the spinal part of the accessory nerve may be necessary in severe cases. P.742

Table 11-5 Muscles of the Neck
Muscle Origin Insertion Nerve Supply Action
Platysma Deep fascia over pectoralis major and deltoid Body of mandible and angle of mouth Facial nerve cervical branch Depresses mandible and angle of mouth
Sternocleidomastoid Manubrium sterni and medial third of clavicle Mastoid process of temporal bone and occipital bone Spinal part of accessory nerve and C2 and 3 Two muscles acting together extend head and flex neck; one muscle rotates head to opposite side
Digastric
    Posterior belly Mastoid process of temporal bone Intermediate tendon is held to hyoid by fascial sling Facial nerve Depresses mandible or elevates hyoid bone
    Anterior belly Body of mandible   Nerve to mylohyoid  
Stylohyoid Styloid process Body of hyoid bone Facial nerve Elevates hyoid bone
Mylohyoid Mylohyoid line of body of mandible Body of hyoid bone and fibrous raphe Inferior alveolar nerve Elevates floor of mouth and hyoid bone or depresses mandible
Geniohyoid Inferior mental spine of mandible Body of hyoid bone First cervical nerve Elevates hyoid bone or depresses mandible
Sternohyoid Manubrium sterni and clavicle Body of hyoid bone Ansa cervicalis; C1, 2, and 3 Depresses hyoid bone
Sternothyroid Manubrium sterni Oblique line on lamina of thyroid cartilage Ansa cervicalis; C1, 2, and 3 Depresses larynx
Thyrohyoid Oblique line on lamina of thyroid cartilage Lower border of body of hyoid bone First cervical nerve Depresses hyoid bone or elevates larynx
Omohyoid
    Inferior belly Upper margin of scapula and suprascapular ligament Intermediate tendon is held to clavicle and first rib by fascial sling Ansa cervicalis; C1, 2, and 3 Depresses hyoid bone
    Superior belly Lower border of body of hyoid bone      
Scalenus anterior Transverse processes of third, fourth, fifth, and sixth cervical vertebrae First rib C4, 5, and 6 Elevates first rib; laterally flexes and rotates cervical part of vertebral column
Scalenus medius Transverse processes of upper six cervical vertebrae First rib Anterior rami of cervical nerves Elevates first rib; laterally flexes and rotates cervical part of vertebral column
Scalenus posterior Transverse processes of lower cervical vertebrae Second rib Anterior rami of cervical nerves Elevates second rib; laterally flexes and rotates cervical part of vertebral column

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Figure 11-55 Anterior triangle of the neck.

Scalenus Anterior Muscle The scalenus anterior muscle is a key muscle in understanding the root of the neck (Fig. 11-57). It is deeply placed and it descends almost vertically from the vertebral column to the first rib. Important Relations

  • Anteriorly: Related to the carotid arteries, the vagus nerve, the internal jugular vein, and the deep cervical lymph nodes (Fig. 11-49). The transverse cervical and suprascapular arteries and the prevertebral layer of deep cervical fascia bind the phrenic nerve to the muscle.
  • Posteriorly: Related to the pleura, the origin of the brachial plexus, and the second part of the subclavian artery (Fig. 11-57). The scalenus medius muscle lies behind the scalenus anterior muscle.
  • Medially: Related to the vertebral artery and vein and the sympathetic trunk (Fig. 11-57). On the left side, the medial border is related to the thoracic duct.
  • Laterally: Related to the emerging branches of the cervical plexus, the roots of the brachial plexus, and the third part of the subclavian artery (Fig. 11-57)

The origin, insertion, nerve supply, and action of the scalenus anterior muscle are summarized in Table 11-5. Deep Cervical Fascia The deep cervical fascia supports the muscles, the vessels, and the viscera of the neck (Fig. 11-49). In certain areas, it is condensed to form well-defined, fibrous sheets called the investing layer, the pretracheal layer, and the prevertebral layer. It is also condensed to form the carotid sheath (Fig. 11-49). P.744

Figure 11-56 Muscular triangles of the neck.

Investing Layer The investing layer is a thick layer that encircles the neck. It splits to enclose the trapezius and the sternocleidomastoid muscles (Fig. 11-49). Pretracheal Layer The pretracheal layer is a thin layer that is attached above to the laryngeal cartilages (Fig. 11-49). It surrounds the thyroid and the parathyroid glands, forming a sheath for them, and encloses the infrahyoid muscles. Prevertebral Layer The prevertebral layer is a thick layer that passes like a septum across the neck behind the pharynx and the esophagus and in front of the prevertebral muscles and the vertebral column (Fig. 11-49). It forms the fascial floor of the posterior triangle, and it extends laterally over the first rib into the axilla to form the important axillary sheath (see page 747). Clinical Notes Clinical Significance of the Deep Fascia of the Neck As previously described, the deep fascia in certain areas forms distinct sheets called the investing, pretracheal, and prevertebral layers. These fascial layers are easily recognizable to the surgeon at operation. Fascial Spaces Between the more dense layers of deep fascia in the neck is loose connective tissue that forms potential spaces that are clinically important. Among the more important spaces are the visceral, retropharyngeal, submandibular, and masticatory spaces (Fig. 11-58). The deep fascia and the fascial spaces are important because organisms originating in the mouth, teeth, pharynx, and esophagus can spread among the fascial planes and spaces, and the tough fascia can determine the direction of spread of infection and the path taken by pus. It is possible for blood, pus, or air in the retropharyngeal space to spread downward into the superior mediastinum of the thorax. Acute Infections of the Fascial Spaces of the Neck Dental infections most commonly involve the lower molar teeth. The infection spreads medially from the mandible into the submandibular and masticatory spaces and pushes the tongue forward and upward. Further spread downward may involve the visceral space and lead to edema of the vocal cords and airway obstruction. Ludwig’s angina is an acute infection of the submandibular fascial space and is commonly secondary to dental infection. Chronic Infection of the Fascial Spaces of the Neck Tuberculous infection of the deep cervical lymph nodes can result in liquefaction and destruction of one or more of the nodes. The pus is at first limited by the investing layer of the deep fascia. Later, this becomes eroded at one point, and the pus passes into the less restricted superficial fascia. A dumbbell or collar-stud abscess is now present. The clinician is aware of the superficial abscess but must not forget the existence of the deeply placed abscess. P.745

Figure 11-57 Prevertebral region and the root of the neck.

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Figure 11-58 A. Cross section of the neck showing the visceral space. B. Sagittal section of the neck showing the positions of the retropharyngeal and submandibular spaces. C. Vertical section of the body of the mandible close to the angle showing the masticatory space.

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Carotid Sheath The carotid sheath is a local condensation of the prevertebral, the pretracheal, and the investing layers of the deep fascia that surround the common and internal carotid arteries, the internal jugular vein, the vagus nerve, and the deep cervical lymph nodes (Fig. 11-49). Axillary Sheath All the anterior rami of the cervical nerves that emerge in the interval between the scalenus anterior and scalenus medius muscles lie at first deep to the prevertebral fascia. As the subclavian artery and the brachial plexus emerge in the interval between the scalenus anterior and the scalenus medius muscles, they carry with them a sheath of the fascia, which extends into the axilla and is called the axillary sheath. Cervical Ligaments

  • Stylohyoid ligament: Connects the styloid process to the lesser cornu of the hyoid bone (Fig. 11-80)
  • Stylomandibular ligament: Connects the styloid process to the angle of the mandible (Fig. 11-33)
  • Sphenomandibular ligament: Connects the spine of the sphenoid bone to the lingula of the mandible (Fig. 11-33)
  • Pterygomandibular ligament: Connects the hamular process of the medial pterygoid plate to the posterior end of the mylohyoid line of the mandible. It gives attachment to the superior constrictor and the buccinator muscles (Fig. 11-80).

Muscular Triangles of the Neck The sternocleidomastoid muscle divides the neck into the anterior and the posterior triangles (Fig. 11-56). Anterior Triangle The anterior triangle is bounded above by the body of the mandible, posteriorly by the sternocleidomastoid muscle, and anteriorly by the midline (Fig. 11-56). It is further subdivided into the carotid triangle, the digastric triangle, the submental triangle, and the muscular triangle (Fig. 11-56). Posterior Triangle The posterior triangle is bounded posteriorly by the trapezius muscle, anteriorly by the sternocleidomastoid muscle, and inferiorly by the clavicle (Fig. 11-56). The posterior triangle of the neck is further subdivided by the inferior belly of the omohyoid muscle into a large occipital triangle above and a small supraclavicular triangle below (Fig. 11-56). The suprahyoid and infrahyoid muscles and the anterior and lateral vertebral muscles are described in Table 11-5. Arteries of the Head and Neck Common Carotid Artery The right common carotid artery arises from the brachiocephalic artery behind the right sternoclavicular joint (Figs. 11-57 and 11-59). The left artery arises from the arch of the aorta in the superior mediastinum (see page 125). The common carotid artery runs upward through the neck under cover of the anterior border of the sternocleidomastoid muscle, from the sternoclavicular joint to the upper border of the thyroid cartilage. Here it divides into the external and internal carotid arteries (Figs. 11-55 and 11-60). Carotid Sinus At its point of division, the terminal part of the common carotid artery or the beginning of the internal carotid artery shows a localized dilatation, called the carotid sinus (Fig. 11-60). The tunica media of the sinus is thinner than elsewhere, but the adventitia is relatively thick and contains numerous nerve endings derived from the glossopharyngeal nerve. The carotid sinus serves as a reflex pressoreceptor mechanism: A rise in blood pressure causes a slowing of the heart rate and vasodilatation of the arterioles. Clinical Notes Carotid Sinus Hypersensitivity In cases of carotid sinus hypersensitivity, pressure on one or both carotid sinuses can cause excessive slowing of the heart rate, a fall in blood pressure, and cerebral ischemia with fainting. Carotid Body The carotid body is a small structure that lies posterior to the point of bifurcation of the common carotid artery (Fig. 11-60). It is innervated by the glossopharyngeal nerve. The carotid body is a chemoreceptor, being sensitive to excess carbon dioxide and reduced oxygen tension in the blood. Such a stimulus reflexly produces a rise in blood pressure and heart rate and an increase in respiratory movements. The common carotid artery is embedded in a connective tissue sheath, called the carotid sheath, throughout its course and is closely related to the internal jugular vein and vagus nerve (Fig. 11-49). Relations of the Common Carotid Artery

  • Anterolaterally: The skin, the fascia, the sternocleidomastoid, the sternohyoid, the sternothyroid, and the superior belly of the omohyoid (Fig. 11-55)
  • Posteriorly: The transverse processes of the lower four cervical vertebrae, the prevertebral muscles, and the sympathetic trunk (Fig. 11-57). In the lower part of the neck are the vertebral vessels.
  • Medially: The larynx and pharynx and, below these, the trachea and esophagus (Fig. 11-49). The lobe of the thyroid gland also lies medially.
  • Laterally: The internal jugular vein and, posterolaterally, the vagus nerve (Fig. 11-49)

Branches of the Common Carotid Artery Apart from the two terminal branches, the common carotid artery gives off no branches. P.748

Figure 11-59 Main arteries of the head and neck. Note that for clarity the thyrocervical trunk, the costocervical trunk, and the internal thoracic artery—branches of the subclavian artery—are not shown.

Clinical Notes Taking the Carotid Pulse The bifurcation of the common carotid artery into the internal and external carotid arteries can be easily palpated just beneath the anterior border of the sternocleidomastoid muscle at the level of the superior border of the thyroid cartilage. This is a convenient site to take the carotid pulse. External Carotid Artery The external carotid artery is one of the terminal branches of the common carotid artery (Fig. 11-59). It supplies structures in the neck, face, and scalp; it also supplies the tongue and the maxilla. The artery begins at the level of the upper border of the thyroid cartilage and terminates in the substance of the parotid gland behind the neck of the mandible by dividing into the superficial temporal and maxillary arteries. Close to its origin, the artery emerges from undercover of the sternocleidomastoid muscle, where its pulsations can be felt. At first, it lies medial to the internal carotid artery, but as it ascends in the neck, it passes backward and lateral to it. It is crossed by the posterior belly of the digastric and the stylohyoid (Fig. 11-55). Relations of the External Carotid Artery

  • Anterolaterally: The artery is overlapped at its beginning by the anterior border of the sternocleidomastoid. Above this level, the artery is comparatively superficial, being covered by skin and fascia. It is crossed by the hypoglossal nerve (Fig. 11-55), the posterior belly of the digastric muscle, and the stylohyoid muscles. Within the parotid gland, it is crossed by the facial nerve (Fig. 11-85). The internal jugular vein first lies lateral to the artery and then posterior to it.
  • Medially: The wall of the pharynx and the internal carotid artery. The stylopharyngeus muscle, the glossopharyngeal nerve, and the pharyngeal branch of the vagus pass between the external and internal carotid arteries (Fig. 11-60).

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Figure 11-60 Styloid muscles, vessels, and nerves of the neck.

For the relations of the external carotid artery in the parotid gland, see Figure 11-85B. Branches of the External Carotid Artery

  • Superior thyroid artery
  • Ascending pharyngeal artery
  • Lingual artery
  • Facial artery
  • Occipital artery
  • Posterior auricular artery
  • Superficial temporal artery
  • Maxillary artery

Superior Thyroid Artery The superior thyroid artery curves downward to the upper pole of the thyroid gland (Figs. 11-55 and 11-60). It is accompanied by the external laryngeal nerve, which supplies the cricothyroid muscle. Ascending Pharyngeal Artery The ascending pharyngeal artery ascends along and supplies the pharyngeal wall. Lingual Artery The lingual artery loops upward and forward and supplies the tongue (Figs. 11-55 and 11-60). Facial Artery The facial artery loops upward close to the outer surface of the pharynx and the tonsil. It lies deep to the submandibular salivary gland and emerges and bends around the lower border of the mandible. It then ascends over the P.750
face close to the anterior border of the masseter muscle. The artery then ascends around the lateral margin of the mouth and terminates at the medial angle of the eye (Figs. 11-55 and 11-59). Branches of the facial artery supply the tonsil, the submandibular salivary gland, and the muscles and the skin of the face. Occipital Artery The artery supplies the back of the scalp (Fig. 11-59). Posterior Auricular Artery The posterior auricular artery supplies the auricle and the scalp (Fig. 11-59). Superficial Temporal Artery The superficial temporal artery ascends over the zygomatic arch, where it may be palpated just in front of the auricle (Fig. 11-59). It is accompanied by the auriculotemporal nerve, and it supplies the scalp. Maxillary Artery The maxillary artery runs forward medial to the neck of the mandible (Fig. 11-59) and enters the pterygopalatine fossa of the skull. Branches of the Maxillary Artery Branches supply the upper and the lower jaws, the muscles of mastication, the nose, the palate, and the meninges inside the skull. Middle Meningeal Artery The middle meningeal artery enters the skull through the foramen spinosum (Fig. 11-66). It runs laterally within the skull and divides into anterior and posterior branches (Figs. 11-20 and 11-131). The anterior branch is important because it lies close to the motor area of the cerebral cortex of the brain. Accompanied by its vein, it grooves (or tunnels) through the upper part of the greater wing of the sphenoid bone of the skull and the thin anteroinferior angle of the parietal bone, where it is prone to damage after a blow to the head. The origin and distribution of the branches of the external carotid artery are shown in Figure 11-59. Internal Carotid Artery The internal carotid artery begins at the bifurcation of the common carotid artery at the level of the upper border of the thyroid cartilage (Figs. 11-55 and 11-59). It supplies the brain, the eye, the forehead, and part of the nose. The artery ascends in the neck embedded in the carotid sheath with the internal jugular vein and vagus nerve. At first it lies superficially; it then passes deep to the parotid salivary gland (Figs. 11-60 and 11-85B). The internal carotid artery leaves the neck by passing into the cranial cavity through the carotid canal in the petrous part of the temporal bone. It then passes upward and forward in the cavernous venous sinus (without communicating with it). The artery then leaves the sinus and passes upward again medial to the anterior clinoid process of the sphenoid bone. The internal carotid artery then inclines backward, lateral to the optic chiasma, and terminates by dividing into the anterior and the middle cerebral arteries. Relations of the Internal Carotid Artery in the Neck

  • Anterolaterally: Below the digastric lie the skin, the fascia, the anterior border of the sternocleidomastoid, and the hypoglossal nerve (Fig. 11-55). Above the digastric lie the stylohyoid muscle, the stylopharyngeus muscle, the glossopharyngeal nerve, the pharyngeal branch of the vagus, the parotid gland, and the external carotid artery (Figs. 11-60 and 11-85B).
  • Posteriorly: The sympathetic trunk (Fig. 11-60), the longus capitis muscle, and the transverse processes of the upper three cervical vertebrae
  • Medially: The pharyngeal wall and the superior laryngeal nerve
  • Laterally: The internal jugular vein and the vagus nerve

Clinical Notes Arteriosclerosis of the Internal Carotid Artery Extensive arteriosclerosis of the internal carotid artery in the neck can cause visual impairment or blindness in the eye on the side of the lesion because of insufficient blood flow through the retinal artery. Motor paralysis and sensory loss may also occur on the opposite side of the body because of insufficient blood flow through the middle cerebral artery. Branches of the Internal Carotid Artery There are no branches in the neck. Many important branches, however, are given off in the skull. Ophthalmic Artery The ophthalmic artery arises from the internal carotid artery as it emerges from the cavernous sinus (Fig. 11-20). It passes forward into the orbital cavity through the optic canal, and it gives off the central artery of the retina, which enters the optic nerve and runs forward to enter the eyeball. The central artery is an end artery and the only blood supply to the retina. Posterior Communicating Artery The posterior communicating artery runs backward to join the posterior cerebral artery (Fig. 11-15). Anterior Cerebral Artery The anterior cerebral artery is a terminal branch of the internal carotid artery (Fig. 11-15). It passes forward between the cerebral hemispheres and then winds around the corpus callosum of the brain to supply the medial and the superolateral surfaces of the cerebral hemisphere. It is joined to the artery of the opposite side by the anterior communicating artery. Middle Cerebral Artery The middle cerebral artery is the largest terminal branch of the internal carotid artery (Fig. 11-15), and it runs laterally in P.751
the lateral cerebral sulcus of the brain. It supplies the entire lateral surface of the cerebral hemisphere except the narrow strip along the superolateral margin (which is supplied by the anterior cerebral artery) and the occipital pole and inferolateral surface of the hemisphere (both of which are supplied by the posterior cerebral artery). The middle cerebral artery thus supplies all the motor area of the cerebral cortex except the leg area. It also gives off central branches that supply central masses of gray matter and the internal capsule of the brain. Circle of Willis The circle of Willis lies in the subarachnoid space (see page 683) at the base of the brain. It is formed by the anastomosis between the branches of the two internal carotid arteries and the two vertebral arteries (Fig. 11-15). The anterior communicating, posterior cerebral, and basilar (formed by the junction of the two vertebral arteries) are all arteries that contribute to the circle. Cortical and central branches arise from the circle and supply the brain. Subclavian Arteries Right Subclavian Artery The right subclavian artery arises from the brachiocephalic artery, behind the right sternoclavicular joint (Figs. 11-57 and 11-59). It arches upward and laterally over the pleura and between the scalenus anterior and medius muscles. At the outer border of the first rib, it becomes the axillary artery. Left Subclavian Artery The left subclavian artery arises from the arch of the aorta in the thorax. It ascends to the root of the neck and then arches laterally in a manner similar to that of the right subclavian artery (Fig. 11-57). The scalenus anterior muscle passes anterior to the artery on each side and divides it into three parts. First Part of the Subclavian Artery The first part of the subclavian artery extends from the origin of the subclavian artery to the medial border of the scalenus anterior muscle (Fig. 11-57). This part gives off the vertebral artery, the thyrocervical trunk, and the internal thoracic artery. Branches The vertebral artery ascends in the neck through the foramina in the transverse processes of the upper six cervical vertebrae (Fig. 11-57). It passes medially above the posterior arch of the atlas and then ascends through the foramen magnum into the skull. On reaching the anterior surface of the medulla oblongata of the brain at the level of the lower border of the pons, it joins the vessel of the opposite side to form the basilar artery. The basilar artery (Fig. 11-15) ascends in a groove on the anterior surface of the pons. It gives off branches to the pons, the cerebellum, and the internal ear. It finally divides into the two posterior cerebral arteries. On each side, the posterior cerebral artery (Fig. 11-15) curves laterally and backward around the midbrain. Cortical branches supply the inferolateral surfaces of the temporal lobe and the visual cortex on the lateral and the medial surfaces of the occipital lobe.

  • Branches in the neck: Spinal and muscular arteries
  • Branches in the skull: Meningeal, anterior and posterior spinal, posterior inferior cerebellar, medullary arteries

The thyrocervical trunk is a short trunk that gives off three terminal branches (Fig. 11-57). The inferior thyroid artery ascends to the posterior surface of the thyroid gland, where it is closely related to the recurrent laryngeal nerve. It supplies the thyroid and the inferior parathyroid glands. The superficial cervical artery is a small branch that crosses the brachial plexus (Fig. 11-57). The suprascapular artery runs laterally over the brachial plexus and follows the suprascapular nerve onto the back of the scapula (Fig. 11-57). The internal thoracic artery descends into the thorax behind the first costal cartilage and in front of the pleura (Fig. 11-57). It descends vertically one fingerbreadth lateral to the sternum; in the sixth intercostal space, it divides into the superior epigastric and the musculophrenic arteries. Second Part of the Subclavian Artery The second part of the subclavian artery lies behind the scalenus anterior muscle (Fig. 11-57). Branches The costocervical trunk runs backward over the dome of the pleura and divides into the superior intercostal artery, which supplies the first and the second intercostal spaces, and the deep cervical artery, which supplies the deep muscles of the neck. Third Part of the Subclavian Artery The third part of the subclavian artery extends from the lateral border of the scalenus anterior muscle (Fig. 11-57) across the posterior triangle of the neck to the lateral border of the first rib, where it becomes the axillary artery. Here, in the root of the neck, it is closely related to the nerves of the brachial plexus. Branches The third part of the subclavian artery usually has no branches. Occasionally, however, the superficial cervical arteries, the suprascapular arteries, or both arise from this part. Clinical Notes Palpation and Compression of the Subclavian Artery in Patients With Upper Limb Hemorrhage In severe traumatic accidents to the upper limb involving laceration of the brachial or axillary arteries, it is important to remember that the hemorrhage can be stopped by exerting strong pressure downward and backward on the third part of the subclavian artery. The use of a blunt object to exert the pressure is of great help, and the artery is compressed against the upper surface of the first rib. P.752
Veins of the Head and Neck The veins of the head and neck may be divided into:

  • The veins of the brain, venous sinuses, diploic veins, and emissary veins
  • The veins of the scalp, face, and neck

Veins of the Brain The veins of the brain are thin walled and have no valves. They consist of the cerebral veins, the cerebellar veins, and the veins of the brainstem, all of which drain into the neighboring venous sinuses. Venous Sinuses The venous sinuses are situated between the periosteal and the meningeal layer of the dura mater (Fig. 11-37A; see also page 686). They have thick, fibrous walls, but they possess no valves. They receive tributaries from the brain, the skull bones, the orbit, and the internal ear. The venous sinuses include the superior and inferior sagittal sinuses, the straight sinus, the transverse sinuses, the sigmoid sinuses, the occipital sinus, the cavernous sinuses, and the superior and inferior petrosal sinuses (Fig. 11-9). All these sinuses are described on page 686 and 687. Diploic Veins The diploic veins occupy channels within the bones of the vault of the skull (Fig. 11-9). Emissary Veins The emissary veins are valveless veins that pass through the skull bones (Fig. 11-9). They connect the veins of the scalp to the venous sinuses (and are an important route for the spread of infection). Veins of the Face and the Neck Facial Vein The facial vein is formed at the medial angle of the eye by the union of the supraorbital and supratrochlear veins (Fig. 11-39). It is connected through the ophthalmic veins with the cavernous sinus. The facial vein descends down the face with the facial artery and passes around the lateral side of the mouth. It then crosses the mandible, is joined by the anterior division of the retromandibular vein, and drains into the internal jugular vein. Superficial Temporal Vein The superficial temporal vein is formed on the side of the scalp (Fig. 11-39). It follows the superficial temporal artery and the auriculotemporal nerve and then enters the parotid salivary gland, where it joins the maxillary vein to form the retromandibular vein. Maxillary Vein The maxillary vein is formed in the infratemporal fossa from the pterygoid venous plexus (Fig. 11-39). The maxillary vein joins the superficial temporal vein to form the retromandibular vein. Retromandibular Vein The retromandibular vein is formed by the union of the superficial temporal and the maxillary veins (Fig. 11-39). On leaving the parotid salivary gland, it divides into an anterior branch, which joins the facial vein, and a posterior branch, which joins the posterior auricular vein to form the external jugular vein. External Jugular Vein The external jugular vein is formed behind the angle of the jaw by the union of the posterior auricular vein with the posterior division of the retromandibular vein (Fig. 11-39). It descends across the sternocleidomastoid muscle and beneath the platysma muscle, and it drains into the subclavian vein behind the middle of the clavicle. Tributaries

  • Posterior external jugular vein from the back of the scalp
  • Transverse cervical vein from the skin and the fascia over the posterior triangle
  • Suprascapular vein from the back of the scapula
  • Anterior jugular vein

Anterior Jugular Vein The anterior jugular vein descends in the front of the neck close to the midline (Fig. 11-39). Just above the sternum, it is joined to the opposite vein by the jugular arch. The anterior jugular vein joins the external jugular vein deep to the sternocleidomastoid muscle. Internal Jugular Vein The internal jugular vein is a large vein that receives blood from the brain, face, and neck (Fig. 11-39). It starts as a continuation of the sigmoid sinus and leaves the skull through the jugular foramen. It then descends through the neck in the carotid sheath lateral to the vagus nerve and the internal and common carotid arteries. It ends by joining the subclavian vein behind the medial end of the clavicle to form the brachiocephalic vein (Figs. 11-39 and 11-57). Throughout its course, it is closely related to the deep cervical lymph nodes. The vein has a dilatation at its upper end called the superior bulb and another near its termination called the inferior bulb. Directly above the inferior bulb is a bicuspid valve. Relations of the Internal Jugular Vein

  • Anterolaterally: The skin, the fascia, the sternocleidomastoid, and the parotid salivary gland. Its lower part is covered by the sternothyroid, sternohyoid, and omohyoid muscles, which intervene between the vein and the sternocleidomastoid (Fig. 11-55). Higher up, it is crossed by the stylohyoid, the posterior belly of the digastric, and the spinal part of the accessory nerve. The chain of deep cervical lymph nodes runs alongside the vein.
  • Posteriorly: The transverse processes of the cervical vertebrae, the levator scapulae, the scalenus medius, the scalenus anterior, the cervical plexus, the phrenic nerve, P.753
    the thyrocervical trunk, the vertebral vein, and the first part of the subclavian artery (Fig. 11-57). On the left side it passes in front of the thoracic duct.
  • Medially: Above lie the internal carotid artery and the 9th, 10th, 11th, and 12th cranial nerves. Below lie the common carotid artery and the vagus nerve.

Tributaries of the Internal Jugular Vein

  • Inferior petrosal sinus (Fig. 11-30)
  • Facial vein (Fig. 11-39)
  • Pharyngeal veins
  • Lingual vein
  • Superior thyroid vein (Fig. 11-55)
  • Middle thyroid vein (Fig. 11-110)

Clinical Notes Penetrating Wounds of the Internal Jugular Vein The hemorrhage of low-pressure venous blood into the loose connective tissue beneath the investing layer of deep cervical fascia may present as a large, slowly expanding hematoma. Air embolism is a serious complication of a lacerated wall of the internal jugular vein. Because the wall of this large vein contains little smooth muscle, its injury is not followed by contraction and retraction (as occurs with arterial injuries). Moreover, the adventitia of the vein wall is attached to the deep fascia of the carotid sheath, which hinders the collapse of the vein. Blind clamping of the vein is prohibited because the vagus and hypoglossal nerves are in the vicinity. Internal Jugular Vein Catheterization The internal jugular vein is remarkably constant in position. It descends through the neck from a point halfway between the tip of the mastoid process and the angle of the jaw to the sternoclavicular joint. Above, it is overlapped by the anterior border of the sternocleidomastoid muscle, and below, it is covered laterally by this muscle. Just above the sternoclavicular joint the vein lies beneath a skin depression between the sternal and clavicular heads of the sternocleidomastoid muscle. In the posterior approach, the tip of the needle and the catheter are introduced into the vein about two fingerbreadths above the clavicle at the posterior border of the sternocleidomastoid muscle (Fig. 11-61). In the anterior approach, with the patient’s head turned to the opposite side, the triangle formed by the sternal and clavicular heads of the sternocleidomastoid muscle and the medial end of the clavicle are identified. A shallow skin depression usually overlies the triangle. The needle and catheter are inserted into the vein at the apex of the triangle in a caudal direction (Fig. 11-61). Subclavian Vein The subclavian vein is a continuation of the axillary vein at the outer border of the first rib (Fig. 11-57). It joins the internal jugular vein to form the brachiocephalic vein, and it receives the external jugular vein. In addition, it often receives the thoracic duct on the left side and the right lymphatic duct on the right. Relations

  • Anteriorly: The clavicle
  • Posteriorly: The scalenus anterior muscle and the phrenic nerve
  • Inferiorly: The upper surface of the first rib

Clinical Notes Subclavian Vein Thrombosis Spontaneous thrombosis of the subclavian and/or axillary veins occasionally occurs after excessive and unaccustomed use of the arm at the shoulder joint. The close relationship of these veins to the first rib and the clavicle and the possibility of repeated minor trauma from these structures is probably a factor in its development. Secondary thrombosis of subclavian and/or axillary veins is a common complication of an indwelling venous catheter. Rarely, the condition may follow a radical mastectomy with a block dissection of the lymph nodes of the axilla. Persistent pain, heaviness, or edema of the upper limb, especially after exercise, is a complication of this condition. Anatomy of Subclavian Vein Catheterization The subclavian vein is located in the lower anterior corner of the posterior triangle of the neck (Fig. 11-62), where it lies immediately posterior to the medial third of the clavicle. Infraclavicular Approach Since the subclavian vein lies close to the undersurface of the medial third of the clavicle (Fig. 11-62), this is a relatively safe site for catheterization. The vein is slightly more medially placed on the left side than on the right side. Anatomy of Procedure The needle should be inserted through the skin just below the lower border of the clavicle at the junction of the medial third and outer two thirds, coinciding with the posterior border of the origin of the clavicular head of the sternocleidomastoid muscle on the upper border of the clavicle (Fig. 11-62). The needle pierces the following structures:

  • Skin
  • Superficial fascia
  • Pectoralis major muscle (clavicular head)
  • Clavipectoral fascia and subclavius muscle
  • Wall of subclavian vein

The needle is pointed upward and posteriorly toward the middle of the suprasternal notch. Anatomy of Problems

  • Hitting the clavicle: The needle may be “walked” along the lower surface of the clavicle until its posterior edge is reached.
  • Hitting the first rib: The needle may hit the first rib, if the needle is pointed downward and not upward.
  • Hitting the subclavian artery: A pulsatile resistance and bright red blood flow indicate that the needle has passed posterior to the scalenus anterior muscle and perforated the subclavian artery.

Anatomy of Complications Refer to Figure 11-62.

  • Pneumothorax: The needle may pierce the cervical dome of the pleura, permitting air to enter the pleural cavity. This complication is more common in children, in whom the pleural reflection is higher than in adults.
  • Hemothorax: The catheter may pierce the posterior wall of the subclavian vein and the pleura.
  • Subclavian artery puncture: The needle pierces the wall of the artery during its insertion.
  • Internal thoracic artery injury: Hemorrhage may occur into the superior mediastinum.
  • Diaphragmatic paralysis: This occurs when the needle damages the phrenic nerve.

The Procedure in Children The needle pierces the skin in the deltopectoral groove about 2 cm from the clavicle. The catheter is tunneled beneath the skin to enter the subclavian vein at the point where the clavicle and the first rib cross. The more oblique approach in children minimizes the possibility of entering the subclavian artery. Supraclavicular Approach This approach (Fig. 11-62) is preferred by many for the following anatomic reasons.

  • The site of penetration of the vein wall is larger, since it lies at the junction of the internal jugular vein and the subclavian vein, which makes the procedure easier.
  • The needle is pointed downward and medially toward the mediastinum, away from the pleura, avoiding the complication of pneumothorax.
  • The catheter is inserted along a more direct course into the brachiocephalic vein and superior vena cava.

Anatomy of the Procedure With the patient in the Trendelenburg position (patient supine with head tilted downward) or simple supine position and the head turned to the opposite side, the posterior border of the clavicular origin of sternocleidomastoid muscle is palpated (Fig. 11-62). The needle is inserted through the skin at the site where the posterior border of the clavicular origin of sternocleidomastoid is attached to the upper border of the clavicle. At this point, the needle lies lateral to the lateral border of scalenus anterior muscle and above the first rib. The needle pierces the following structures (Fig. 11-62):

  • Skin
  • Superficial fascia and platysma
  • Investing layer of deep cervical fascia
  • Wall of the subclavian vein

The needle is directed downward in the direction of the opposite nipple. The needle enters the junction of the internal jugular vein and the subclavian vein. It is important that the operator understands that the pleura is not being penetrated and that it is possible for the needle to lie in a zone between the chest wall and the cervical dome of the parietal pleura but outside the pleural space (cavity). Anatomic Complications The following complications may occur as the result of damage to neighboring anatomic structures (Fig. 11-62):

  • Paralysis of the diaphragm: This is caused by injury to the phrenic nerve as it descends posterior to the internal jugular vein on the surface of the scalenus anterior muscle.
  • Pneumothorax or hemothorax: This is caused by damage to the pleura and/or internal thoracic artery by the needle passing posteriorly and downward.
  • Brachial plexus injury: This is caused by the needle passing posteriorly into the roots or trunks of the plexus.

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Lymph Drainage of the Head and Neck The lymph nodes of the head and neck (Fig. 11-40) are arranged as a regional collar that extends from below the chin to the back of the head and as a deep vertical terminal group that is embedded in the carotid sheath in the neck (Fig. 11-55). Regional Nodes The regional nodes are arranged as follows:

  • Occipital nodes: These are situated over the occipital bone on the back of the skull. They receive lymph from the back of the scalp.
  • Retroauricular (mastoid) nodes: These lie behind the ear over the mastoid process. They receive lymph from the scalp above the ear, the auricle, and the external auditory meatus.
  • Parotid nodes: These are situated on or within the parotid salivary gland. They receive lymph from the scalp above the parotid gland, the eyelids, the parotid gland, the auricle, and the external auditory meatus.
  • Buccal (facial) nodes: One or two nodes lie in the cheek over the buccinator muscle. They drain lymph that ultimately passes into the submandibular nodes.
  • Submandibular nodes: These lie superficial to the submandibular salivary gland just below the lower margin of the jaw. They receive lymph from the front of the scalp; the nose; the cheek; the upper lip and the lower lip (except the central part); the frontal, maxillary, and ethmoid sinuses; the upper and lower teeth (except the lower incisors); the anterior two thirds of the tongue (except the tip); the floor of the mouth and vestibule; and the gums. P.755
    Figure 11-61 Catheterization of the right internal jugular vein. A. Posterior approach. Note the position of the catheter relative to the sternocleidomastoid muscle and the common carotid artery. B. Anterior approach. Note that the catheter is inserted into the vein close to the apex of the triangle formed by the sternal and clavicular heads of the sternocleidomastoid muscle and the clavicle.
  • Submental nodes: These lie in the submental triangle just below the chin. They drain lymph from the tip of the tongue, the floor of the anterior part of the mouth, the incisor teeth, the center part of the lower lip, and the skin over the chin.
  • Anterior cervical nodes: These lie along the course of the anterior jugular veins in the front of the neck. They receive lymph from the skin and superficial tissues of the front of the neck.
  • Superficial cervical nodes: These lie along the course of the external jugular vein on the side of the neck. They drain lymph from the skin over the angle of the jaw, the skin over the lower part of the parotid gland, and the lobe of the ear.
  • Retropharyngeal nodes: These lie behind the pharynx and in front of the vertebral column. They receive lymph from the nasal pharynx, the auditory tube, and the vertebral column.
  • Laryngeal nodes: These lie in front of the larynx. They receive lymph from the larynx.
  • Tracheal (paratracheal) nodes: These lie alongside the trachea. They receive lymph from neighboring structures, including the thyroid gland.

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Figure 11-62 Subclavian vein catheterization. A. Infraclavicular approach. Note the many important anatomic structures located in this region. B. Supraclavicular approach. The catheter enters the subclavian vein close to its junction with the internal jugular vein to form the brachiocephalic vein.

Deep Cervical Nodes The deep cervical nodes form a vertical chain along the course of the internal jugular vein within the carotid sheath (Fig. 11-49). They receive lymph from all the groups of regional nodes. The jugulodigastric node, which is located below and behind the angle of the jaw, is mainly concerned with drainage of the tonsil and the tongue. The jugulo-omohyoid node, which is situated close to the omohyoid muscle, is mainly associated with drainage of the tongue. The efferent lymph vessels from the deep cervical lymph nodes join to form the jugular trunk, which drains into the thoracic duct or the right lymphatic duct (Fig. 11-40). Clinical Notes Clinical Significance of the Cervical Lymph Nodes Knowledge of the lymph drainage of an organ or region is of great clinical importance. Examination of a patient may reveal an enlarged lymph node. It is the physician’s responsibility to determine the cause and be knowledgeable about the area of the body that drains its lymph into a particular node. For example, an enlarged submandibular node can be caused by a pathologic condition in the scalp, the face, the maxillary sinus, or the tongue. An infected tooth of the upper or lower jaw may be responsible. Often a physician has to search systematically the various areas known to drain into a node to discover the cause. Examination of the Deep Cervical Lymph Nodes Lymph nodes in the neck should be examined from behind the patient. The examination is made easier by asking the patient to flex the neck slightly to reduce the tension of the muscles. The groups of nodes should be examined in a definite order to avoid omitting any. After the identification of enlarged lymph nodes, possible sites of infection or neoplastic growth should be examined, including the face, scalp, tongue, mouth, tonsil, and pharynx. Carcinoma Metastases in the Deep Cervical Lymph Node In the head and neck, all the lymph ultimately drains into the deep cervical group of nodes. Secondary carcinomatous deposits in these nodes are common. The primary growth may be easy to find. On the other hand, at certain anatomic sites the primary growth may be small and overlooked, for example, in the larynx, the pharynx, the cervical part of the esophagus, and the external auditory meatus. The bronchi, breast, and stomach are sometimes the site of the primary tumor. In these cases, the secondary growth has spread far beyond the local lymph nodes. When cervical metastases occur, the surgeon usually decides to perform a block dissection of the cervical nodes. This procedure involves the removal en bloc of the internal jugular vein, the fascia, the lymph nodes, and the submandibular salivary gland. The aim of the operation is removal of all the lymph tissues on the affected side of the neck. The carotid arteries and the vagus nerve are carefully preserved. It is often necessary to sacrifice the hypoglossal and vagus nerves, which may be involved in the cancerous deposits. In patients with bilateral spread, a bilateral block dissection may be necessary. An interval of 3 to 4 weeks is necessary before removing the second internal jugular vein. P.757
Cranial Nerves Organization of the Cranial Nerves The cranial nerves are named as follows:

  • I. Olfactory
  • II. Optic
  • III. Oculomotor
  • IV. Trochlear
  • V. Trigeminal
  • VI. Abducent
  • VII. Facial
  • VIII. Vestibulocochlear
  • IX. Glossopharyngeal
  • X. Vagus
  • XI. Accessory
  • XII. Hypoglossal

The olfactory, optic, and vestibulocochlear nerves are entirely sensory; the oculomotor, trochlear, abducent, accessory, and hypoglossal nerves are entirely motor; and the remaining nerves are mixed. The different components of the cranial nerves, their functions, and the openings in the skull through which the nerves leave the cranial cavity are summarized in Table 11-6. Olfactory Nerves The olfactory nerves arise from olfactory receptor nerve cells in the olfactory mucous membrane. The olfactory mucous membrane is situated in the upper part of the nasal cavity above the level of the superior concha (Fig. 11-63). Bundles of these olfactory nerve fibers pass through the openings of the cribriform plate of the ethmoid bone to enter the olfactory bulb in the cranial cavity. The olfactory bulb is connected to the olfactory area of the cerebral cortex by the olfactory tract. Optic Nerve The optic nerve is composed of the axons of the cells of the ganglionic layer of the retina. The optic nerve emerges from the back of the eyeball and leaves the orbital cavity through the optic canal to enter the cranial cavity (Fig. 11-11). The optic nerve then unites with the optic nerve of the opposite side to form the optic chiasma (Fig. 11-63). In the chiasma, the fibers from the medial half of each retina cross the midline and enter the optic tract of the opposite side, whereas the fibers from the lateral half of each retina pass posteriorly in the optic tract of the same side. Most of the fibers of the optic tract terminate by synapsing with nerve cells in the lateral geniculate body (Fig. 11-63). A few fibers pass to the pretectal nucleus and the superior colliculus and are concerned with light reflexes. The axons of the nerve cells of the lateral geniculate body pass posteriorly as the optic radiation and terminate in the visual cortex of the cerebral hemisphere (Fig. 11-63). Oculomotor Nerve The oculomotor nerve emerges on the anterior surface of the midbrain (Fig. 11-64). It passes forward between the posterior cerebral and superior cerebellar arteries (Fig. 11-11). It then continues into the middle cranial fossa in the lateral wall of the cavernous sinus. Here, it divides into a superior and an inferior ramus, which enter the orbital cavity through the superior orbital fissure (Fig. 11-18). The oculomotor nerve supplies the following:

  • The extrinsic muscles of the eye: the levator palpebrae superioris, superior rectus, medial rectus, inferior rectus, and inferior oblique (Fig. 11-64; see also Figs. 11-18 and 11-19)
  • The intrinsic muscles of the eye: the constrictor pupillae of the iris and the ciliary muscles are supplied by the parasympathetic component of the oculomotor nerve. These fibers synapse in the ciliary ganglion and reach the eyeball in the short ciliary nerves (Fig. 11-19).

The oculomotor nerve, therefore, is entirely motor. It is responsible for lifting the upper eyelid; turning the eye upward, downward, and medially; constricting the pupil; and accommodation of the eye. P.758

Table 11-6 Cranial Nerves
Nerve   Components Function Opening in Skull
I. Olfactory Sensory Smell Openings in cribriform plate of ethmoid
II. Optic Sensory Vision Optic canal
III. Oculomotor Motor Lifts upper eyelid, turns eyeball upward, downward, and medially; constricts pupil; accommodates eye Superior orbital fissure
IV. Trochlear Motor Assists in turning eyeball downward and laterally Superior orbital fissure
V. Trigeminal
  Ophthalmic division Sensory Cornea, skin of forehead, scalp, eyelids, and nose; also mucous membrane of paranasal sinuses and nasal cavity Superior orbital fissure
  Maxillary division Sensory Skin of face over maxilla and the upper lip; teeth of upper jaw; mucous membrane of nose, the maxillary air sinus, and palate Foramen rotundum
  Mandibular division Motor Muscles of mastication, mylohyoid, anterior belly of digastric, tensor veli palatini, and tensor tympani Foramen ovale
    Sensory Skin of cheek, skin over mandible, lower lip, and side of head; teeth of lower jaw and temporomandibular joint; mucous membrane of mouth and anterior two thirds of tongue  
VI. Abducent Motor Lateral rectus muscle: turns eyeball laterally Superior orbital fissure
VII. Facial Motor Muscles of face, cheek, and scalp; stapedius muscle of middle ear; stylohyoid; and posterior belly of digastric Internal acoustic meatus, facial canal, stylomastoid foramen
    Sensory Taste from anterior two thirds of tongue, floor of mouth, and palate  
    Secretomotor Submandibular and sublingual salivary parasympathetic glands, lacrimal gland, and glands of nose and palate  
VIII. Vestibulocochlear
  Vestibular Sensory Position and movement of head Internal acoustic meatus
  Cochlear Sensory Hearing  
IX. Glossopharyngeal Motor Stylopharyngeus muscle: assists swallowing  
    Secretomotor parasympathetic Parotid salivary gland Jugular foramen
    Sensory General sensation and taste from posterior third of tongue and pharynx; carotid sinus and carotid body  
X. Vagus Motor Constrictor muscles of pharynx and intrinsic muscles of larynx; involuntary muscle of trachea and bronchi, heart, alimentary tract from pharynx to splenic flexure of colon; liver and pancreas Jugular foramen
    Sensory Taste from epiglottis and vallecula and afferent fibers from structures named above  
XI. Accessory
  Cranial root Motor Muscles of soft palate, pharynx, and larynx Jugular foramen
  Spinal root Motor Sternocleidomastoid and trapezius muscles  
XII. Hypoglossal Motor Muscles of tongue controlling its shape and movement (except palatoglossus) Hypoglossal canal

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Figure 11-63 A. Distribution of the olfactory nerves on the nasal septum and the lateral wall of the nose. B. The optic nerve and its connections.

Trochlear Nerve The trochlear nerve is the most slender of the cranial nerves. Having crossed the nerve of the opposite side, it leaves the posterior surface of the midbrain (Fig. 11-64). It then passes forward through the middle cranial fossa in the lateral wall of the cavernous sinus and enters the orbit through the superior orbital fissure (Figs. 11-11 and 11-18). The trochlear nerve supplies:

  • The superior oblique muscle of the eyeball (extrinsic muscle) (Fig. 11-20)
  • The trochlear nerve is entirely motor and assists in turning the eye downward and laterally.

Trigeminal Nerve The trigeminal nerve is the largest cranial nerve (Fig. 11-65). It leaves the anterior aspect of the pons as a small motor root and a large sensory root, and it passes forward, out of the posterior cranial fossa, to reach the apex of the petrous part of the temporal bone in the middle cranial fossa. Here, the large sensory root expands to form the trigeminal ganglion (Figs. 11-11 and 11-65). The trigeminal ganglion lies within a pouch of dura mater called the trigeminal cave. The motor root of the trigeminal nerve is situated below the sensory ganglion and is completely separate from it. The ophthalmic (V1), maxillary (V2), and mandibular (V3) nerves arise from the anterior border of the ganglion (Figs. 11-11 and 11-65). P.760

Figure 11-64 A. Origin and distribution of the oculomotor nerve. B. Origin and distribution of the trochlear nerve.

Ophthalmic Nerve (V1) The ophthalmic nerve is purely sensory (Figs. 11-65 and 11-50). It runs forward in the lateral wall of the cavernous sinus in the middle cranial fossa and divides into three branches, the lacrimal, frontal, and nasociliary nerves, which enter the orbital cavity through the superior orbital fissure. Branches The lacrimal nerve runs forward on the upper border of the lateral rectus muscle (Fig. 11-18). It is joined by the zygomaticotemporal branch of the maxillary nerve, which contains the parasympathetic secretomotor fibers to the lacrimal gland. The lacrimal nerve then enters the lacrimal gland and gives branches to the conjunctiva and the skin of the upper eyelid. The frontal nerve runs forward on the upper surface of the levator palpebrae superioris muscle and divides into the supraorbital and supratrochlear nerves (Fig. 11-20). These nerves leave the orbital cavity and supply the frontal air sinus and the skin of the forehead and the scalp. The nasociliary nerve crosses the optic nerve, runs forward on the upper border of the medial rectus muscle (Fig. 11-20), and continues as the anterior ethmoid nerve through the anterior ethmoidal foramen to enter the cranial cavity. It then descends through a slit at the side of the crista galli to enter the nasal cavity. It gives off two internal nasal branches and it then supplies the skin of the tip of the nose with the external nasal nerve. Its branches include the following:

  • Sensory fibers to the ciliary ganglion (Fig. 11-20)
  • Long ciliary nerves that contain sympathetic fibers to the dilator pupillae muscle and sensory fibers to the cornea (Fig. 11-20)
  • Infratrochlear nerve that supplies the skin of the eyelids
  • Posterior ethmoidal nerve that is sensory to the ethmoid and sphenoid sinuses

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Figure 11-65 A. Distribution of the trigeminal nerve. B. Origin and distribution of the abducent nerve.

Maxillary Nerve (V2) The maxillary nerve arises from the trigeminal ganglion in the middle cranial fossa. It passes forward in the lateral wall of the cavernous sinus and leaves the skull through the foramen rotundum (Fig. 11-11) and crosses the pterygopalatine fossa to enter the orbit through the inferior orbital fissure (Fig. 11-19). It then continues as the infraorbital nerve in the infraorbital groove, and it emerges on the face through the infraorbital foramen. It gives sensory fibers to the skin of the face and the side of the nose. Branches

  • Meningeal branches
  • Zygomatic branch (Fig. 11-19), which divides into the zygomaticotemporal P.762
    and the zygomaticofacial nerves that supply the skin of the face. The zygomaticotemporal branch gives parasympathetic secretomotor fibers to the lacrimal gland via the lacrimal nerve.
  • Ganglionic branches, which are two short nerves that suspend the pterygopalatine ganglion in the pterygopalatine fossa (Fig. 11-19). They contain sensory fibers that have passed through the ganglion from the nose, the palate, and the pharynx. They also contain postganglionic parasympathetic fibers that are going to the lacrimal gland.
  • Posterior superior alveolar nerve (Fig. 11-19), which supplies the maxillary sinus as well as the upper molar teeth and adjoining parts of the gum and the cheek
  • Middle superior alveolar nerve (Fig. 11-19), which supplies the maxillary sinus as well as the upper premolar teeth, the gums, and the cheek
  • Anterior superior alveolar nerve (Fig. 11-19), which supplies the maxillary sinus as well as the upper canine and the incisor teeth

Pterygopalatine Ganglion The pterygopalatine ganglion is a parasympathetic ganglion, which is suspended from the maxillary nerve in the pterygopalatine fossa (Fig. 11-19). It is secretomotor to the lacrimal and nasal glands (see page 694). Branches

  • Orbital branches, which enter the orbit through the inferior orbital fissure
  • Greater and lesser palatine nerves (Fig. 11-19), which supply the palate, the tonsil, and the nasal cavity
  • Pharyngeal branch, which supplies the roof of the nasopharynx

Mandibular Nerve (V3) The mandibular nerve is both motor and sensory (Figs. 11-11 and 11-65). The sensory root leaves the trigeminal ganglion and passes out of the skull through the foramen ovale to enter the infratemporal fossa. The motor root of the trigeminal nerve also leaves the skull through the foramen ovale and joins the sensory root to form the trunk of the mandibular nerve, and then divides into a small anterior and a large posterior division (Fig. 11-66). Branches From the Main Trunk of the Mandibular Nerve

  • Meningeal branch
  • Nerve to the medial pterygoid muscle, which supplies not only the medial pterygoid, but also the tensor veli palatini muscle.

Branches From the Anterior Division of the Mandibular Nerve

  • Masseteric nerve to the masseter muscle (Fig. 11-36)
  • Deep temporal nerves to the temporalis muscle (Fig. 11-36)
  • Nerve to the lateral pterygoid muscle
  • Buccal nerve to the skin and the mucous membrane of the cheek (Fig. 11-36). The buccal nerve does not supply the buccinator muscle (which is supplied by the facial nerve), and it is the only sensory branch of the anterior division of the mandibular nerve.

Branches From the Posterior Division of the Mandibular Nerve

  • Auriculotemporal nerve, which supplies the skin of the auricle (Fig. 11-66), the external auditory meatus, the temporomandibular joint, and the scalp. This nerve also conveys postganglionic parasympathetic secretomotor fibers from the otic ganglion to the parotid salivary gland.
  • Lingual nerve, which descends in front of the inferior alveolar nerve and enters the mouth (Figs. 11-36 and 11-66). It then runs forward on the side of the tongue and crosses the submandibular duct. In its course, it is joined by the chorda tympani nerve (Figs. 11-36 and 11-66), and it supplies the mucous membrane of the anterior two thirds of the tongue and the floor of the mouth. It also gives off preganglionic parasympathetic secretomotor fibers to the submandibular ganglion.
  • Inferior alveolar nerve (Figs. 11-36 and 11-66), which enters the mandibular canal to supply the teeth of the lower jaw and emerges through the mental foramen (mental nerve) to supply the skin of the chin (Fig. 11-50). Before entering the canal, it gives off the mylohyoid nerve (Fig. 11-36), which supplies the mylohyoid muscle and the anterior belly of the digastric muscle.
  • Communicating branch, which frequently runs from the inferior alveolar nerve to the lingual nerve

The branches of the posterior division of the mandibular nerve are sensory (except the nerve to the mylohyoid muscle). Clinical Notes Injury to the Lingual Nerve The lingual nerve passes forward into the submandibular region from the infratemporal fossa by running beneath the origin of the superior constrictor muscle, which is attached to the posterior border of the mylohyoid line on the mandible. Here, it is closely related to the last molar tooth and is liable to be damaged in cases of clumsy extraction of an impacted third molar. Otic Ganglion The otic ganglion is a parasympathetic ganglion that is located medial to the mandibular nerve just below the skull, and it is adherent to the nerve to the medial pterygoid muscle. The preganglionic fibers originate in the glossopharyngeal nerve, and they reach the ganglion via the lesser petrosal nerve (see page 765). The postganglionic secretomotor fibers reach the parotid salivary gland via the auriculotemporal nerve. Submandibular Ganglion The submandibular ganglion is a parasympathetic ganglion that lies deep to the submandibular salivary gland and is attached to the lingual nerve by small nerves (Figs. 11-36 and 11-66). Preganglionic parasympathetic fibers reach the ganglion P.763
from the facial nerve via the chorda tympani and the lingual nerves. Postganglionic secretomotor fibers pass to the submandibular and the sublingual salivary glands.

Figure 11-66 Infratemporal and submandibular regions. Parts of the zygomatic arch, the ramus, and the body of the mandible have been removed. Mylohyoid and lateral pterygoid muscles have also been removed to display deeper structures. The outline of the sublingual gland is shown as a solid black wavy line.

The trigeminal nerve is thus the main sensory nerve of the head and innervates the muscles of mastication. It also tenses the soft palate and the tympanic membrane. Abducent Nerve This small nerve emerges from the anterior surface of the hindbrain between the pons and the medulla oblongata (Figs. 11-11 and 11-65). It passes forward with the internal carotid artery through the cavernous sinus in the middle cranial fossa and enters the orbit through the superior orbital fissure (Fig. 11-18). The abducent nerve supplies the lateral rectus muscle (Fig. 11-65) and is therefore responsible for turning the eye laterally. Facial Nerve The facial nerve has a motor root and a sensory root (nervus intermedius) (Fig. 11-67). The nerve emerges on P.764
the anterior surface of the hindbrain between the pons and the medulla oblongata. The roots pass laterally in the posterior cranial fossa with the vestibulocochlear nerve and enter the internal acoustic meatus in the petrous part of the temporal bone (Fig. 11-28). At the bottom of the meatus, the nerve enters the facial canal that runs laterally through the inner ear. On reaching the medial wall of the middle ear (tympanic cavity), the nerve swells to form the sensory geniculate ganglion (Fig. 11-67; see also Figs. 11-29 and 11-30). The nerve then bends sharply backward above the promontory and, at the posterior wall of the middle ear, bends down on the medial side of the aditus of the mastoid antrum (see page 712). The nerve descends behind the pyramid and it emerges from the temporal bone through the stylomastoid foramen. The facial nerve now passes forward through the parotid gland to its distribution (Fig. 11-67).

Figure 11-67 A. Distribution of the facial nerve. B. Branches of the facial nerve within the petrous part of the temporal bone; the taste fibers are shown in black. The glossopharyngeal nerve is also shown.

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Important Branches of the Facial Nerve

  • Greater petrosal nerve arises from the nerve at the geniculate ganglion (Fig. 11-67). It contains preganglionic parasympathetic fibers that synapse in the pterygopalatine ganglion. The postganglionic fibers are secretomotor to the lacrimal gland and the glands of the nose and the palate. The greater petrosal nerve also contains taste fibers from the palate.
  • Nerve to stapedius supplies the stapedius muscle in the middle ear (Fig. 11-67).
  • Chorda tympani arises from the facial nerve in the facial canal in the posterior wall of the middle ear (Fig. 11-67). It runs forward over the medial surface of the upper part of the tympanic membrane (Fig. 11-29) and leaves the middle ear through the petrotympanic fissure, thus entering the infratemporal fossa and joining the lingual nerve. The chorda tympani contains preganglionic parasympathetic secretomotor fibers to the submandibular and the sublingual salivary glands. It also contains taste fibers from the anterior two thirds of the tongue and floor of the mouth.
  • Posterior auricular, the posterior belly of the digastric, and the stylohyoid nerves (Fig. 11-67) are muscular branches given off by the facial nerve as it emerges from the stylomastoid foramen.
  • Five terminal branches to the muscles of facial expression. These are the temporal, the zygomatic, the buccal, the mandibular, and the cervical branches (Fig. 11-67).

The facial nerve lies within the parotid salivary gland (Fig. 11-85B) after leaving the stylomastoid foramen, and it is located between the superficial and the deep parts of the gland (see page 787). Here, it gives off the terminal branches that emerge from the anterior border of the gland and pass to the muscles of the face and the scalp. The buccal branch supplies the buccinator muscle, and the cervical branch supplies the platysma and the depressor anguli oris muscles. The facial nerve thus controls facial expression, salivation, and lacrimation and is a pathway for taste sensation from the anterior part of the tongue and floor of the mouth and from the palate. Vestibulocochlear Nerve The vestibulocochlear nerve is a sensory nerve that consists of two sets of fibers: vestibular and cochlear. They leave the anterior surface of the brain between the pons and the medulla oblongata (Fig. 11-68). They cross the posterior cranial fossa and enter the internal acoustic meatus with the facial nerve (Fig. 11-28). Vestibular Fibers The vestibular fibers are the central processes of the nerve cells of the vestibular ganglion situated in the internal acoustic meatus (Fig. 11-68). The vestibular fibers originate from the vestibule and the semicircular canals; therefore, they are concerned with the sense of position and with movement of the head. Cochlear Fibers The cochlear fibers are the central processes of the nerve cells of the spiral ganglion of the cochlea (Fig. 11-68). The cochlear fibers originate in the spiral organ of Corti and are therefore concerned with hearing. Glossopharyngeal Nerve The glossopharyngeal nerve is a motor and sensory nerve (Fig. 11-68). It emerges from the anterior surface of the medulla oblongata between the olive and the inferior cerebellar peduncle. It passes laterally in the posterior cranial fossa and leaves the skull by passing through the jugular foramen. The superior and inferior sensory ganglia are located on the nerve as it passes through the foramen. The glossopharyngeal nerve then descends through the upper part of the neck to the back of the tongue (Fig. 11-68). Important Branches of the Glossopharyngeal Nerve

  • Tympanic branch passes to the tympanic plexus in the middle ear (Fig. 11-68). Preganglionic parasympathetic fibers for the parotid salivary gland now leave the plexus as the lesser petrosal nerve, and they synapse in the otic ganglion.
  • Carotid branch contains sensory fibers from the carotid sinus (pressoreceptor mechanism for the regulation of blood pressure and the carotid body and chemoreceptor mechanism for the regulation of heart rate and respiration) (Fig. 11-68).
  • Nerve to the stylopharyngeus muscle
  • Pharyngeal branches (Fig. 11-68) run to the pharyngeal plexus and also receive branches from the vagus nerve and the sympathetic trunk.
  • Lingual branch (Fig. 11-68) passes to the mucous membrane of the posterior third of the tongue (including the vallate papillae).

The glossopharyngeal nerve thus assists swallowing and promotes salivation. It also conducts sensation from the pharynx and the back of the tongue and carries impulses, which influence the arterial blood pressure and respiration, from the carotid sinus and carotid body. Vagus Nerve The vagus nerve is composed of motor and sensory fibers (Fig. 11-69). It emerges from the anterior surface of the medulla oblongata between the olive and the inferior cerebellar peduncle. The nerve passes laterally through the posterior cranial fossa and leaves the skull through the jugular foramen. The vagus nerve has both superior and inferior sensory ganglia. Below the inferior ganglion, the cranial root of the accessory nerve joins the vagus nerve and is distributed mainly in its pharyngeal and recurrent laryngeal branches. The vagus nerve descends through the neck alongside the carotid arteries and internal jugular vein within the carotid sheath (Fig. 11-49). It passes through the mediastinum of the thorax (Fig. 11-69), passing behind the root of the lung, and enters the abdomen through the esophageal opening in the diaphragm. P.766

Figure 11-68 A. Origin and distribution of the vestibulocochlear nerve. B. Distribution of the glossopharyngeal nerve.

Important Branches of the Vagus Nerve in the Neck

  • Meningeal and auricular branches
  • Pharyngeal branch contains nerve fibers from the cranial part of the accessory nerve. This branch joins the pharyngeal plexus and supplies all the muscles of the pharynx (except the stylopharyngeus) and of the soft palate (except the tensor veli palatini).
  • Superior laryngeal nerve (Fig. 11-69) divides into the internal and the external laryngeal nerves. The internal laryngeal nerve is sensory to the mucous membrane of the piriform fossa and the larynx down as far as the vocal cords. The external laryngeal nerve is motor and is located close to the superior thyroid artery; it supplies the cricothyroid muscle. P.767
    Figure 11-69 Distribution of the vagus nerve.
  • Recurrent laryngeal nerve (Fig. 11-69). On the right side, the nerve hooks around the first part of the subclavian artery and then ascends in the groove between the trachea and the esophagus. On the left side, the nerve hooks around the arch of the aorta and then ascends into the neck between the trachea and the esophagus. The nerve is closely related to the inferior thyroid artery, and it supplies all the muscles of the larynx, except the cricothyroid muscle, the mucous membrane of the larynx below the vocal cords, and the mucous membrane of the upper part of the trachea.
  • Cardiac branches (two or three) arise in the neck, descend into the thorax, and end in the cardiac plexus (Fig. 11-69).

The vagus nerve thus innervates the heart and great vessels within the thorax; the larynx, trachea, bronchi, and lungs; and much of the alimentary tract from the pharynx to the splenic flexure of the colon. It also supplies glands associated with the alimentary tract, such as the liver and pancreas. The vagus nerve has the most extensive distribution of all the cranial nerves and supplies the aforementioned structures with afferent and efferent fibers. Accessory Nerve The accessory nerve is a motor nerve. It consists of a cranial root (part) and a spinal root (part) (Fig. 11-70). Cranial Root The cranial root emerges from the anterior surface of the medulla oblongata between the olive and the inferior cerebellar peduncle (Fig. 11-70). The nerve runs laterally in the posterior cranial fossa and joins the spinal root. P.768

Figure 11-70 A. Origin and distribution of the accessory nerve. B. Distribution of the hypoglossal nerve.

Spinal Root The spinal root arises from nerve cells in the anterior gray column (horn) of the upper five segments of the cervical part of the spinal cord (Fig. 11-70). The nerve ascends alongside the spinal cord and enters the skull through the foramen magnum. It then turns laterally to join the cranial root. The two roots unite and leave the skull through the jugular foramen. The roots then separate: The cranial root joins the vagus nerves and is distributed in its branches to the muscles of the soft palate and pharynx (via the pharyngeal plexus) and to the muscles of the larynx (except the cricothyroid muscle). The spinal root runs downward and laterally and enters the deep surface of the sternocleidomastoid muscle, which it supplies, and then crosses the posterior triangle of the neck to supply the trapezius muscle (Fig. 11-55). The accessory nerve thus brings about movements of the soft palate, pharynx, and larynx and controls the movements of the sternocleidomastoid and trapezius muscles, two large muscles in the neck. P.769
Clinical Notes Injury to the Spinal Part of the Accessory Nerve The spinal part of the accessory nerve crosses the posterior triangle in a relatively superficial position. It can be injured at operation or from penetrating wounds. The trapezius muscle is paralyzed, the muscle will show wasting, and the shoulder will drop. The patient will experience difficulty in elevating the arm above the head, having abducted it to a right angle by using the deltoid muscle. Clinical examination of this nerve involves asking the patient to rotate the head to one side against resistance, causing the sternocleidomastoid of the opposite side to come into action. Then the patient is asked to shrug the shoulders, causing the trapezius muscles to come into action. Hypoglossal Nerve The hypoglossal nerve is a motor nerve. It emerges on the anterior surface of the medulla oblongata between the pyramid and the olive, crosses the posterior cranial fossa, and leaves the skull through the hypoglossal canal. The nerve then passes downward and forward in the neck and crosses the internal and external carotid arteries to reach the tongue (Fig. 11-70). In the upper part of its course, it is joined by C1 fibers from the cervical plexus. Important Branches of the Hypoglossal Nerve

  • Meningeal branch
  • Descending branch (C1 fibers) passes downward and joins the descending cervical nerve (C2 and 3) to form the ansa cervicalis. Branches from this loop supply the omohyoid, the sternohyoid, and the sternothyroid muscles.
  • Nerve to the thyrohyoid muscle (C1).
  • Muscular branches to all the muscles of the tongue except the palatoglossus (pharyngeal plexus)
  • Nerve to the geniohyoid muscle (C1). The hypoglossal nerve thus innervates the muscles of the tongue (except P.770
    P.771
    the palatoglossus) and therefore controls the shape and movements of the tongue.

Clinical Notes Clinical Testing of the Cranial Nerves Systematic examination of the 12 cranial nerves is an important part of the examination of every neurologic patient. It may reveal a lesion of a cranial nerve nucleus or its central connections, or it may show an interruption of the lower motor neurons. Testing the Integrity of the Olfactory Nerve The olfactory nerve can be tested by applying substances with different odors to each nostril in turn. It should be remembered that food flavors depend on the sense of smell and not on the sense of taste. Fractures of the anterior cranial fossa or cerebral tumors of the frontal lobes may produce lesions of the olfactory nerves, with consequent loss of the sense of smell (anosmia). Testing the Integrity of the Optic Nerve The optic nerve is evaluated by first asking the patient whether any changes in eyesight have been noted. The acuity of vision is then tested by using charts with lines of print of varying size. The retinas and optic discs should then be examined with an ophthalmoscope. When examining the optic disc, it should be remembered that the intracranial subarachnoid space extends forward around the optic nerve to the back of the eyeball. The retinal artery and vein run in the optic nerve and cross the subarachnoid space of the nerve sheath a short distance behind the eyeball. A rise in cerebrospinal fluid pressure in the subarachnoid space will compress the thin walls of the retinal vein as it crosses the space, resulting in congestion of the retinal veins, edema of the retina, and bulging of the optic disc (papilledema). The visual fields should then be tested. The patient is asked to gaze straight ahead at a fixed object with the eye under test, the opposite eye being covered. A small object is then moved in an arc around the periphery of the field of vision, and the patient is asked whether he or she can see the object. It is important not to miss loss or impairment of vision in the central area of the field (central scotoma). Blindness in one half of each visual field is called hemianopia. Lesions of the optic tract and optic radiation produce the same hemianopia for both eyes, that is, homonymous hemianopia. Bitemporal hemianopia is a loss of the lateral halves of the fields of vision of both eyes (i.e., loss of function of the medial half of both retinas). This condition is most commonly produced by a tumor of the pituitary gland exerting pressure on the optic chiasma. Testing the Integrity of the Oculomotor, Trochlear, and Abducent Nerves The oculomotor, trochlear, and abducent nerves innervate the muscles that move the eyeball. The oculomotor nerve supplies all the orbital muscles except the superior oblique and the lateral rectus. It also supplies the levator palpebrae superioris and the smooth muscles concerned with accommodation—namely, the sphincter pupillae and the ciliary muscle. The trochlear nerve supplies the superior oblique muscle, and the abducent nerve supplies the lateral rectus. To examine the ocular muscles, the patient’s head is fixed and he or she is asked to move the eyes in turn to the left, to the right, upward, and downward, as far as possible in each direction. In complete third nerve paralysis the eye cannot be moved upward, downward, or inward. At rest the eye looks laterally (external strabismus) because of the activity of the lateral rectus and downward because of the activity of the superior oblique. The patient sees double (diplopia). Drooping of the upper eyelid (ptosis) occurs because of paralysis of the levator palpebrae superioris. The pupil is widely dilated and nonreactive to light because of the paralysis of the sphincter pupillae and the unopposed action of the dilator pupillae (supplied by the sympathetic). Accommodation of the eye is paralyzed. In fourth nerve paralysis the patient complains of double vision on looking straight downward. This is because the superior oblique is paralyzed and the eye turns medially as the inferior rectus pulls the eye downward. In sixth nerve paralysis the patient cannot turn the eyeball laterally. When looking straight ahead, the lateral rectus is paralyzed, and the unopposed medial rectus pulls the eyeball medially, causing internal strabismus. Testing the Integrity of the Trigeminal Nerve The trigeminal nerve has sensory and motor roots. The sensory root passes to the trigeminal ganglion, from which emerge the ophthalmic (V1), maxillary (V2), and mandibular (V3) divisions. The motor root joins the mandibular division. The sensory function can be tested by using a cotton wisp over each area of the face supplied by the divisions of the trigeminal nerve (Fig. 11-50). The motor function can be tested by asking the patient to clench the teeth. The masseter and the temporalis muscles, which are innervated by the mandibular division of the trigeminal nerve, can be palpated and felt to harden as they contract. Testing the Integrity of the Facial Nerve The facial nerve supplies the muscles of facial expression; supplies the anterior two thirds of the tongue with taste fibers; and is secretomotor to the lacrimal, submandibular, and sublingual glands. The anatomic relationship of this nerve to other structures enables a physician to localize lesions of the nerve accurately. If the sixth and seventh nerves are not functioning, this would suggest a lesion within the pons of the brain. If the eighth and seventh nerves are not functioning, this would suggest a lesion in the internal acoustic meatus. If the patient is excessively sensitive to sound in one ear, the lesion probably involves the nerve to the stapedius. Loss of taste over the anterior two thirds of the tongue implies that the seventh nerve is damaged proximal to the point where it gives off the chorda tympani. To test the facial nerve, the patient is asked to show the teeth by separating the lips with the teeth clenched, and then to close the eyes. Taste on each half of the anterior two thirds of the tongue can be tested with sugar, salt, vinegar, and quinine for the sweet, salt, sour, and bitter sensations, respectively. It should be remembered that the part of the facial nerve nucleus that controls the muscles of the upper part of the face receives corticobulbar fibers from both cerebral cortices. Therefore, in patients with an upper motor neuron lesion, only the muscles of the lower part of the face will be paralyzed. However, in patients with a lower motor neuron lesion, all the muscles on the affected side of the face will be paralyzed. The lower eyelid will droop, and the angle of the mouth will sag. Tears will flow over the lower eyelid, and saliva will dribble from the corner of the mouth. The patient will be unable to close the eye and cannot expose the teeth fully on the affected side. Testing the Integrity of the Vestibulocochlear Nerve The vestibulocochlear nerve innervates the utricle and saccule, which are sensitive to static changes in equilibrium; the semicircular canals, which are sensitive to changes in dynamic equilibrium; and the cochlea, which is sensitive to sound. Disturbances of vestibular function include dizziness (vertigo) and nystagmus. The latter is an uncontrollable pendular movement of the eyes. Disturbances of cochlear function reveal themselves as deafness and ringing in the ears (tinnitus). The patient’s ability to hear a voice or a tuning fork should be tested, with each ear tested separately. Testing the Integrity of the Glossopharyngeal Nerve The glossopharyngeal nerve supplies the stylopharyngeus muscle and sends secretomotor fibers to the parotid gland. Sensory fibers innervate the posterior one third of the tongue. The integrity of this nerve may be evaluated by testing the patient’s general sensation and that of taste on the posterior third of the tongue. Testing the Integrity of the Vagus Nerve The vagus nerve innervates many important organs, but the examination of this nerve depends on testing the function of the branches to the pharynx, soft palate, and larynx. The pharyngeal reflex may be tested by touching the lateral wall of the pharynx with a spatula. This should immediately cause the patient to gag—that is, the pharyngeal muscles will contract. The innervation of the soft palate can be tested by asking the patient to say “ah.” Normally, the soft palate rises and the uvula moves backward in the midline. All the muscles of the larynx are supplied by the recurrent laryngeal branch of the vagus, except the cricothyroid muscle, which is supplied by the external laryngeal branch of the superior laryngeal branch of the vagus. Hoarseness or absence of the voice may occur. Laryngoscopic examination may reveal abductor paralysis (see page 807). Testing the Integrity of the Accessory Nerve The accessory nerve supplies the sternocleidomastoid and the trapezius muscles by means of its spinal part. The patient should be asked to rotate the head to one side against resistance, causing the sternocleidomastoid of the opposite side to come into action. Then the patient should be asked to shrug the shoulders, causing the trapezius muscles to come into action. Testing the Integrity of the Hypoglossal Nerve The hypoglossal nerve supplies the muscles of the tongue. The patient is asked to put out the tongue, and if a lesion of the nerve is present, it will be noted that the tongue deviates toward the paralyzed side (Fig. 11-78). This can be explained as follows. One of the genioglossus muscles, which pull the tongue forward, is paralyzed on the affected side. The other, normal genioglossus muscle pulls the unaffected side of the tongue forward, leaving the paralyzed side of the tongue stationary. The result is the tip of the tongue’s deviation toward the paralyzed side. In patients with long-standing paralysis, the muscles on the affected side are wasted, and the tongue is wrinkled on that side.

Table 11-7 Summary of the Branches of the Cervical Plexus and Their Distribution
Branches Distribution
Cutaneous
    Lesser occipital Skin of scalp behind ear
    Greater auricular Skin over parotid salivary gland, auricle, and angle of jaw
    Transverse cutaneous Skin over side and front of neck
    Supraclavicular Skin over upper part of chest and shoulder
Muscular
    Segmental Prevertebral muscles, levator scapulae
    Ansa cervicalis (C1, 2, 3) Omohyoid, sternohyoid, sternothyroid
    C1 fibers via hypoglossal nerve Thyrohyoid, geniohyoid
    Phrenic nerve (C3, 4, 5) Diaphragm (most important muscle of respiration)
Sensory
    Phrenic nerve (C3, 4, 5) Pericardium, mediastinal parietal pleura, and pleura and peritoneum covering central diaphragm

Main Nerves of the Neck Cervical Plexus The cervical plexus is formed by the anterior rami of the first four cervical nerves. The rami are joined by connecting branches, which form loops that lie in front of the origins of the levator scapulae and the scalenus medius muscles (Fig. 11-57). The plexus is covered in front by the prevertebral layer of deep cervical fascia and is related to the internal jugular vein within the carotid sheath. The cervical plexus supplies the skin and the muscles of the head, the neck, and the shoulders. Branches

  • Cutaneous branches The lesser occipital nerve (C2), which supplies the back of the scalp and the auricle The greater auricular nerve (C2 and3), which supplies the skin over the angle of the mandible The transverse cervical nerve (C2 and 3), which supplies the skin over the front of the neck The supraclavicular nerves (C3 and 4). The medial, and intermediate, and lateral branches supply the skin over the shoulder region. These nerves are important clinically, because pain may be referred along them from the phrenic nerve (gallbladder disease).
  • Muscular branches to the neck muscles. Prevertebral muscles, sternocleidomastoid (proprioceptive, C2 and 3), levator scapulae (C3 and 4), and trapezius (proprioceptive, C3 and 4). A branch from C1 joins the hypoglossal nerve. Some of these C1 fibers later leave the hypoglossal as the descending branch, which unites with the descending cervical nerve (C2 and 3), to form the ansa cervicalis (Fig. 11-60). The first, second, and third cervical nerve fibers within the ansa cervicalis supply the omohyoid, sternohyoid, and sternothyroid muscles. Other C1 fibers within the hypoglossal nerve leave it as the nerve to the thyrohyoid and geniohyoid.
  • Muscular branch to the diaphragm. Phrenic nerve

Phrenic Nerve The phrenic nerve arises in the neck from the third, fourth, and fifth cervical nerves of the cervical plexus. It runs vertically downward across the front of the scalenus anterior muscle (Fig. 11-57) and enters the thorax by passing in front of the subclavian artery. Its further course in the thorax is described on page 127. The phrenic nerve is the only motor nerve supply to the diaphragm. It also sends sensory branches to the pericardium, the mediastinal parietal pleura, and the pleura and peritoneum covering the upper and lower surfaces of the central part of the diaphragm. Table 11-7 summarizes the branches of the cervical plexus and their distribution. Clinical Notes Phrenic Nerve Injury and Paralysis of the Diaphragm The phrenic nerve, which arises from the anterior rami of the third, fourth, and fifth cervical nerves, is of considerable clinical importance because it is the sole nerve supply to the muscle of the diaphragm. Each phrenic nerve supplies the corresponding half of the diaphragm. The phrenic nerve can be injured by penetrating wounds in the neck. If that occurs, the paralyzed half of the diaphragm relaxes and is pushed up into the thorax by the positive abdominal pressure. Consequently, the lower lobe of the lung on that side may collapse. About one third of persons have an accessory phrenic nerve. The root from the fifth cervical nerve may be incorporated in the nerve to the subclavius and may join the main phrenic nerve trunk in the thorax. Brachial Plexus The brachial plexus is formed in the posterior triangle of the neck by the union of the anterior rami of the fifth, sixth, seventh, and eighth cervical and the first thoracic spinal nerves (Fig. 11-71). This plexus is divided into roots, trunks, divisions, and cords. The roots of C5 and 6 unite to form the upper trunk, the root of C7 continues as the middle trunk, and the roots of C8 and T1 unite to form the lower trunk. Each trunk then divides into anterior and posterior divisions. The anterior divisions of the upper and middle trunks unite to form the lateral cord, the anterior division of the lower trunk continues as the medial cord, and the posterior divisions of all three trunks join to form the posterior cord. P.772

Figure 11-71 Brachial plexus and its branches.

The roots of the brachial plexus enter the base of the neck between the scalenus anterior and the scalenus medius muscles (Fig. 11-57). The trunks and divisions cross the posterior triangle of the neck, and the cords become arranged around the axillary artery in the axilla (see Fig. 9-20). Here, the brachial plexus and the axillary artery and vein are enclosed in the axillary sheath. Branches The branches of the brachial plexus and their distribution are summarized in Table 9-4. Clinical Notes Injury to the Brachial Plexus The roots and trunks of the brachial plexus occupy the anteroinferior angle of the posterior triangle of the neck. Incomplete lesions can result from stab or bullet wounds, traction, or pressure injuries. The clinical findings in the Erb-Duchenne and the Klumpke’s lesions are fully described on pages 536 and 537. Brachial Plexus Nerve Block It will be remembered that the axillary sheath, formed from the prevertebral layer of deep cervical fascia, encloses the brachial plexus and the axillary artery. A brachial plexus nerve block can easily be obtained by closing the distal part of the sheath in the axilla with finger pressure, inserting a syringe needle into the proximal part of the sheath, and then injecting a local anesthetic. The anesthetic solution is massaged along the sheath, producing a nerve block. The syringe needle may be inserted into the axillary sheath in the lower part of the posterior triangle of the neck or in the axilla. Compression of the Brachial Plexus and the Subclavian Artery At the root of the neck, the brachial plexus and the subclavian artery enter the posterior triangle through a narrow muscular–bony triangle. The boundaries of the narrow triangle are formed in front by the scalenus anterior, behind by the scalenus medius, and below by the first rib. In the presence of a cervical rib (see page 50), the first thoracic nerve and the subclavian artery are raised and angulated as they pass over the rib. Partial or complete occlusion of the artery causes ischemic muscle pain in the arm, which is worsened by exercise. Rarely, pressure on the first thoracic nerve causes symptoms of pain in the forearm and hand and wasting of the small muscles of the hand. P.773
The Autonomic Nervous System in the Head and Neck Sympathetic Part Cervical Part of the Sympathetic Trunk The cervical part of the sympathetic trunk extends upward to the base of the skull and below to the neck of the first rib, where it becomes continuous with the thoracic part of the sympathetic trunk. It lies directly behind the internal and common carotid arteries (i.e., medial to the vagus) and is embedded in deep fascia between the carotid sheath and the prevertebral layer of deep fascia (Fig. 11-49). The sympathetic trunk possesses three ganglia: the superior, middle, and inferior cervical ganglia. Superior Cervical Ganglion The superior cervical ganglion lies immediately below the skull (Fig. 11-60). Branches

  • The internal carotid nerve, consisting of postganglionic fibers, accompanies the internal carotid artery into the carotid canal in the temporal bone. It divides into branches around the artery to form the internal carotid plexus.
  • Gray rami communicantes to the upper four anterior rami of the cervical nerves
  • Arterial branches to the common and external carotid arteries. These branches form a plexus around the arteries and are distributed along the branches of the external carotid artery.
  • Cranial nerve branches, which join the 9th, 10th, and 12th cranial nerves
  • Pharyngeal branches, which unite with the pharyngeal branches of the glossopharyngeal and vagus nerves to form the pharyngeal plexus
  • The superior cardiac branch, which descends in the neck and ends in the cardiac plexus in the thorax (see page 116)

Middle Cervical Ganglion The middle cervical ganglion lies at the level of the cricoid cartilage (Fig. 11-57). Branches

  • Gray rami communicantes to the anterior rami of the fifth and sixth cervical nerves
  • Thyroid branches, which pass along the inferior thyroid artery to the thyroid gland
  • The middle cardiac branch, which descends in the neck and ends in the cardiac plexus in the thorax (see page 116)

Inferior Cervical Ganglion The inferior cervical ganglion in most people is fused with the first thoracic ganglion to form the stellate ganglion. It lies in the interval between the transverse process of the seventh cervical vertebra and the neck of the first rib, behind the vertebral artery (Fig. 11-57). Branches

  • Gray rami communicantes to the anterior rami of the seventh and eighth cervical nerves
  • Arterial branches to the subclavian and vertebral arteries
  • The inferior cardiac branch, which descends to join the cardiac plexus in the thorax (see page 116)

The part of the sympathetic trunk connecting the middle cervical ganglion to the inferior or stellate ganglion is represented by two or more nerve bundles. The most anterior bundle crosses in front of the first part of the subclavian artery and then turns upward behind it. This anterior bundle is referred to as the ansa subclavia (Figs. 11-57 and 11-60). Clinical Notes Sympathectomy for Arterial Insufficiency of the Upper Limb The sympathetic innervation of the upper limb is as follows: The preganglionic fibers leave the spinal cord in the second to the eighth thoracic nerves. On reaching the sympathetic trunk via the white rami, they ascend within the trunk and are relayed in the second thoracic, stellate, and middle cervical ganglia. Postganglionic fibers then join the roots of the brachial plexus as gray rami. Sympathectomy of the upper limb is a relatively common procedure for the treatment of arterial insufficiency. From this information, it is clear that the stellate and the second thoracic ganglia should be removed to block the sympathetic pathway to the arm completely. Removal of the stellate ganglion also removes the sympathetic nerve supply to the head and neck on that side. This produces not only vasodilatation of the skin vessels, but also anhidrosis, nasal congestion, and Horner’s syndrome. For this reason the stellate ganglion is usually left intact in sympathectomies of the upper limb. Horner’s Syndrome Horner’s syndrome includes constriction of the pupil, ptosis (drooping of the upper eyelid), and enophthalmos (depression of the eyeball into the orbital cavity). It is caused by an interruption of the sympathetic nerve supply to the orbit. Pathologic causes include lesions of the brainstem or cervical part of the spinal cord; traumatic injury to the cervical part of the sympathetic trunk; traction of the stellate ganglion caused by a cervical rib; and involvement of the ganglion in cancerous growth, which may interrupt the peripheral part of the sympathetic pathway to the orbit. Stellate Ganglion Block A stellate ganglion block is performed by first palpating the large anterior tubercle (carotid tubercle) of the transverse process of the sixth cervical vertebra, which lies about a fingerbreadth lateral to the cricoid cartilage. The carotid sheath and the sternocleidomastoid muscle are pushed laterally and the needle of the anesthetic syringe is inserted through the skin over the tubercle. The local anesthetic is then injected beneath the prevertebral layer of deep cervical fascia. This procedure effectively blocks the ganglion and its rami communicantes. P.774
Parasympathetic Part The cranial portion of the craniosacral outflow of the parasympathetic part of the autonomic nervous system is located in the nuclei of the oculomotor (3rd), facial (7th), glossopharyngeal (9th), and vagus (10th) cranial nerves. The parasympathetic nucleus of the oculomotor nerve is called the Edinger-Westphal nucleus; those of the facial nerve the lacrimatory and the superior salivary nuclei; that of the glossopharyngeal nerve the inferior salivary nucleus; and that of the vagus nerve the dorsal nucleus of the vagus. The axons of these connector nerve cells are myelinated preganglionic fibers that emerge from the brain within the cranial nerves. These preganglionic fibers synapse in peripheral ganglia located close to the viscera they innervate. The cranial parasympathetic ganglia are the ciliary, the pterygopalatine, the submandibular, and the otic. In certain locations, the ganglion cells are placed in nerve plexuses, such as the cardiac plexus, the pulmonary plexus, the myenteric plexus (Auerbach’s plexus), and the mucosal plexus (Meissner’s plexus). The last two plexuses are found in the gastrointestinal tract. The postganglionic fibers are nonmyelinated, and they are short in length. The Digestive System in the Head and Neck The Mouth The Lips The lips are two fleshy folds that surround the oral orifice (Fig. 11-72). They are covered on the outside by skin and are lined on the inside by mucous membrane. The substance of the lips is made up by the orbicularis oris muscle and the muscles that radiate from the lips into the face (Fig. 11-73). Also included are the labial blood vessels and nerves, connective tissue, and many small salivary glands. The philtrum is the shallow vertical groove seen in the midline on the outer surface of the upper lip. Median folds of mucous membrane—the labial frenulae—connect the inner surface of the lips to the gums. The Mouth Cavity The mouth extends from the lips to the pharynx. The entrance into the pharynx, the oropharyngeal isthmus, is formed on each side by the palatoglossal fold (Fig. 11-72). The mouth is divided into the vestibule and the mouth cavity proper. Vestibule The vestibule lies between the lips and the cheeks externally and the gums and the teeth internally. This slitlike space communicates with the exterior through the oral fissure between the lips. When the jaws are closed, it communicates with the mouth proper behind the third molar tooth on each side. The vestibule is limited above and below by the reflection of the mucous membrane from the lips and cheeks to the gums. The lateral wall of the vestibule is formed by the cheek, which is made up by the buccinator muscle and is lined with mucous membrane. The tone of the buccinator muscle and that of the muscles of the lips keeps the walls of the vestibule in contact with one another. The duct of the parotid salivary gland opens on a small papilla into the vestibule opposite the upper second molar tooth (Fig. 11-72). Mouth Proper The mouth proper has a roof and a floor. Roof of Mouth The roof of the mouth is formed by the hard palate in front and the soft palate behind (Fig. 11-72). Floor of Mouth The floor is formed largely by the anterior two thirds of the tongue and by the reflection of the mucous membrane from the sides of the tongue to the gum of the mandible. A fold of mucous membrane called the frenulum of the tongue connects the undersurface of the tongue in the midline to the floor of the mouth (Fig. 11-72). Lateral to the frenulum, the mucous membrane forms a fringed fold, the plica fimbriata (Fig. 11-72). The submandibular duct of the submandibular gland opens onto the floor of the mouth on the summit of a small papilla on either side of the frenulum of the tongue (Fig. 11-72). The sublingual gland projects up into the mouth, producing a low fold of mucous membrane, the sublingual fold. Numerous ducts of the gland open on the summit of the fold. P.775

Figure 11-72 A. Cavity of the mouth. Cheek on the left side of the face has been cut away to show the buccinator muscle and the parotid duct. B. Undersurface of the tongue.

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Figure 11-73 Arrangement of the facial muscles around the lips; the sensory nerve supply of the lips is shown.

Mucous Membrane of the Mouth In the vestibule the mucous membrane is tethered to the buccinator muscle by elastic fibers in the submucosa that prevent redundant folds of mucous membrane from being bitten between the teeth when the jaws are closed. The mucous membrane of the gingiva, or gum, is strongly attached to the alveolar periosteum. Sensory Innervation of the Mouth

  • Roof: The greater palatine and nasopalatine nerves (Fig. 11-74) from the maxillary division of the trigeminal nerve
  • Floor: The lingual nerve (common sensation), a branch of the mandibular division of the trigeminal nerve. The taste fibers travel in the chorda tympani nerve, a branch of the facial nerve.
  • Cheek: The buccal nerve, a branch of the mandibular division of the trigeminal nerve (the buccinator muscle is innervated by the buccal branch of the facial nerve)

Clinical Notes Clinical Significance of the Examination of the Mouth The mouth is one of the important areas of the body that the medical professional is called on to examine. Needless to say, the physician must be able to recognize all the structures visible in the mouth and be familiar with the normal variations in the color of the mucous membrane covering underlying structures. The sensory nerve supply and lymph drainage of the mouth cavity should be known. The close relation of the lingual nerve to the lower third molar tooth should be remembered. The close relation of the submandibular duct to the floor of the mouth may enable one to palpate a calculus in cases of periodic swelling of the submandibular salivary gland. Embryologic Notes Development of the Mouth The cavity of the mouth is formed from two sources: a depression from the exterior, called the stomodeum, which is lined with ectoderm, and a part immediately posterior to this, derived from the cephalic end of the foregut and lined with entoderm. These two parts at first are separated by the buccopharyngeal membrane, but this breaks down and disappears during the third week of development (Fig. 11-75). If this membrane were to persist into adult life, it would occupy an imaginary plane extending obliquely from the region of the body of the sphenoid, through the soft palate, and down to the inner surface of the mandible inferior to the incisor teeth. This means that the structures that are situated in the mouth anterior to this plane are derived from ectoderm. Thus, the epithelium of the hard palate, sides of the mouth, lips, and enamel of the teeth are ectodermal structures. The secretory epithelium and cells lining the ducts of the parotid salivary gland also are derived from ectoderm. On the other hand, the epithelium of the tongue, the floor of the mouth, the palatoglossal and palatopharyngeal folds, and most of the soft palate are entodermal in origin. The secretory and duct epithelia of the sublingual and submandibular salivary glands also are believed to be of entodermal origin. P.777

Figure 11-74 A. Sensory nerve supply to the mucous membrane of the tongue. B. Sensory nerve supply to the mucous membrane of the hard and soft palate; taste fibers run with branches of the maxillary nerve (V2) and join the greater petrosal branch of the facial nerve.
Figure 11-75 A. Sagittal section of the embryo showing the position of the buccopharyngeal membrane. B. The face of the developing embryo showing the buccopharyngeal membrane breaking down.

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The Teeth Deciduous Teeth There are 20 deciduous teeth: four incisors, two canines, and four molars in each jaw. They begin to erupt about 6 months after birth and have all erupted by the end of 2 years. The teeth of the lower jaw usually appear before those of the upper jaw. Permanent Teeth There are 32 permanent teeth: four incisors, two canines, four premolars, and six molars in each jaw (Fig. 11-76). They begin to erupt at 6 years of age. The last tooth to erupt is the third molar, which may happen between the ages of 17 and 30. The teeth of the lower jaw appear before those of the upper jaw. The Tongue The tongue is a mass of striated muscle covered with mucous membrane (Fig. 11-77). The muscles attach the tongue to the styloid process and the soft palate above and to the mandible and the hyoid bone below. The tongue is divided into right and left halves by a median fibrous septum. Mucous Membrane of the Tongue The mucous membrane of the upper surface of the tongue can be divided into anterior and posterior parts by a V-shaped sulcus, the sulcus terminalis (Fig. 11-77). The apex of the sulcus projects backward and is marked by a small pit, the foramen cecum. The sulcus serves to divide the tongue into the anterior two thirds, or oral part, and the posterior third, or pharyngeal part. The foramen cecum is an embryologic remnant P.779
and marks the site of the upper end of the thyroglossal duct (see page 819).

Figure 11-76 Sagittal section through the lower jaw and gum showing an erupted temporary incisor tooth and a developing permanent tooth.
Figure 11-77 Dorsal surface of the tongue showing the valleculae, the epiglottis, and the entrance into the piriform fossa on each side (arrows).

Three types of papillae are present on the upper surface of the anterior two thirds of the tongue: the filiform papillae, the fungiform papillae, and the vallate papillae. The mucous membrane covering the posterior third of the tongue is devoid of papillae but has an irregular surface (Fig. 11-77), caused by the presence of underlying lymph nodules, the lingual tonsil. The mucous membrane on the inferior surface of the tongue is reflected from the tongue to the floor of the mouth. In the midline anteriorly, the undersurface of the tongue is connected to the floor of the mouth by a fold of mucous membrane, the frenulum of the tongue. On the lateral side of the frenulum, the deep lingual vein can be seen through the mucous membrane. Lateral to the lingual vein, the mucous membrane forms a fringed fold called the plica fimbriata (Fig. 11-72). Muscles of the Tongue The muscles of the tongue are divided into two types: intrinsic and extrinsic. Intrinsic Muscles These muscles are confined to the tongue and are not attached to bone. They consist of longitudinal, transverse, and vertical fibers.

  • Nerve supply: Hypoglossal nerve
  • Action: Alter the shape of the tongue

Extrinsic Muscles These muscles are attached to bones and the soft palate. They are the genioglossus, the hyoglossus, the styloglossus, and the palatoglossus.

  • Nerve supply: Hypoglossal nerve

The origin, insertion, nerve supply, and action of the tongue muscles are summarized in Table 11-8. Blood Supply The lingual artery, the tonsillar branch of the facial artery, and the ascending pharyngeal artery supply the tongue. The veins drain into the internal jugular vein. Lymph Drainage

  • Tip: Submental lymph nodes
  • Sides of the anterior two thirds: Submandibular and deep cervical lymph nodes
  • Posterior third: Deep cervical lymph nodes

Sensory Innervation

  • Anterior two thirds: Lingual nerve branch of mandibular division of trigeminal nerve (general sensation) and chorda tympani branch of the facial nerve (taste)
  • Posterior third: Glossopharyngeal nerve (general sensation and taste)

Movements of the Tongue

  • Protrusion: The genioglossus muscles on both sides acting together (Fig. 11-78)
  • Retraction: Styloglossus and hyoglossus muscles on both sides acting together
  • Depression: Hyoglossus muscles on both sides acting together
  • Retraction and elevation of the posterior third: Styloglossus and palatoglossus muscles on both sides acting together
  • Shape changes: Intrinsic muscles

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Table 11-8 Muscles of Tongue
Muscle Origin Insertion Nerve Supply Action
Intrinsic Muscles
Longitudinal Median septum and submucosa Mucous membrane Hypoglossal nerve Alters shape of tongue
Transverse
Vertical
Extrinsic Muscles
Genioglossus Superior genial spine of mandible Blends with other muscles of tongue Hypoglossal nerve Protrudes apex of tongue through mouth
Hyoglossus Body and greater cornu of hyoid bone Blends with other muscles of tongue Hypoglossal nerve Depresses tongue
Styloglossus Styloid process of temporal bone Blends with other muscles of tongue Hypoglossal nerve Draws tongue upward and backward
Palatoglossus Palatine aponeurosis Side of tongue Pharyngeal plexus Pulls roots of tongue upward and backward, narrows oropharyngeal isthmus
Figure 11-78 Diagrammatic representation of the action of the right and left genioglossus muscles of the tongue. A. The right and left muscles contract equally together and as a result (B) the tip of the tongue is protruded in the midline. C. The right hypoglossal nerve (which innervates the genioglossus muscle and the intrinsic tongue muscles on the same side) is cut and as a result the right side of the tongue is atrophied and wrinkled. D. When the patient is asked to protrude the tongue, the tip points to the side of the nerve lesion. E. The origin and insertion and direction of pull of the genioglossus muscle.

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Embryologic NOTES Development of the Tongue At about the fourth week, a median swelling called the tuberculum impar appears in the entodermal ventral wall or floor of the pharynx (Fig. 11-79). A little later, another swelling, called the lateral lingual swelling (derived from the anterior end of each first pharyngeal arch), appears on each side of the tuberculum impar. The lateral lingual swellings now enlarge, grow medially, and fuse with each other and the tuberculum impar. The lingual swellings thus form the anterior two thirds of the body of the tongue, and since they are derived from the first pharyngeal arches, the mucous membrane on each side will be innervated by the lingual nerve, a branch of the mandibular division of the fifth cranial nerve (common sensation). The chorda tympani from the seventh cranial nerve (taste) also supplies this area. Meanwhile, a second median swelling, called the copula, appears in the floor of the pharynx behind the tuberculum impar. The copula extends forward on each side of the tuberculum impar and becomes V shaped. At about this time, the anterior ends of the second, third, and fourth pharyngeal arches are entering this region. The anterior ends of the third arch on each side overgrow the other arches and extend into the copula, fusing in the midline. The copula now disappears. Thus, the mucous membrane of the posterior third of the tongue is formed from the third pharyngeal arches and is innervated by the ninth cranial nerve (common sensation and taste). The anterior two thirds of the tongue is separated from the posterior third by a groove, the sulcus terminalis, which represents the interval between the lingual swellings of the first pharyngeal arches and the anterior ends of the third pharyngeal arches. Around the edge of the anterior two thirds of the tongue, the entodermal cells proliferate and grow inferiorly into the underlying mesenchyme. Later, these cells degenerate so that this part of the tongue becomes free. Some of the entodermal cells remain in the midline and help form the frenulum of the tongue. Remember that the circumvallate papillae are situated on the mucous membrane just anterior to the sulcus terminalis, and that their taste buds are innervated by the ninth cranial nerve. It is presumed that during development the mucous membrane of the posterior third of the tongue becomes pulled anteriorly slightly, so that fibers of the ninth cranial nerve cross the succus terminalis to supply these taste buds (Fig. 11-79). The muscles of the tongue are derived from the occipital myotomes, which at first are closely related to the developing hindbrain and later migrate inferiorly and anteriorly around the pharynx and enter the tongue. The migrating myotomes carry with them their innervation, the 12th cranial nerve, and this explains the long curving course taken by the 12th cranial nerve as it passes downward and forward in the carotid triangle of the neck (see page 769). Clinical Notes Laceration of the Tongue A wound of the tongue is often caused by the patient’s teeth following a blow on the chin when the tongue is partly protruded from the mouth. It can also occur when a patient accidentally bites the tongue while eating, during recovery from an anesthetic, or during an epileptic attack. Bleeding is halted by grasping the tongue between the finger and thumb posterior to the laceration, thus occluding the branches of the lingual artery. The Palate The palate forms the roof of the mouth and the floor of the nasal cavity. It is divided into two parts: the hard palate in front and the soft palate behind. Hard Palate The hard palate is formed by the palatine processes of the maxillae and the horizontal plates of the palatine bones (Fig. 11-80). It is continuous behind with the soft palate. Soft Palate The soft palate is a mobile fold attached to the posterior border of the hard palate (Fig. 11-81). Its free posterior border presents in the midline a conical projection called the uvula. The soft palate is continuous at the sides with the lateral wall of the pharynx. The soft palate is composed of mucous membrane, palatine aponeurosis, and muscles. Mucous Membrane The mucous membrane covers the upper and lower surfaces of the soft palate. Palatine Aponeurosis The palatine aponeurosis is a fibrous sheet attached to the posterior border of the hard palate. It is the expanded tendon of the tensor veli palatini muscle. Muscles of the Soft Palate The muscles of the soft palate are the tensor veli palatini, the levator veli palatini, the palatoglossus, the palatopharyngeus, and the musculus uvulae (Fig. 11-81). The muscle fibers of the tensor veli palatini converge as they descend from their origin to form a narrow tendon, which turns medially around the pterygoid hamulus. The tendon, together with the tendon of the opposite side, expands to form the palatine aponeurosis. When the muscles of the two sides contract, the soft palate is tightened so that the soft palate may be moved upward or downward as a tense sheet. The muscles of the soft palate, their origins, insertions, nerve supply, and actions are summarized in Table 11-9. P.782

Figure 11-79 The floor of the pharynx showing the stages in the development of the tongue.

Nerve Supply of the Palate The greater and lesser palatine nerves from the maxillary division of the trigeminal nerve enter the palate through the greater and lesser palatine foramina (Fig. 11-74). The nasopalatine nerve, also a branch of the maxillary nerve, enters the front of the hard palate through the incisive foramen. The glossopharyngeal nerve also supplies the soft palate. Blood Supply of the Palate The greater palatine branch of the maxillary artery, the ascending palatine branch of the facial artery, and the ascending pharyngeal artery Lymph Drainage of the Palate Deep Cervical Lymph Nodes Palatoglossal Arch The palatoglossal arch is a fold of mucous membrane containing the palatoglossus muscle, which extends from the soft palate to the side of the tongue (Figs. 11-72 and 11-81). The palatoglossal arch marks where the mouth becomes the pharynx. Palatopharyngeal Arch The palatopharyngeal arch is a fold of mucous membrane behind the palatoglossal arch (Figs. 11-72 and 11-81) that runs downward and laterally to join the pharyngeal wall. The muscle contained within the fold is the palatopharyngeus muscle. The palatine tonsils, which are masses of lymphoid tissue, are located between the palatoglossal and palatopharyngeal arches (Fig. 11-81). P.783

Figure 11-80 A. Three constrictor muscles of the pharynx. The superior and recurrent laryngeal nerves are also shown. B. Hard palate.

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Figure 11-81 A. Junction of the nose with the nasal part of the pharynx and the mouth with the oral part of the pharynx. Note the position of the tonsil and the opening of the auditory tube. B. Muscles of the soft palate and the upper part of the pharynx. C. Muscles of the soft palate seen from behind. D. Horizontal section through the mouth and the oral part of the pharynx showing the relations of the tonsil.

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Table 11-9 Muscles of the Soft Palate
Muscle Origin Insertion Nerve Supply Action
Tensor veli palatini Spine of sphenoid, auditory tube With muscle of other side, forms palatine aponeurosis Nerve to medial pterygoid from mandibular nerve Tenses soft palate
Levator veli palatini Petrous part of temporal bone, auditory tube Palatine aponeurosis Pharyngeal plexus Raises soft palate
Palatoglossus Palatine aponeurosis Side of tongue Pharyngeal plexus Pulls root of tongue upward and backward, narrows oropharyngeal isthmus
Palatopharyngeus Palatine aponeurosis Posterior border of thyroid cartilage Pharyngeal plexus Elevates wall of pharynx, pulls palatopharyngeal folds medially
Musculus uvulae Posterior border of hard palate Mucous membrane of uvula Pharyngeal plexus Elevates uvula

Movements of the Soft Palate The pharyngeal isthmus (the communicating channel between the nasal and oral parts of the pharynx) is closed by raising the soft palate. Closure occurs during the production of explosive consonants in speech. The soft palate is raised by the contraction of the levator veli palatini on each side. At the same time, the upper fibers of the superior constrictor muscle contract and pull the posterior pharyngeal wall forward. The palatopharyngeus muscles on both sides also contract so that the palatopharyngeal arches are pulled medially, like side curtains. By this means the nasal part of the pharynx is closed off from the oral part. Clinical Notes Angioedema of the Uvula (Quincke’s Uvula) The uvula has a core of voluntary muscle, the musculus uvulae, that is attached to the posterior border of the hard palate. Surrounding the muscle is the loose connective tissue of the submucosa that is responsible for the great swelling of this structure secondary to angioedema. Embryologic Notes Development of the Palate In early fetal life, the nasal and mouth cavities are in communication, but later they become separated by the development of the palate (Fig. 11-82). The primary palate, which carries the four incisor teeth, is formed by the medial nasal process. Posterior to the primary palate, the maxillary process on each side sends medially a horizontal plate called the palatal process; these plates fuse to form the secondary palate and also unite with the primary palate and the developing nasal septum. The fusion takes place from the anterior to the posterior region. The primary and secondary palates later will form the hard palate. Two folds grow posteriorly from the posterior edge of the palatal processes to create the soft palate, so that the uvula is the last structure to be formed (Fig. 11-82). The union of the two folds of the soft palate occurs during the eighth week. The two parts of the uvula fuse in the midline during the 11th week. The interval between the primary palate and secondary palate is represented in the midline by the incisive foramen. Cleft Palate Cleft palate is commonly associated with cleft upper lip. All degrees of cleft palate occur and are caused by failure of the palatal processes of the maxilla to fuse with each other in the midline; in severe cases, these processes also fail to fuse with the primary palate (premaxilla) (Figs. 11-83 and 11-84). The first degree of severity is cleft uvula, and the second degree is ununited palatal processes. The third degree is ununited palatal processes and a cleft on one side of the primary palate. This type is usually associated with unilateral cleft lip. The fourth degree of severity, which is rare, consists of ununited palatal processes and a cleft on both sides of the primary palate. This type is usually associated with bilateral cleft lip. A rare form may occur in which a bilateral cleft lip and failure of the primary palate to fuse with the palatal processes of the maxilla on each side are present. A baby born with a severe cleft palate presents a difficult feeding problem, since he or she is unable to suck efficiently. Such a baby often receives in the mouth some milk, which then is regurgitated through the nose or aspirated into the lungs, leading to respiratory infection. For this reason, careful artificial feeding is required until the baby is strong enough to undergo surgery. Plastic surgery is recommended usually between 1 and 2 years of age, before improper speech habits have been acquired. P.786

Figure 11-82 A. The formation of the palate and the nasal septum (coronal section). B. The different stages in the formation of the palate.

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Figure 11-83 Different forms of cleft palate: cleft uvula (A), cleft soft and hard palate (B), total unilateral cleft palate and cleft lip (C), total bilateral cleft palate and cleft lip (D), and bilateral cleft lip and jaw (E).

The Salivary Glands Parotid Gland The parotid gland is the largest salivary gland and is composed mostly of serous acini. It lies in a deep hollow below the external auditory meatus, behind the ramus of the mandible (Fig. 11-85), and in front of the sternocleidomastoid muscle. The facial nerve divides the gland into superficial and deep lobes. The parotid duct emerges from the anterior border of the gland and passes forward over the lateral surface of the masseter. It enters the vestibule of the mouth upon a small papilla opposite the upper second molar tooth (Fig. 11-72).

Figure 11-84 Cleft hard and soft palate. (Courtesy of R. Chase.)

Nerve Supply Parasympathetic secretomotor supply arises from the glossopharyngeal nerve. The nerves reach the gland via the tympanic branch, the lesser petrosal nerve, the otic ganglion, and the auriculotemporal nerve. Clinical Notes Parotid Duct Injury The parotid duct, which is a comparatively superficial structure on the face, may be damaged in injuries to the face or may be inadvertently cut during surgical operations on the face. The duct is about 2 in. (5 cm) long and passes forward across the masseter about a fingerbreadth below the zygomatic arch. It then pierces the buccinator muscle to enter the mouth opposite the upper second molar tooth. Clinical Notes Parotid Salivary Gland and Lesions of the Facial Nerve The parotid salivary gland consists essentially of superficial and deep parts, and the important facial nerve lies in the interval between these parts. A benign parotid neoplasm rarely, if ever, causes facial palsy. A malignant tumor of the parotid is usually highly invasive and quickly involves the facial nerve, causing unilateral facial paralysis. Parotid Gland Infections The parotid gland may become acutely inflamed as a result of retrograde bacterial infection from the mouth via the parotid duct. The gland may also become infected via the bloodstream, as in mumps. In both cases the gland is swollen; it is painful because the fascial capsule derived from the investing layer of deep cervical fascia is strong and limits the swelling of the gland. The swollen glenoid process, which extends medially behind the temporomandibular joint, is responsible for the pain experienced in acute parotitis when eating. Frey’s Syndrome Frey’s syndrome is an interesting complication that sometimes develops after penetrating wounds of the parotid gland. When the patient eats, beads of perspiration appear on the skin covering the parotid. This condition is caused by damage to the auriculotemporal and great auricular nerves. During the process of healing, the parasympathetic secretomotor fibers in the auriculotemporal nerve grow out and join the distal end of the great auricular nerve. Eventually, these fibers reach the sweat glands in the facial skin. By this means, a stimulus intended for saliva production produces sweat secretion instead. P.788

Figure 11-85 Parotid gland and its relations. A. Lateral surface of the gland and the course of the parotid duct. B. Horizontal section of the parotid gland.

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Submandibular Gland The submandibular gland consists of a mixture of serous and mucous acini. It lies beneath the lower border of the body of the mandible (Fig. 11-86) and is divided into superficial and deep parts by the mylohyoid muscle. The deep part of the gland lies beneath the mucous membrane of the mouth on the side of the tongue. The submandibular duct emerges from the anterior end of the deep part of the gland and runs forward beneath the mucous membrane of the mouth. It opens into the mouth on a small papilla, which is situated at the side of the frenulum of the tongue (Fig. 11-72). Nerve Supply Parasympathetic secretomotor supply is from the facial nerve via the chorda tympani, and the submandibular ganglion. The postganglionic fibers pass directly to the gland. Clinical Notes Submandibular Salivary Gland: Calculus Formation The submandibular salivary gland is a common site of calculus formation. This condition is rare in the other salivary glands. The presence of a tense swelling below the body of the mandible, which is greatest before or during a meal and is reduced in size or absent between meals, is diagnostic of the condition. Examination of the floor of the mouth will reveal absence of ejection of saliva from the orifice of the duct of the affected gland. Frequently, the stone can be palpated in the duct, which lies below the mucous membrane of the floor of the mouth. Enlargement of the Submandibular Lymph Nodes and Swelling of the Submandibular Salivary Gland The submandibular lymph nodes are commonly enlarged as a result of a pathologic condition of the scalp, face, maxillary sinus, or mouth cavity. One of the most common causes of painful enlargement of these nodes is acute infection of the teeth. Enlargement of these nodes should not be confused with pathologic swelling of the submandibular salivary gland. Sublingual Gland The sublingual gland lies beneath the mucous membrane (sublingual fold) of the floor of the mouth, close to the frenulum of the tongue (Fig. 11-86). It has both serous and mucous acini, with the latter predominating. The sublingual ducts (8 to 20 in number) open into the mouth on the summit of the sublingual fold (Fig. 11-72). Nerve Supply Parasympathetic secretomotor supply is from the facial nerve via the chorda tympani, and the submandibular ganglion. Postganglionic fibers pass directly to the gland. Clinical Notes Sublingual Salivary Gland and Cyst Formation The sublingual salivary gland, which lies beneath the sublingual fold of the floor of the mouth, opens into the mouth by numerous small ducts. Blockage of one of these ducts is believed to be the cause of cysts under the tongue. The Pharynx The pharynx is situated behind the nasal cavities, the mouth, and the larynx (Fig. 11-87) and may be divided into nasal, oral, and laryngeal parts. The pharynx is funnel shaped, its upper, wider end lying under the skull and its lower, narrow end becoming continuous with the esophagus opposite the sixth cervical vertebra. The pharynx has a musculomembranous wall, which is deficient anteriorly. Here, it is replaced by the posterior openings into the nose (choanae), the opening into the mouth, and the inlet of the larynx. By means of the auditory tube, the mucous membrane is also continuous with that of the tympanic cavity. Muscles of the Pharynx The muscles in the wall of the pharynx consist of the superior, middle, and inferior constrictor muscles (Fig. 11-80A), whose fibers run in a somewhat circular direction, and the stylopharyngeus and salpingopharyngeus muscles, whose fibers run in a somewhat longitudinal direction. The three constrictor muscles extend around the pharyngeal wall to be inserted into a fibrous band or raphe that extends from the pharyngeal tubercle on the basilar part of the occipital bone of the skull down to the esophagus. The three constrictor muscles overlap each other so that the middle constrictor lies on the outside of the lower part of the superior constrictor and the inferior constrictor lies outside the lower part of the middle constrictor (Fig. 11-88). The lower part of the inferior constrictor, which arises from the cricoid cartilage, is called the cricopharyngeus muscle (Fig. 11-88). The fibers of the cricopharyngeus pass horizontally around the lowest and narrowest part of the pharynx and act as a sphincter. Killian’s dehiscence is the area on the posterior pharyngeal wall between the upper propulsive part of the inferior constrictor and the lower sphincteric part, the cricopharyngeus. The details of the origins, insertions, nerve supply, and actions of the pharyngeal muscles are summarized in Table 11-10. Interior of the Pharynx The pharynx is divided into three parts: the nasal pharynx, the oral pharynx, and the laryngeal pharynx. P.790

Figure 11-86 A. Submandibular and sublingual salivary glands (lateral view). B. Coronal section through the superficial and deep parts of the submandibular salivary glands. C. Coronal section (anterior to B) through the sublingual salivary glands and the ducts of the submandibular salivary glands.

Nasal Pharynx This lies above the soft palate and behind the nasal cavities (Fig. 11-87). In the submucosa of the roof is a collection of lymphoid tissue called the pharyngeal tonsil (Fig. 11-89). The pharyngeal isthmus is the opening in the floor between the soft palate and the posterior pharyngeal wall. On the lateral wall is the opening of the auditory tube, the elevated ridge of which is called the tubal elevation (Fig. 11-89). The pharyngeal recess is a depression in the pharyngeal wall behind the tubal elevation. The salpingopharyngeal fold is a vertical fold of mucous membrane covering the salpingopharyngeus muscle. Oral Pharynx This lies behind the oral cavity (Fig. 11-87). The floor is formed by the posterior one third of the tongue and the interval between the tongue and epiglottis. In the midline is the median glossoepiglottic fold (Fig. 11-77), and on each side the lateral glossoepiglottic fold. The depression on each side of the median glossoepiglottic fold is called the vallecula (Fig. 11-77). On the lateral wall on each side are the palatoglossal and the palatopharyngeal arches or folds and the palatine tonsils between them (Fig. 11-89). The palatoglossal arch is a fold of mucous membrane covering the palatoglossus muscle. The P.791
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interval between the two palatoglossal arches is called the oropharyngeal isthmus and marks the boundary between the mouth and pharynx. The palatopharyngeal arch is a fold of mucous membrane covering the palatopharyngeus muscle. The recess between the palatoglossal and palatopharyngeal arches is occupied by the palatine tonsil.

Figure 11-87 Sagittal section through the nose, mouth, pharynx, and larynx to show the subdivisions of the pharynx.
Figure 11-88 The pharynx seen from behind. A. Note the three constrictor muscles and the position of the stylopharyngeus muscles. B. The greater part of the posterior wall of the pharynx has been removed to display the nasal, oral, and laryngeal parts of the pharynx.
Table 11-10 Muscles of the Pharynx
Muscle Origin Insertion Nerve Supply Action
Superior constrictor Medial pterygoid plate, pterygoid hamulus, pterygomandibular ligament, mylohyoid line of mandible Pharyngeal tubercle of occipital bone, raphe in midline posteriorly Pharyngeal plexus Aids soft palate in closing off nasal pharynx, propels bolus downward
Middle constrictor Lower part of stylohyoid ligament, lesser and greater cornu of hyoid bone Pharyngeal raphe Pharyngeal plexus Propels bolus downward
Inferior constrictor Lamina of thyroid cartilage, cricoid cartilage Pharyngeal raphe Pharyngeal plexus Propels bolus downward
Cricopharyngeus Lowest fibers of inferior constrictor muscle     Sphincter at lower end of pharynx
Stylopharyngeus Styloid process of temporal bone Posterior border of thyroid cartilage Glossopharyngeal nerve Elevates larynx during swallowing
Salpingopharyngeus Auditory tube Blends with palatopharyngeus Pharyngeal plexus Elevates pharynx
Palatopharyngeus Palatine aponeurosis Posterior border of thyroid cartilage Pharyngeal plexus Elevates wall of pharynx, pulls palatopharyngeal arch medially
Figure 11-89 Sagittal section of the head and neck, showing the relations of the nasal cavity, mouth, pharynx, and larynx.

Clinical Notes The Lymphoid Tissue of the Pharynx At the junction of the mouth with the oral part of the pharynx, and the nose with the nasal part of the pharynx, are collections of lymphoid tissue of considerable clinical importance. The palatine tonsils and the nasopharyngeal tonsils are the most important. Tonsils and Tonsillitis The palatine tonsils reach their maximum normal size in early childhood. After puberty, together with other lymphoid tissues in the body, they gradually atrophy. The palatine tonsils are a common site of infection, producing the characteristic sore throat and pyrexia. The deep cervical lymph node situated below and behind the angle of the mandible, which drains lymph from this organ, is usually enlarged and tender. Recurrent attacks of tonsillitis are best treated by tonsillectomy. After tonsillectomy, the external palatine vein, which lies lateral to the tonsil, may be the source of troublesome postoperative bleeding. Quinsy A peritonsillar abscess (quinsy) is caused by spread of infection from the palatine tonsil to the loose connective tissue outside the capsule (Fig. 11-90). The nasopharyngeal tonsil or pharyngeal tonsil consists of a collection of lymphoid tissue beneath the epithelium of the roof of the nasal part of the pharynx. Like the palatine tonsil, it is largest in early childhood and starts to atrophy after puberty. Adenoids Excessive hypertrophy of the lymphoid tissue, usually associated with infection, causes the pharyngeal tonsils to become enlarged; they are then commonly referred to as adenoids. Marked hypertrophy blocks the posterior nasal openings and causes the patient to snore loudly at night and to breathe through the open mouth. The close relationship of the infected lymphoid tissue to the auditory tube may be the cause of deafness and recurrent otitis media. Adenoidectomy is the treatment of choice for hypertrophied adenoids with infection. The nasal part of the pharynx may be viewed clinically by a mirror passed through the mouth (Fig. 11-91). Laryngeal Pharynx This lies behind the opening into the larynx (Fig. 11-87). The lateral wall is formed by the thyroid cartilage and the thyrohyoid membrane. The piriform fossa is a depression in the mucous membrane on each side of the laryngeal inlet (Fig. 11-88). Sensory Nerve Supply of the Pharyngeal Mucous Membrane

  • Nasal pharynx: The maxillary nerve (V2)
  • Oral pharynx: The glossopharyngeal nerve
  • Laryngeal pharynx (around the entrance into the larynx): The internal laryngeal branch of the vagus nerve

Blood Supply of the Pharynx Ascending pharyngeal, tonsillar branches of facial arteries, and branches of maxillary and lingual arteries Lymph Drainage of the Pharynx Directly into the deep cervical lymph nodes or indirectly via the retropharyngeal or paratracheal nodes into the deep cervical nodes Clinical Notes Piriform Fossa and Foreign Bodies The piriform fossa is a recess of mucous membrane situated on either side of the entrance of the larynx. It is bounded medially by the aryepiglottic folds and laterally by the thyroid cartilage. Clinically, it is important because it is a common site for the lodging of sharp ingested bodies such as fish bones. The presence of such a foreign body immediately causes the patient to gag violently. Once the object has become jammed, it is difficult for the patient to remove it without a physician’s assistance. Pharyngeal Pouch Examination of the lower part of the posterior surface of the inferior constrictor muscle reveals a potential gap between the upper oblique and the lower horizontal fibers (cricopharyngeus). This area is marked by a dimple in the lining mucous membrane. It is believed that the function of the cricopharyngeus is to prevent the entry of air into the esophagus. Should the cricopharyngeus fail to relax during swallowing, the internal pharyngeal pressure may rise and force the mucosa and submucosa of the dimple posteriorly, to produce a diverticulum. Once the diverticulum has been formed, it may gradually enlarge and fill with food with each meal. Unable to expand posteriorly because of the vertebral column, it turns downward, usually on the left side. The presence of the pouch filled with food causes difficulty in swallowing (dysphagia). Cervical Tuberculous Osteomyelitis and the Pharynx Pus arising from tuberculosis of the upper cervical vertebrae is limited in front by the prevertebral layer of deep fascia. A midline swelling is formed and bulges forward in the posterior wall of the pharynx. The pus then tracks laterally and downward behind the carotid sheath to reach the posterior triangle. Here, the fascia, which forms a covering to the muscular floor of the triangle, is weaker, and the abscess points behind the sternocleidomastoid. Rarely, the abscess may track downward behind the prevertebral fascia to reach the superior and posterior mediastina in the thorax. It is important to distinguish this condition from an abscess involving the retropharyngeal lymph nodes. These nodes lie in front of the prevertebral layer of fascia but behind the fascia, which covers the outer surface of the constrictor muscles. Such an abscess usually points on the posterior pharyngeal wall and, if untreated, ruptures into the pharyngeal cavity. P.794

Figure 11-90 Horizontal section through the mouth and the oral pharynx. Left, the normal palatine tonsil and its relationships. Right, the position of a peritonsillar abscess. Note the relationship of the abscess to the superior constrictor muscle and the carotid sheath. The opening into the larynx can also be seen below and behind the tongue.
Figure 11-91 A. Sagittal section through the nose, mouth, larynx, and pharynx showing the position of the mirror in posterior rhinoscopy. B. Structures seen in posterior rhinoscopy.

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The Process of Swallowing (Deglutition) Masticated food is formed into a ball or bolus on the dorsum of the tongue and voluntarily pushed upward and backward against the undersurface of the hard palate. This is brought about by the contraction of the styloglossus muscles on both sides, which pull the root of the tongue upward and backward. The palatoglossus muscles then squeeze the bolus backward into the pharynx. From this point onward the process of swallowing becomes an involuntary act. The nasal part of the pharynx is now shut off from the oral part of the pharynx by the elevation of the soft palate, the pulling forward of the posterior wall of the pharynx by the upper fibers of the superior constrictor muscle, and the contraction of the palatopharyngeus muscles. This prevents the passage of food and drink into the nasal cavities. The larynx and the laryngeal part of the pharynx are pulled upward by the contraction of the stylopharyngeus, salpingopharyngeus, thyrohyoid, and palatopharyngeus muscles. The main part of the larynx is thus elevated to the posterior surface of the epiglottis, and the entrance into the larynx is closed. The laryngeal entrance is made smaller by the approximation of the aryepiglottic folds, and the arytenoid cartilages are pulled forward by the contraction of the aryepiglottic, oblique arytenoid, and thyroarytenoid muscles. The bolus moves downward over the epiglottis, the closed entrance into the larynx, and reaches the lower part of the pharynx as the result of the successive contraction of the superior, middle, and inferior constrictor muscles. Some of the food slides down the groove on either side of the entrance into the larynx, that is, down through the piriform fossae. Finally, the lower part of the pharyngeal wall (the cricopharyngeus muscle) relaxes and the bolus enters the esophagus. Palatine Tonsils The palatine tonsils are two masses of lymphoid tissue, each located in the depression on the lateral wall of the oral part of the pharynx between the palatoglossal and palatopharyngeal arches (Fig. 11-90). Each tonsil is covered by mucous membrane, and its free medial surface projects into the pharynx. The surface is pitted by numerous small openings that lead into the tonsillar crypts. The tonsil is covered on its lateral surface by a fibrous capsule (Fig. 11-90). The capsule is separated from the superior constrictor muscle by loose areolar tissue (Fig. 11-90) and the external palatine vein descends from the soft palate in this tissue to join the pharyngeal venous plexus. Lateral to the superior constrictor muscle lie the styloglossus muscle, the loop of the facial artery, and the internal carotid artery. The tonsil reaches its maximum size during early childhood, but after puberty it diminishes considerably in size. Blood Supply The tonsillar branch of the facial artery. The veins pierce the superior constrictor muscle and join the external palatine, the pharyngeal, or the facial veins. Lymph Drainage of the Tonsil The upper deep cervical lymph nodes, just below and behind the angle of the mandible Waldeyer’s Ring of Lymphoid Tissue The lymphoid tissue that surrounds the opening into the respiratory and digestive systems forms a ring. The lateral part of the ring is formed by the palatine tonsils and tubal tonsils (lymphoid tissue around the opening of the auditory tube in the lateral wall of the nasopharynx). The pharyngeal tonsil in the roof of the nasopharynx forms the upper part, and the lingual tonsil on the posterior third of the tongue forms the lower part. The Esophagus The esophagus is a muscular tube about 10 in. (25 cm) long, extending from the pharynx to the stomach (Figs. 11-13 and 11-88). It begins at the level of the cricoid cartilage, opposite the body of the sixth cervical vertebra. It commences in the midline, but as it descends through the neck, it inclines to the left side. Its further course in the thorax is described on page 128. Relations in the Neck

  • Anteriorly: The trachea; the recurrent laryngeal nerves ascend one on each side, in the groove between the trachea and the esophagus (Fig. 11-49).
  • Posteriorly: The prevertebral layer of deep cervical fascia, the longus colli, and the vertebral column (Fig. 11-49)
  • Laterally: On each side lie the lobe of the thyroid gland and the carotid sheath (Fig. 11-49)

Blood Supply in the Neck The arteries of the esophagus in the neck are derived from the inferior thyroid arteries. The veins drain into the inferior thyroid veins. Lymph Drainage in the Neck The lymph vessels drain into the deep cervical lymph nodes. Nerve Supply in the Neck The nerves are derived from the recurrent laryngeal nerves and from the sympathetic trunks. The Respiratory System in the Head and Neck The Nose The nose consists of the external nose and the nasal cavity, both of which are divided by a septum into right and left halves. External Nose The external nose has two elliptical orifices called the nostrils, which are separated from each other by the nasal septum (Fig. 11-92). The lateral margin, the ala nasi, is rounded and mobile. The framework of the external nose is made up above by the nasal bones, the frontal processes of the maxillae, and the nasal part of the frontal bone. Below, the framework is formed of plates of hyaline cartilage (Fig. 11-92). P.796

Figure 11-92 External nose and nasal septum. A. Lateral view of bony and cartilaginous skeleton of external nose. B. Anterior view of bony and cartilaginous skeleton of external nose. C. Bony and cartilaginous skeleton of nasal septum.

Blood Supply of the External Nose The skin of the external nose is supplied by branches of the ophthalmic and the maxillary arteries (see page 750). The skin of the ala and the lower part of the septum are supplied by branches from the facial artery. Nerve Supply of the External Nose The infratrochlear and external nasal branches of the ophthalmic nerve (CN V) and the infraorbital branch of the maxillary nerve (CN V) (see pages 760 and 761). Nasal Cavity The nasal cavity extends from the nostrils in front to the posterior nasal apertures or choanae behind, where the nose opens into the nasopharynx. The nasal vestibule is the area of the nasal cavity lying just inside the nostril (Fig. 11-93). The nasal cavity is divided into right and left halves by the nasal septum (Fig. 11-92). The septum is made up of the septal cartilage, the vertical plate of the ethmoid, and the vomer. Walls of the Nasal Cavity Each half of the nasal cavity has a floor, a roof, a lateral wall, and a medial or septal wall. Floor The palatine process of the maxilla and the horizontal plate of the palatine bone (Fig. 11-92) Roof The roof is narrow and is formed anteriorly beneath the bridge of the nose by the nasal and frontal bones, in the middle by the cribriform plate of the ethmoid, located beneath the anterior cranial fossa, and posteriorly by the downward sloping body of the sphenoid (Fig. 11-93). Lateral Wall The lateral wall has three projections of bone called the superior, middle, and inferior nasal conchae (Fig. 11-93). The space below each concha is called a meatus. P.797

Figure 11-93 A. Lateral wall of the right nasal cavity. B. Lateral wall of the right nasal cavity; the superior, middle, and inferior conchae have been partially removed to show openings of the paranasal sinuses and the nasolacrimal duct into the meati.

Sphenoethmoidal Recess The sphenoethmoidal recess is a small area above the superior concha. It receives the opening of the sphenoid air sinus (Fig. 11-93). Superior Meatus The superior meatus lies below the superior concha (Fig. 11-93). It receives the openings of the posterior ethmoid sinuses. Middle Meatus The middle meatus lies below the middle concha. It has a rounded swelling called the bulla ethmoidalis that is formed by the middle ethmoidal air sinuses, which open on its upper border. A curved opening, the hiatus semilunaris, lies just below the bulla (Fig. 11-93). The anterior end of the hiatus leads into a funnel-shaped channel called the infundibulum, which is continuous with the frontal sinus. The maxillary sinus opens into the middle meatus through the hiatus semilunaris. Inferior Meatus The inferior meatus lies below the inferior concha and receives the opening of the lower end of the nasolacrimal duct, which is guarded by a fold of mucous membrane (Fig. 11-93). Medial Wall The medial wall is formed by the nasal septum. The upper part is formed by the vertical plate of the ethmoid and the vomer (Fig. 11-92). The anterior part is formed by the septal cartilage. The septum rarely lies in the midline, thus increasing the size of one half of the nasal cavity and decreasing the size of the other. Mucous Membrane of the Nasal Cavity The vestibule is lined with modified skin and has coarse hairs. The area above the superior concha is lined with olfactory mucous membrane and contains nerve endings sensitive to the reception of smell. The lower part of the nasal cavity is lined with respiratory mucous membrane. A large plexus of veins in the submucous connective tissue is present in the respiratory region. P.798
Function of Warm Blood and Mucus of Mucous Membrane The presence of warm blood in the venous plexuses serves to heat up the inspired air as it enters the respiratory system. The presence of mucus on the surfaces of the conchae traps foreign particles and organisms in the inspired air, which are then swallowed and destroyed by gastric acid. Nerve Supply of the Nasal Cavity. The olfactory nerves from the olfactory mucous membrane ascend through the cribriform plate of the ethmoid bone to the olfactory bulbs (Fig. 11-94). The nerves of ordinary sensation are branches of the ophthalmic division (V1) and the maxillary division (V2) of the trigeminal nerve (Fig. 11-94). Blood Supply to the Nasal Cavity The arterial supply to the nasal cavity is from branches of the maxillary artery, one of the terminal branches of the external carotid artery. The most important branch is the sphenopalatine artery (Fig. 11-95). The sphenopalatine artery anastomoses with the septal branch of the superior labial branch of the facial artery in the region of the vestibule. The submucous venous plexus is drained by veins that accompany the arteries. Lymph Drainage of the Nasal Cavity The lymph vessels draining the vestibule end in the submandibular nodes. The remainder of the nasal cavity is drained by vessels that pass to the upper deep cervical nodes. Clinical Notes Examination of the Nasal Cavity Examination of the nasal cavity may be carried out by inserting a speculum through the external nares or by means of a mirror in the pharynx. In the latter case, the choanae and the posterior border of the septum can be visualized (Fig. 11-91). It should be remembered that the nasal septum is rarely situated in the midline. A severely deviated septum may interfere with drainage of the nose and the paranasal sinuses. Trauma to the Nose Fractures involving the nasal bones are common. Blows directed from the front may cause one or both nasal bones to be displaced downward and inward. Lateral fractures also occur in which one nasal bone is driven inward and the other outward; the nasal septum is usually involved. Infection of the Nasal Cavity Infection of the nasal cavity can spread in a variety of directions. The paranasal sinuses are especially prone to infection. Organisms may spread via the nasal part of the pharynx and the auditory tube to the middle ear. It is possible for organisms to ascend to the meninges of the anterior cranial fossa, along the sheaths of the olfactory nerves through the cribriform plate, and produce meningitis. Foreign Bodies in the Nose Foreign bodies in the nose are common in children. The presence of the nasal septum and the existence of the folded, shelflike conchae make impaction and retention of balloons, peas, and small toys relatively easy. Nose Bleeding Epistaxis, or bleeding from the nose, is a frequent condition. The most common cause is nose picking. The bleeding may be arterial or venous, and most episodes occur on the anteroinferior portion of the septum and involve the septal branches of the sphenopalatine and facial vessels. Embryologic Notes Development of the Nose The roof of the nose is formed from the lateral nasal processes, from which the lateral walls also are formed, with the assistance of the maxillary processes (Fig. 11-43). The anterior openings of the nose begin as olfactory pits in the frontonasal process. Each olfactory pit is bounded medially by the medial nasal process, laterally by the lateral nasal process, and inferiorly by the maxillary process. As these processes fuse, the olfactory pits become deeper and form well-defined blind sacs, the opening into each of which is the nostril. The floor of the nose at first is very short and consists of the medial nasal process and the anterior part of the maxillary process on each side. At this stage, the floors of the olfactory pits rupture so that the nasal cavities communicate with the developing mouth (Fig. 11-82). Meanwhile, the nasal septum is forming as a downgrowth from the medial nasal process (Fig. 11-82). Later, the palatal processes of the maxilla grow medially and fuse with each other and with the nasal septum, thus completing the floor of the nose. Each nasal cavity therefore communicates anteriorly with the exterior through the nostril and posteriorly through the choana with the nasopharynx. In the early stages of development, the nose is a much-flattened structure and gains its recognizable form only after the facial development is complete. Median Nasal Furrow In median nasal furrow, the nasal septum is split, separating the two halves of the nose (Fig. 11-96A). Lateral Proboscis In lateral proboscis, a skin-covered process develops, usually with a dimple at its lower end (Fig. 11-96B). P.799

Figure 11-94 A. Lateral wall of nasal cavity showing sensory innervation of mucous membrane. B. Nasal septum showing sensory innervation of mucous membrane.

The Paranasal Sinuses The paranasal sinuses are cavities found in the interior of the maxilla, frontal, sphenoid, and ethmoid bones (Fig. 11-97). They are lined with mucoperiosteum and filled with air; they communicate with the nasal cavity through relatively small apertures. The maxillary and sphenoidal sinuses are present in a rudimentary form at birth; they enlarge appreciably after the eighth year and become fully formed in adolescence. Drainage of Mucus and Function of Paranasal Sinuses The mucus produced by the mucous membrane is moved into the nose by ciliary action of the columnar cells. Drainage of the mucus is also achieved by the siphon action created during the blowing of the nose. The function of the sinuses is to act as resonators to the voice; they also reduce the weight of the skull. When the apertures of the sinuses are blocked or they become filled with fluid, the quality of the voice is markedly changed. Maxillary Sinus The maxillary sinus is pyramidal in shape and located within the body of the maxilla behind the skin of the cheek (Fig. 11-97). The roof is formed by the floor of the orbit, and the floor is related to the roots of the premolars and molar teeth. The maxillary sinus opens into the middle meatus of the nose through the hiatus semilunaris (Fig. 11-97). Frontal Sinuses The two frontal sinuses are contained within the frontal bone (Fig. 11-97). They are separated from each other by a bony septum. Each sinus is roughly triangular, extending upward above the medial end of the eyebrow and backward into the medial part of the roof of the orbit. P.800

Figure 11-95 A. Lateral wall of nasal cavity showing the arterial supply of the mucous membrane. B. Nasal septum showing the arterial supply of the mucous membrane.

Each frontal sinus opens into the middle meatus of the nose through the infundibulum (Fig. 11-93). Sphenoidal Sinuses The two sphenoidal sinuses lie within the body of the sphenoid bone (Fig. 11-97). Each sinus opens into the sphenoethmoidal recess above the superior concha. Ethmoid Sinuses The ethmoidal sinuses are anterior, middle, and posterior and they are contained within the ethmoid bone, between the nose and the orbit (Fig. 11-97). They are separated from the latter by a thin plate of bone so that infection can readily spread from the sinuses into the orbit. The anterior sinuses open into the infundibulum; the middle sinuses open into the middle meatus, on or above the bulla ethmoidalis; and the posterior sinuses open into the superior meatus. The various sinuses and their openings into the nose are summarized in Table 11-11. Clinical Notes Sinusitis and the Examination of the Paranasal Sinuses Infection of the paranasal sinuses is a common complication of nasal infections. Rarely, the cause of maxillary sinusitis is extension from an apical dental abscess. The frontal, ethmoidal, and maxillary sinuses can be palpated clinically for areas of tenderness. The frontal sinus can be examined by pressing the finger upward beneath the medial end of the superior orbital margin. Here the floor of the frontal sinus is closest to the surface. The ethmoidal sinuses can be palpated by pressing the finger medially against the medial wall of the orbit. The maxillary sinus can be examined for tenderness by pressing the finger against the anterior wall of the maxilla below the inferior orbital margin; pressure over the infraorbital nerve may reveal increased sensitivity. Directing the beam of a flashlight either through the roof of the mouth or through the cheek in a darkened room will often enable a physician to determine whether the maxillary sinus is full of inflammatory fluid rather than air. This method of transillumination is simple and effective. Radiologic examination of the sinuses is also most helpful in making a diagnosis. One should always compare the clinical findings of each sinus on the two sides of the body. The frontal sinus is innervated by the supraorbital nerve, which also supplies the skin of the forehead and scalp as far back as the vertex. It is, therefore, not surprising that patients with frontal sinusitis have pain referred over this area. The maxillary sinus is innervated by the infraorbital nerve and, in this case, pain is referred to the upper jaw, including the teeth. The frontal sinus drains into the hiatus semilunaris, via the infundibulum, close to the orifice of the maxillary sinus on the lateral wall of the nose. It is thus not unexpected to find that a patient with frontal sinusitis nearly always has a maxillary sinusitis. The maxillary sinus is particularly prone to infection because its drainage orifice through the hiatus semilunaris is badly placed near the roof of the sinus. In other words, the sinus has to fill up with fluid before it can effectively drain with the person in the upright position. The relation of the apices of the roots of the teeth in the maxilla to the floor of the maxillary sinus was already emphasized. P.801

Figure 11-96 A. Median nasal furrow in which the nasal septum has completely split, separating the two halves of the nose. Note that the external nares are separated by a wide furrow. (Courtesy of L. Thompson.) B. Lateral proboscis. (Courtesy of R. Chase.)
Figure 11-97 A. The position of the paranasal sinuses in relation to the face. B. Coronal section through the nasal cavity showing the ethmoidal and the maxillary sinuses.

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Table 11-11 Paranasal Sinuses and Their Site of Drainage Into the Nosea
Sinus Site of Drainage
Maxillary sinus Middle meatus through hiatus semilunaris
Frontal sinuses Middle meatus via infundibulum
Sphenoidal sinuses Sphenoethmoidal recess
Ethmoidal sinuses
    Anterior group Infundibulum and into middle meatus
    Middle group Middle meatus on or above bulla ethmoidalis
    Posterior group Superior meatus
aNote that maxillary and sphenoidal sinuses are present in rudimentary form at birth, enlarge appreciably after the eighth year, and are fully formed in adolescence.

Crossing of Air and Food Pathways in the Pharynx It is in the pharynx that the air and food pathways cross. This is made possible by the presence of the soft palate, which serves as a flap-valve. This flap shuts off the mouth from the oropharynx, for example, during the process of chewing food so that breathing may continue unaffected. The completely raised soft palate can shut off the nasopharynx from the oropharynx, thus preventing food entering the nasopharynx in swallowing (see page 795). When it is desirable to direct the maximum amount of air in and out of the larynx, the soft palate is raised to direct air through the mouth rather than the narrow cavities of the nose. Such an arrangement permits the expectoration of mucus from the respiratory system through the mouth. It also allows the maximum expiration of air through the mouth as in the use of wind instruments such as the trumpet. The Larynx The larynx is an organ that provides a protective sphincter at the inlet of the air passages and is responsible for voice production. It is situated below the tongue and hyoid bone and between the great blood vessels of the neck and lies at the level of the fourth, fifth, and sixth cervical vertebrae (Fig. 11-87). It opens above into the laryngeal part of the pharynx, and below is continuous with the trachea. The larynx is covered in front by the infrahyoid strap muscles and at the sides by the thyroid gland. The framework of the larynx is formed of cartilages that are held together by ligaments and membranes, moved by muscles, and lined by mucous membrane. Cartilages of the Larynx

  • Thyroid cartilage: This is the largest cartilage of the larynx (Fig. 11-98) and consists of two laminae of hyaline cartilage that meet in the midline in the prominent V angle (the so-called Adam’s apple). The posterior border extends upward into a superior cornu and downward into an inferior cornu. On the outer surface of each lamina is an oblique line for the attachment of muscles.
  • Cricoid cartilage: This cartilage is formed of hyaline cartilage and shaped like a signet ring, having a broad plate behind and a shallow arch in front (Fig. 11-98). The cricoid cartilage lies below the thyroid cartilage, and on each side of the lateral surface is a facet for articulation with the inferior cornu of the thyroid cartilage. Posteriorly, the lamina has on its upper border on each side a facet for articulation with the arytenoid cartilage. All these joints are synovial.
  • Arytenoid cartilages: There are two arytenoid cartilages, which are small and pyramid shaped and located at the back of the larynx (Fig. 11-98). They articulate with the upper border of the lamina of the cricoid cartilage. Each cartilage has an apex above that articulates with the small corniculate cartilage, a base below that articulates with the lamina of the cricoid cartilage, and a vocal process that projects forward and gives attachment to the vocal ligament. A muscular process that projects laterally gives attachment to the posterior and lateral cricoarytenoid muscles.
  • Corniculate cartilages: Two small conical-shaped cartilages articulate with the arytenoid cartilages (Fig. 11-99). They give attachment to the aryepiglottic folds.
  • Cuneiform cartilages: These two small rod-shaped cartilages are found in the aryepiglottic folds and serve to strengthen them (Fig. 11-99).
  • Epiglottis: This leaf-shaped lamina of elastic cartilage lies behind the root of the tongue (Fig. 11-98). Its stalk is attached to the back of the thyroid cartilage. The sides of the epiglottis are attached to the arytenoid cartilages by the aryepiglottic folds of mucous membrane. The upper edge of the epiglottis is free. The covering of mucous membrane passes forward onto the posterior surface of the tongue as the median glossoepiglottic fold; the depression on each side of the fold is called the vallecula (Fig. 11-90). Laterally the mucous membrane passes onto the wall of the pharynx as the lateral glossoepiglottic fold.

Membranes and Ligaments of the Larynx

  • Thyrohyoid membrane: This connects the upper margin of the thyroid cartilage to the hyoid bone (Fig. 11-98). In the midline it is thickened to form the median thyrohyoid ligament. The membrane is pierced on each side by the superior laryngeal vessels and the internal laryngeal nerve, a branch of the superior laryngeal nerve (Fig. 11-80).
  • Cricotracheal ligament: This connects the cricoid cartilage to the first ring of the trachea (Fig. 11-98).
  • Quadrangular membrane: This extends between the epiglottis and the arytenoid cartilages (Fig. 11-99). Its thickened inferior margin forms the vestibular ligament, and the vestibular ligaments form the interior of the vestibular folds (Fig. 11-99). P.803
    Figure 11-98 The larynx and its ligaments from the front (A), from the lateral aspect (B), and from behind (C). D. The left lamina of thyroid cartilage has been removed to display the interior of the larynx.

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    Figure 11-99 A. Muscles of the larynx seen from behind. B. Coronal section through the larynx. C. Rima glottidis partially open as in quiet breathing. D. Rima glottidis wide open as in deep breathing. E. Muscles that move vocal ligaments.
  • P.805

  • Cricothyroid ligament: The lower margin is attached to the upper border of the cricoid cartilage (Fig. 11-99). The superior margin of the ligament, instead of being attached to the thyroid cartilage, ascends on the medial surface of the thyroid cartilage. Its upper free margin, composed almost entirely of elastic tissue, forms the important vocal ligament on each side. The vocal ligaments form the interior of the vocal folds (vocal cords) (Fig. 11-99). The anterior end of each vocal ligament is attached to the thyroid cartilage, and the posterior end is attached to the vocal process of the arytenoid cartilage.

Inlet of the Larynx The inlet of the larynx looks backward and upward into the laryngeal part of the pharynx (Fig. 11-88). The opening is wider in front than behind and is bounded in front by the epiglottis, laterally by the aryepiglottic fold of mucous membrane, and posteriorly by the arytenoid cartilages with the corniculate cartilages. The cuneiform cartilage lies within and strengthens the aryepiglottic fold and produces a small elevation on the upper border. The Piriform Fossa The piriform fossa is a recess on either side of the fold and inlet (Fig. 11-99). It is bounded medially by the aryepiglottic fold and laterally by the thyroid cartilage and the thyrohyoid membrane. Laryngeal Folds Vestibular Fold The vestibular fold is a fixed fold on each side of the larynx (Fig. 11-98). It is formed by mucous membrane covering the vestibular ligament and is vascular and pink in color. Vocal Fold (Vocal Cord) The vocal fold is a mobile fold on each side of the larynx and is concerned with voice production. It is formed by mucous membrane covering the vocal ligament and is avascular and white in color. The vocal fold moves with respiration and its white color is easily seen when viewed with a laryngoscope (Fig. 11-99). The gap between the vocal folds is called the rima glottidis or glottis (Fig. 11-99). The glottis is bounded in front by the vocal folds and behind by the medial surface of the arytenoid cartilages. The glottis is the narrowest part of the larynx and measures about 2.5 cm from front to back in the male adult and less in the female. In children the lower part of the larynx within the cricoid cartilage is the narrowest part. Cavity of the Larynx The cavity of the larynx extends from the inlet to the lower border of the cricoid cartilage, where it is continuous with the cavity of the trachea. It is divided into three regions:

  • The vestibule, which is situated between the inlet and the vestibular folds
  • The middle region, which is situated between the vestibular folds above and the vocal folds below
  • The lower region, which is situated between the vocal folds above and the lower border of the cricoid cartilage below

Sinus of the Larynx The sinus of the larynx is a small recess on each side of the larynx situated between the vestibular and vocal folds. It is lined with mucous membrane (Fig. 11-99). Saccule of the Larynx The saccule of the larynx is a diverticulum of mucous membrane that ascends from the sinus (Fig. 11-99). The mucous secretion lubricates the vocal cords. Muscles of the Larynx The muscles of the larynx may be divided into two groups: extrinsic and intrinsic. Extrinsic Muscles These muscles move the larynx up and down during swallowing. Note that many of these muscles are attached to the hyoid bone, which is attached to the thyroid cartilage by the thyrohyoid membrane. It follows that movements of the hyoid bone are accompanied by movements of the larynx.

  • Elevation: The digastric, the stylohyoid, the mylohyoid, the geniohyoid, the stylopharyngeus, the salpingopharyngeus, and the palatopharyngeus muscles
  • Depression: The sternothyroid, the sternohyoid, and the omohyoid muscles

Intrinsic Muscles Two muscles modify the laryngeal inlet (Fig. 11-99):

  • Narrowing the inlet: The oblique arytenoid muscle
  • Widening the inlet: The thyroepiglottic muscle

Five muscles move the vocal folds (cords) (Fig. 11-99):

  • Tensing the vocal cords: The cricothyroid muscle
  • Relaxing the vocal cords: The thyroarytenoid (vocalis) muscle
  • Adducting the vocal cords: The lateral cricoarytenoid muscle
  • Abducting the vocal cords: The posterior cricoarytenoid muscle
  • Approximates the arytenoid cartilages: The transverse arytenoid muscle

The details of the origins, insertions, nerve supply, and action of the intrinsic muscles of the larynx are given in Table 11-12. Movements of the Vocal Folds (Cords) The movements of the vocal folds depend on the movements of the arytenoid cartilages, which rotate and slide up and down on the sloping shoulder of the superior border of the cricoid cartilage. The rima glottidis is opened by the contraction of the posterior cricoarytenoid, which rotates the arytenoid cartilage and abducts the vocal process (Fig. 11-99). The elastic tissue in the capsules of the cricoarytenoid joints keeps the arytenoid cartilages apart so that the posterior part of the glottis is open. P.806

Table 11-12 Intrinsic Muscles of the Larynx
Muscle Origin Insertion Nerve Supply Action
Muscles Controlling the Laryngeal Inlet
Oblique arytenoid Muscular process of arytenoid cartilage Apex of opposite arytenoid cartilage Recurrent laryngeal nerve Narrows the inlet by bringing the aryepiglottic folds together
Thyroepiglottic Medial surface of thyroid cartilage Lateral margin of epiglottis and aryepiglottic fold Recurrent laryngeal nerve Widens the inlet by pulling the aryepiglottic folds apart
Muscles Controlling the Movements of the Vocal Folds (Cords)
Cricothyroid Side of cricoid cartilage Lower border and inferior cornu of thyroid cartilage External laryngeal nerve Tenses vocal cords
Thyroarytenoid (vocalis) Inner surface of thyroid cartilage Arytenoid cartilage Recurrent laryngeal nerve Relaxes vocal cords
Lateral cricoarytenoid Upper border of cricoid cartilage Muscular process of arytenoid cartilage Recurrent laryngeal nerve Adducts the vocal cords by rotating arytenoid cartilage
Posterior cricoarytenoid Back of cricoid cartilage Muscular process of arytenoid cartilage Recurrent laryngeal nerve Abducts the vocal cords by rotating arytenoid cartilage
Transverse arytenoid Back and medial surface of arytenoid cartilage Back and medial surface of opposite arytenoid cartilage Recurrent laryngeal nerve Closes posterior part of rima glottidis by approximating arytenoid cartilages

The rima glottidis is closed by contraction of the lateral cricoarytenoid, which rotates the arytenoid cartilage and adducts the vocal process (Fig. 11-99). The posterior part of the glottis is narrowed when the arytenoid cartilages are drawn together by contraction of the transverse arytenoid muscles. The vocal folds are stretched by contraction of the cricothyroid muscle (Fig. 11-100). The vocal folds are slackened by contraction of the vocalis, a part of the thyroarytenoid muscle (Fig. 11-99). Movements of the Vocal Folds With Respiration On quiet inspiration, the vocal folds are abducted and the rima glottidis is triangular in shape with the apex in front (Fig. 11-99). On expiration the vocal folds are adducted, leaving a small gap between them (Fig. 11-99). On deep inspiration, the vocal folds are maximally abducted and the triangular shape of the glottis becomes a diamond shape because of the maximal lateral rotation of the arytenoid cartilages (Fig. 11-99). Sphincteric Function of the Larynx There are two sphincters in the larynx: one at the inlet and another at the rima glottidis. The sphincter at the inlet is used only during swallowing. As the bolus of food is passed backward between the tongue and the hard palate, the larynx is pulled up beneath the back of the tongue. The inlet of the larynx is narrowed by the action of the oblique arytenoid and aryepiglottic muscles. The epiglottis is pulled backward by the tongue and serves as a cap over the laryngeal inlet. The bolus of food, or fluids, then enters the esophagus by passing over the epiglottis or moving down the grooves on either side of the laryngeal inlet, the piriform fossae. In coughing or sneezing, the rima glottidis serves as a sphincter. After inspiration, the vocal folds are adducted, and the muscles of expiration are made to contract strongly. As a result, the intrathoracic pressure rises, and the vocal folds are suddenly abducted. The sudden release of the compressed air will often dislodge foreign particles or mucus from the respiratory tract and carry the material up into the pharynx, where the material is either swallowed or expectorated. In the Valsalva maneuver, forced expiration takes place against a closed glottis. In abdominal straining associated with micturition, defecation, and parturition, air is often held temporarily in the respiratory tract by closing the rima glottidis. After deep inspiration the rima glottidis is closed. The muscles of the anterior abdominal wall now contract, and the upward movement of the diaphragm is prevented by the presence of compressed air within the respiratory tract. After a prolonged effort the person often releases some of the air by momentarily opening the rima glottidis, producing a grunting sound. Voice Production in the Larynx The intermittent release of expired air between the adducted vocal folds results in their vibration and in the production of sound. The frequency, or pitch, of the sound is determined by changes in the length and tension of the vocal ligaments. The quality of the voice depends on the resonators above the larynx, namely, the pharynx, mouth, and paranasal sinuses. The quality of the voice is controlled by the muscles of the soft plate, tongue, floor of the mouth, cheeks, lips, and jaws. Normal speech depends on the modification of the sound into recognizable consonants and vowels by the use of the tongue, teeth, and lips. Vowel sounds are usually P.807
purely oral with the soft palate raised so that the air is channeled through the mouth rather than the nose.

Figure 11-100 Diagrams showing the attachments and actions of the cricothyroid muscle. A. Right lateral view of the larynx and the cricothyroid muscle. B. Interior view of the larynx showing the relaxed right vocal ligament. C. Interior view of the larynx showing the right vocal ligament stretched as a result of the cricoid and arytenoid cartilages tilting backward by contraction of the cricothyroid muscles.

Speech involves the intermittent release of expired air between the adducted vocal folds. Singing a note requires a more prolonged release of the expired air between the adducted vocal folds. In whispering, the vocal folds are adducted, but the arytenoid cartilages are separated; the vibrations are given to a constant stream of expired air that passes through the posterior part of the rima glottidis. Mucous Membrane of the Larynx The mucous membrane of the larynx lines the cavity and is covered with ciliated columnar epithelium. On the vocal cords, however, where the mucous membrane is subject to repeated trauma during phonation, the mucous membrane is covered with stratified squamous epithelium. Nerve Supply of the Larynx Sensory Nerves

  • Above the vocal cords: The internal laryngeal branch of the superior laryngeal branch of the vagus
  • Below the level of the vocal cords: The recurrent laryngeal nerve (Fig. 11-101)

Motor Nerves All the intrinsic muscles of the larynx except the cricothyroid muscle are supplied by the recurrent laryngeal nerve. The cricothyroid muscle is supplied by the external laryngeal branch of the superior laryngeal branch of the vagus. Blood Supply of the Larynx

  • Upper half of the larynx: The superior laryngeal branch of the superior thyroid artery
  • Lower half of the larynx: The inferior laryngeal branch of the inferior thyroid artery

Lymph Drainage of the Larynx The lymph vessels drain into the deep cervical group of nodes. Clinical Notes Lesions of the Laryngeal Nerves The muscles of the larynx are innervated by the recurrent laryngeal nerves, with the exception of the cricothyroid muscle, which is supplied by the external laryngeal nerve. Both these nerves are vulnerable during operations on the thyroid gland because of the close relationship between them and the arteries of the gland. The left recurrent laryngeal nerve may be involved in a bronchial or esophageal carcinoma or in secondary metastatic deposits in the mediastinal lymph nodes. The right and left recurrent laryngeal nerves may be damaged by malignant involvement of the deep cervical lymph nodes. Section of the external laryngeal nerve produces weakness of the voice because the vocal fold cannot be tensed. The cricothyroid muscle is paralyzed (Fig. 11-102). Unilateral complete section of the recurrent laryngeal nerve results in the vocal fold on the affected side assuming the position midway between abduction and adduction. It lies just lateral to the midline. Speech is not greatly affected because the other vocal fold compensates to some extent and moves toward the affected vocal fold (Fig. 11-102). Bilateral complete section of the recurrent laryngeal nerve results in both vocal folds assuming the position midway between abduction and adduction. Breathing is impaired because the rima glottidis is partially closed, and speech is lost (Fig. 11-102). Unilateral partial section of the recurrent laryngeal nerve results in a greater degree of paralysis of the abductor muscles than of the adductor muscles. The affected vocal fold assumes the adducted midline position (Fig. 11-102). This phenomenon has not been explained satisfactorily. It must be assumed that the abductor muscles receive a greater number of nerves than the adductor muscles, and thus partial damage of the recurrent laryngeal nerve results in damage to relatively more nerve fibers to the abductor muscles. Another possibility is that the nerve fibers to the abductor muscles are traveling in a more exposed position in the recurrent laryngeal nerve and are therefore more prone to be damaged. Bilateral partial section of the recurrent laryngeal nerve results in bilateral paralysis of the abductor muscles and the drawing together of the vocal folds (Fig. 11-102). Acute breathlessness (dyspnea) and stridor follow, and cricothyroidotomy or tracheostomy is necessary. Edema of the Laryngeal Mucous Membrane The mucous membrane of the larynx is loosely attached to the underlying structures by submucous connective tissue. In the region of the vocal folds, however, the mucous membrane is firmly attached to the vocal ligaments. This fact is of clinical importance in cases of edema of the larynx. The accumulation of tissue fluid causes the mucous membrane above the rima glottidis to swell and encroach on the airway. In severe cases, a cricothyroidotomy or tracheostomy may be necessary. Laryngeal Mirror and Laryngoscope The interior of the larynx can be inspected indirectly through a laryngeal mirror passed through the open mouth into the oral pharynx (Fig. 11-103). A more satisfactory method is the direct method using the laryngoscope. The neck is brought forward on a pillow and the head is fully extended at the atlanto-occipital joints. The illuminated instrument can then be introduced into the larynx over the back of the tongue (Fig. 11-103). The valleculae, the piriform fossae, the epiglottis, and the aryepiglottic folds are clearly seen. The two elevations produced by the corniculate and cuneiform cartilages can be recognized. Within the larynx, the vestibular folds and the vocal folds can be seen. The former are fixed, widely separated, and reddish in color; the latter move with respiration and are white in color. With quiet breathing, the rima glottidis is triangular, with the apex in front. With deep inspiration, the rima glottidis assumes a diamond shape because of the lateral rotation of the arytenoid cartilages. If the patient is asked to breathe deeply, the vocal folds become widely abducted, and the inside of the trachea can be seen. Important Anatomic Axes for Endotracheal Intubation The upper airway has three axes that have to be brought into alignment if the glottis is to be viewed adequately through a laryngoscope—the axis of the mouth, the axis of the pharynx, and the axis of the trachea (Fig. 11-104). The following procedures are necessary: First the head is extended at the atlanto-occipital joints. This brings the axis of the mouth into the correct position. Then the neck is flexed at cervical vertebrae C4 to C7 by elevating the back of the head off the table, often with the help of a pillow. This brings the axes of the pharynx and the trachea in line with the axis of the mouth. Anatomy of the Visualization of the Vocal Cords With the Laryngoscope The patient’s head and neck are correctly positioned so that the three axes of the airway (noted above) have been established and the patient has assumed the “sniffing” position. The laryngoscope is inserted into the patient’s mouth, and the blade is correctly placed alongside the right mandibular molar teeth. The blade can then be passed over the tongue and down into the esophagus. The tip of the blade must be fully inserted into the esophagus (so that you know where it is anatomically). The blade should by now have moved toward the midline and followed the anatomic curvature on the posterior surface of the tongue. The laryngoscopic blade is then gently and slowly withdrawn. The tip of the blade is kept under direct vision at all times and is permitted to rise up out of the esophagus. Remember that the tip of the blade is at first in the esophagus and is, therefore, distal to the level of the vocal cords. Once the blade tip has left the esophagus, it is in the laryngeal part of the pharynx (Figs. 11-88 and 11-91), and a view of the glottis should immediately be apparent. This is the critical stage. If the glottis is not visualized, then the operator is viewing the posterior surface of the epiglottis. Now use your anatomic knowledge. With the tip of the blade of the laryngoscope applied to the posterior surface of the epiglottis, gently lift up and elevate the epiglottis to expose the glottis. If the glottis is still not in view, do not panic! Again use your knowledge of anatomy. With the right free hand grasp the thyroid cartilage (to which the cords and the epiglottis are attached) between finger and thumb and apply firm backward, upward, rightward pressure (BURP). This maneuver realigns the box of the larynx relative to the laryngoscopic blade, and the visual axis of the operator and the glottis should immediately be seen. Reflex Activity Secondary to Endotracheal Intubation Stimulation of the mucous membrane of the upper airway during the process of intubation may produce cardiovascular changes such as bradycardia and hypertension. These changes are largely mediated through the branches of the vagus nerves. P.808
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Figure 11-101 A. Lateral view of larynx showing the internal and external laryngeal branches of the superior laryngeal branch of the vagus nerve. B. The distribution of the terminal branches of the internal and recurrent laryngeal nerves. The larynx is viewed from above and posteriorly.
Figure 11-102 The position of the vocal folds (cords) after damage to the external and recurrent laryngeal nerves.

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Figure 11-103 Inspection of the vocal folds (cords) indirectly through a laryngeal mirror (A) and through a laryngoscope (B). Note the orientation of the structures forming the laryngeal inlet.

The Trachea Description The trachea is a mobile cartilaginous and membranous tube (Fig. 11-105). It begins as a continuation of the larynx at the lower border of the cricoid cartilage at the level of the sixth cervical vertebra. It descends in the midline of the neck. In the thorax the trachea ends at the carina by dividing into right and left principal (main) bronchi at the level of the sternal angle (opposite the disc between the fourth and fifth thoracic vertebrae). The fibroelastic tube is kept patent by the presence of U-shaped cartilaginous bar (rings) of hyaline cartilage embedded in its wall. The posterior free ends of the cartilage are connected by smooth muscle, the trachealis muscle. The mucous membrane of the trachea is lined with pseudostratified ciliated columnar epithelium and contains many goblet cells and tubular mucous glands. Relations of the Trachea in the Neck (Fig. 11-49)

  • Anteriorly: Skin, fascia, isthmus of the thyroid gland (in front of the second, third, and fourth rings), inferior P.811
    thyroid vein, jugular arch, thyroidea ima artery (if present), and the left brachiocephalic vein in children, overlapped by the sternothyroid and sternohyoid muscles
    Figure 11-104 Anatomic axes for endotracheal intubation. A. With the head in the neutral position, the axis of the mouth (M), the axis of the trachea (T), and the axis of the pharynx (P) are not aligned with one another. B. If the head is extended at the atlanto-occipital joints, the axis of the mouth is correctly placed. If the back of the head is raised off the table with a pillow, thus flexing the cervical vertebral column, the axes of the trachea and pharynx are brought in line with the axis of the mouth.
  • Posteriorly: Right and left recurrent laryngeal nerves and the esophagus
  • Laterally: Lobes of the thyroid gland and the carotid sheath and contents

The relations of the trachea in the superior mediastinum of the thorax are described on page 87. Nerve Supply of the Trachea The sensory nerve supply is from the vagi and the recurrent laryngeal nerves. Blood Supply of the Trachea The upper two thirds is supplied by the inferior thyroid arteries and the lower third is supplied by the bronchial arteries. Lymph Drainage of the Trachea Into the pretracheal and paratracheal lymph nodes and the deep cervical nodes P.812

Figure 11-105 The trachea and the bronchi.

Clinical Notes Midline Structures in the Neck The midline structures in the neck should be readily recognized as one passes an examining finger down the neck from the chin to the suprasternal notch (for details, see page 839). The physician commonly forgets that an enlarged submental lymph node may be caused by a pathologic condition anywhere between the tip of the tongue and the point of the chin. Palpation of the Trachea The trachea can be readily felt below the larynx. As it descends, it becomes deeply placed and may lie as much as 1.5 in. (4 cm) from the surface at the suprasternal notch. Remember that in the adult it may measure as much as 1 in. (2.5 cm) in diameter, but in a 3-year-old child it may measure only 0.5 in. in diameter. The trachea is a mobile elastic tube and is easily displaced by the enlargement of adjacent organs or the presence of tumors. Remember also that lateral displacement of the cervical part of the trachea may be caused by a pathologic lesion in the thorax. Compromised Airway No medical emergency quite produces the urgency and anxiety of the compromised airway. The physician has to institute almost immediate treatment. All techniques of airway management require a detailed knowledge of anatomy. Cricothyroidotomy In cricothyroidotomy, a tube is inserted in the interval between the cricoid cartilage and the thyroid cartilage. The trachea and larynx are steadied by extending the neck over a sandbag. A vertical or transverse incision is made in the skin in the interval between the cartilages (Fig. 11-106). The incision is made through the following structures: the skin, the superficial fascia (beware of the anterior jugular veins, which lie close together on either side of the midline), the investing layer of deep cervical fascia, the pretracheal fascia (separate the sternohyoid muscles and incise the fascia), and the larynx. The larynx is incised through a horizontal incision through the cricothyroid ligament and the tube inserted. Complications

  • Esophageal perforation: Because the lower end of the pharynx and the beginning of the esophagus lie directly behind the cricoid cartilage, it is imperative that the scalpel incision through the cricothyroid membrane not be carried too far posteriorly. This is particularly important in young children, in whom the cross diameter of the larynx is so small.
  • Hemorrhage: The small branches of the superior thyroid artery that occasionally cross the front of the cricothyroid membrane to anastomose with one another should be avoided.

Tracheostomy Tracheostomy is rarely performed and is limited to patients with extensive laryngeal damage and infants with severe airway obstruction. Because of the presence of major vascular structures (carotid arteries and internal jugular vein), the thyroid gland, nerves (recurrent laryngeal branch of vagus and vagus nerve), the pleural cavities, and the esophagus, meticulous attention to anatomic detail has to be observed (Fig. 11-107). The procedure is as follows:

  • The thyroid and cricoid cartilages are identified and the neck is extended to bring the trachea forward.
  • A vertical midline skin incision is made from the region of the cricothyroid membrane inferiorly toward the suprasternal notch.
  • The incision is carried through the superficial fascia and the fibers of the platysma muscle. The anterior jugular veins in the superficial fascia are avoided by maintaining a midline position.
  • The investing layer of deep cervical fascia is incised.
  • The pretracheal muscles embedded in the pretracheal fascia are split in the midline two fingerbreadths superior to the sternal notch.
  • The tracheal rings are then palpable in the midline or the isthmus of the thyroid gland is visible. If a hook is placed under the lower border of the cricoid cartilage and traction is applied upward, the slack is taken out of the elastic trachea; this stops it from slipping from side to side.
  • A decision is then made as to whether to enter the trachea through the second ring above the isthmus of the thyroid gland; through the third, fourth, or fifth ring by first dividing the vascular isthmus of the thyroid gland; or through the lower tracheal rings below the thyroid isthmus. At the latter site, the trachea is receding from the surface of the neck, and the pretracheal fascia contains the inferior thyroid veins and possibly the thyroidea ima artery.
  • The preferred site is through the second ring of the trachea in the midline, with the thyroid isthmus retracted inferiorly. A vertical tracheal incision is made, and the tracheostomy tube is inserted.

Complications Most complications result from not adequately palpating and recognizing the thyroid, cricoid, and tracheal cartilages and not confining the incision strictly to the midline.

  • Hemorrhage: The anterior jugular veins located in the superficial fascia close to the midline should be avoided. If the isthmus of the thyroid gland is transected, secure the anastomosing branches of the superior and inferior thyroid arteries that cross the midline on the isthmus.
  • Nerve paralysis: The recurrent laryngeal nerves may be damaged as they ascend the neck in the groove between the trachea and the esophagus.
  • Pneumothorax: The cervical dome of the pleura may be pierced. This is especially common in children because of the high level of the pleura in the neck.
  • Esophageal injury: Damage to the esophagus, which is located immediately posterior to the trachea, occurs most commonly in infants; it follows penetration of the small-diameter trachea by the point of the scalpel blade.

Some Important Airway Distances Table 11-13 shows some important distances between the incisor teeth or nostrils to anatomic landmarks in the airway in the adult. These approximate figures are helpful in determining the correct placement of an endotracheal tube (see page 808). P.813

Figure 11-106 The anatomy of cricothyroidotomy. A. A vertical incision is made through the skin and superficial and deep cervical fasciae. B. The cricothyroid membrane (ligament) is incised through a horizontal incision close to the upper border of the cricoid cartilage. C. Insertion of the tube.

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Figure 11-107 Cross section of the neck at the level of the second tracheal ring. A vertical incision is made through the ring, and the tracheostomy tube is inserted.
Table 11-13 Important Airway Distances (Adult)a
Airway Distances
Incisor teeth to the vocal cords 5.9 in. (15 cm)
Incisor teeth to the carina 7.9 in. (20 cm)
External nares to the carina 11.8 in. (30 cm)
aAverage figures given = 1–2 cm.

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Endocrine Glands in the Head and Neck Pituitary Gland (Hypophysis Cerebri) Location and Description The pituitary gland is a small, oval structure attached to the undersurface of the brain by the infundibulum (Figs. 11-13 and 11-108). The gland is well protected by virtue of its location in the sella turcica of the sphenoid bone. Because the hormones produced by the gland influence the activities of many other endocrine glands, the hypophysis cerebri is often referred to as the master endocrine gland. For this reason, it is vital to life. The pituitary gland is divided into an anterior lobe, or adenohypophysis, and a posterior lobe, or neurohypophysis. The anterior lobe is subdivided into the pars anterior (sometimes called the pars distalis) and the pars intermedia, which may be separated by a cleft that is a remnant of an embryonic pouch. A projection from the pars anterior, the pars tuberalis, extends up along the anterior and lateral surfaces of the pituitary stalk. Relations

  • Anteriorly: The sphenoid sinus (Fig. 11-13)
  • Posteriorly: The dorsum sellae, the basilar artery, and the pons
  • Superiorly: The diaphragma sellae, which has a central aperture that allows the passage of the infundibulum. The diaphragma sellae separates the anterior lobe from the optic chiasma (Fig. 11-108).
  • Inferiorly: The body of the sphenoid, with its sphenoid air sinuses
  • Laterally: The cavernous sinus and its contents (Fig. 11-108)

Blood Supply The arteries are derived from the superior and inferior hypophyseal arteries, branches of the internal carotid artery. The veins drain into the intercavernous sinuses. Functions of the Pituitary Gland The pituitary gland influences the activities of many other endocrine glands. The pituitary gland is itself controlled by the hypothalamus and the activities of the hypothalamus are modified by information received along numerous nervous afferent pathways from different parts of the central nervous system and by the plasma levels of the circulating electrolytes and hormones.]

Figure 11-108 Coronal section through the body of the sphenoid bone, showing the pituitary gland and cavernous sinuses. Note the position of the internal carotid artery and the cranial nerves.

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Embryologic Notes Development of the Pituitary Gland The pituitary gland develops from two sources: a small ectodermal diverticulum (Rathke’s pouch), which grows superiorly from the roof of the stomodeum immediately anterior to the buccopharyngeal membrane, and a small ectodermal diverticulum (the infundibulum), which grows inferiorly from the floor of the diencephalon of the brain (Fig. 11-109). During the second month of development, Rathke’s pouch comes into contact with the anterior surface of the infundibulum, and its connection with the oral epithelium elongates, narrows, and finally disappears (Fig. 11-109). Rathke’s pouch now is a vesicle that flattens itself around the anterior and lateral surfaces of the infundibulum. The cells of the anterior wall of the vesicle proliferate and form the pars anterior of the pituitary; from the vesicle’s upper part, there is a cellular extension that grows superiorly and around the stalk of the infundibulum, forming the pars tuberalis. The cells of the posterior wall of the vesicle never develop extensively; they form the pars intermedia. Some of the cells later migrate anteriorly into the pars anterior. The cavity of the vesicle is reduced to a narrow cleft, which may disappear completely. Meanwhile, the infundibulum has differentiated into the stalk and pars nervosa of the pituitary gland (Fig. 11-109).

Figure 11-109 The different stages in the development of the pituitary gland shown in sagittal sections.

Pineal Gland Location and Description The pineal gland is a small cone-shaped body that projects posteriorly from the posterior end of the roof of the third ventricle of the brain (Fig. 11-13). The pineal consists essentially of groups of cells, the pinealocytes, supported by glial cells. The gland has a rich blood supply and is innervated by postganglionic sympathetic nerve fibers. Functions of the Pineal Gland The pineal gland can influence the activities of the pituitary gland, the islets of Langerhans of the pancreas, the parathyroids, the adrenals, and the gonads. The pineal secretions, produced by the pinealocytes, reach their target organs via the bloodstream or through the cerebrospinal fluid. Their actions are mainly inhibitory and either directly inhibit the production of hormones or indirectly inhibit the secretion of releasing factors by the hypothalamus. P.817
Thyroid Gland Location and Description The thyroid gland consists of right and left lobes connected by a narrow isthmus (Fig. 11-110). It is a vascular organ surrounded by a sheath derived from the pretracheal layer of deep fascia. The sheath attaches the gland to the larynx and the trachea. Each lobe is pear shaped, with its apex being directed upward as far as the oblique line on the lamina of the thyroid cartilage; its base lies below at the level of the fourth or fifth tracheal ring. The isthmus extends across the midline in front of the second, third, and fourth tracheal rings (Fig. 11-110). A pyramidal lobe is often present, and it projects upward from the isthmus, usually to the left of the midline. A fibrous or P.818
muscular band frequently connects the pyramidal lobe to the hyoid bone; if it is muscular, it is referred to as the levator glandulae thyroideae (Fig. 11-110).

Figure 11-110 The blood supply and venous drainage of the thyroid gland.

Relations of the Lobes

  • Anterolaterally: The sternothyroid, the superior belly of the omohyoid, the sternohyoid, and the anterior border of the sternocleidomastoid (Fig. 11-49)
  • Posterolaterally: The carotid sheath with the common carotid artery, the internal jugular vein, and the vagus nerve (Fig. 11-49)
  • Medially: The larynx, the trachea, the pharynx, and the esophagus. Associated with these structures are the cricothyroid muscle and its nerve supply, the external laryngeal nerve. In the groove between the esophagus and the trachea is the recurrent laryngeal nerve (Fig. 11-49).

The rounded posterior border of each lobe is related posteriorly to the superior and inferior parathyroid glands (Fig. 11-110) and the anastomosis between the superior and inferior thyroid arteries. Relations of the Isthmus

  • Anteriorly: The sternothyroids, sternohyoids, anterior jugular veins, fascia, and skin
  • Posteriorly: The second, third, and fourth rings of the trachea

The terminal branches of the superior thyroid arteries anastomose along its upper border. Blood Supply The arteries to the thyroid gland are the superior thyroid artery, the inferior thyroid artery, and sometimes the thyroidea ima. The arteries anastomose profusely with one another over the surface of the gland. The superior thyroid artery, a branch of the external carotid artery, descends to the upper pole of each lobe, accompanied by the external laryngeal nerve (Fig. 11-110). The inferior thyroid artery, a branch of the thyrocervical trunk, ascends behind the gland to the level of the cricoid cartilage. It then turns medially and downward to reach the posterior border of the gland. The recurrent laryngeal nerve crosses either in front of or behind the artery, or it may pass between its branches. The thyroidea ima, if present, may arise from the brachiocephalic artery or the arch of the aorta. It ascends in front of the trachea to the isthmus (Fig. 11-110). The veins from the thyroid gland are the superior thyroid, which drains into the internal jugular vein; the middle thyroid, which drains into the internal jugular vein; and the inferior thyroid (Fig. 11-110). The inferior thyroid veins of the two sides anastomose with one another as they descend in front of the trachea. They drain into the left brachiocephalic vein in the thorax. Lymph Drainage The lymph from the thyroid gland drains mainly laterally into the deep cervical lymph nodes. A few lymph vessels descend to the paratracheal nodes. Nerve Supply Superior, middle, and inferior cervical sympathetic ganglia Functions of the Thyroid Gland The thyroid hormones, thyroxine and triiodothyronine, increase the metabolic activity of most cells in the body. The parafollicular cells produce the hormone thyrocalcitonin, which lowers the level of blood calcium. Clinical Notes Swellings of the Thyroid Gland and Movement on Swallowing The thyroid gland is invested in a sheath derived from the pretracheal fascia. This tethers the gland to the larynx and the trachea and explains why the thyroid gland follows the movements of the larynx in swallowing. This information is important because any pathologic neck swelling that is part of the thyroid gland will move upward when the patient is asked to swallow. The Thyroid Gland and the Airway The close relationship between the trachea and the lobes of the thyroid gland commonly results in pressure on the trachea in patients with pathologic enlargement of the thyroid. Retrosternal Goiter The attachment of the sternothyroid muscles to the thyroid cartilage effectively binds down the thyroid gland to the larynx and limits upward expansion of the gland. There being no limitation to downward expansion, it is not uncommon for a pathologically enlarged thyroid gland to extend downward behind the sternum. A retrosternal goiter (any abnormal enlargement of the thyroid gland) can compress the trachea and cause dangerous dyspnea; it can also cause severe venous compression. Thyroid Arteries and Important Nerves It should be remembered that the two main arteries supplying the thyroid gland are closely related to important nerves that can be damaged during thyroidectomy operations. The superior thyroid artery on each side is related to the external laryngeal nerve, which supplies the cricothyroid muscle. The terminal branches of the inferior thyroid artery on each side are related to the recurrent laryngeal nerve. Damage to the external laryngeal nerve results in an inability to tense the vocal folds and in hoarseness. For the results of damage to the recurrent laryngeal nerve, see page 808. Thyroidectomy and the Parathyroid Glands The parathyroid glands are usually four in number and are closely related to the posterior surface of the thyroid gland. In partial thyroidectomy, the posterior part of the thyroid gland is left undisturbed so that the parathyroid glands are not damaged. The development of the inferior parathyroid glands is closely associated with the thymus. For this reason it is not uncommon for the surgeon to find the inferior parathyroid glands in the superior mediastinum because they have been pulled down into the thorax by the thymus. P.819
Embryologic Notes Development of the Thyroid Gland The thyroid gland begins to develop during the third week as an entodermal thickening in the midline of the floor of the pharynx between the tuberculum impar and the copula (Fig. 11-111). Later, this thickening becomes a diverticulum that grows inferiorly into the underlying mesenchyme and is called the thyroglossal duct. As development continues, the duct elongates, and its distal end becomes bilobed. Soon, the duct becomes a solid cord of cells, and as a result of epithelial proliferation, the bilobed terminal swellings expand to form the thyroid gland. The thyroid gland now migrates inferiorly in the neck and passes either anterior to, posterior to, or through the developing body of the hyoid bone. By the seventh week, it reaches its final position in relation to the larynx and trachea. Meanwhile, the solid cord connecting the thyroid gland to the tongue fragments and disappears. The site of origin of the thyroglossal duct on the tongue remains as a pit called the foramen cecum. The thyroid gland may now be divided into a small median isthmus and two large lateral lobes (Fig. 11-111). In the earliest stages, the thyroid gland consists of a solid mass of cells. Later, as a result of invasion by surrounding vascular mesenchymal tissue, the mass becomes broken up into plates and cords and finally into small clusters of cells. By the third month, colloid starts to accumulate in the center of each cluster so that follicles are formed. The fibrous capsule and connective tissue develop from the surrounding mesenchyme. The ultimobranchial bodies (from the fifth pharyngeal pouch) and neural crest cells are believed to be incorporated into the thyroid gland, where they form the parafollicular cells, which produce calcitonin. Agenesis of the Thyroid Failure of development of the thyroid gland may occur and is the commonest cause of cretinism. Incomplete Descent of the Thyroid The descent of the thyroid may be arrested at any point between the base of the tongue and the trachea (Fig. 11-112). Lingual thyroid is the most common form of incomplete descent (Fig. 11-113). The mass of tissue found just beneath the foramen cecum may be sufficiently large to obstruct swallowing in the infant. Ectopic Thyroid Tissue Ectopic thyroid tissue is occasionally found in the thorax in relation to the trachea or bronchi or even the esophagus. It is assumed that this thyroid tissue arises from entodermal cells displaced during the formation of the laryngotracheal tube or from entodermal cells of the developing esophagus Persistent Thyroglossal Duct Conditions related to a persistence of the thyroglossal duct usually appear in childhood, in adolescence, or in young adults. Thyroglossal Cyst Cysts may occur at any point along the thyroglossal tract (Figs. 11-112 and 11-114). They occur most commonly in the region below the hyoid bone. Such a cyst occupies the midline and develops as a result of persistence of a small amount of epithelium that continues to secrete mucus. As the cyst enlarges, it is prone to infection and so it should be removed surgically. Since remnants of the duct often traverse the body of the hyoid bone, this may have to be excised also to prevent recurrence. Thyroglossal Sinus (Fistula) Occasionally, a thyroglossal cyst ruptures spontaneously, producing a sinus (Fig. 11-112). Usually, this is a result of an infection of a cyst. All remnants of the thyroglossal duct should be removed surgically. P.820

Figure 11-111 The different stages in the development of the thyroid gland. A. Sagittal section of the tongue showing an entodermal thickening between the tuberculum impar and the copula. B. Sagittal section of the tongue showing the development of the thyroglossal duct. C. Sagittal section of the tongue and neck showing the path taken by the thyroid gland as it migrates inferiorly. D. The fully developed thyroid gland as seen from in front. Note the remains of the thyroglossal duct above the isthmus.
Figure 11-112 A thyroglossal cyst in the midline in the neck and a thyroglossal fistula.
Figure 11-113 Lingual thyroid. (Courtesy of J. Randolph.)

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Figure 11-114 A thyroglossal cyst. (Courtesy of L. Thompson.)

Parathyroid Glands Location and Description The parathyroid glands are ovoid bodies measuring about 6 mm long in their greatest diameter. They are four in number and are closely related to the posterior border of the thyroid gland, lying within its fascial capsule (Fig. 11-110). The two superior parathyroid glands are the more constant in position and lie at the level of the middle of the posterior border of the thyroid gland. The two inferior parathyroid glands usually lie close to the inferior poles of the thyroid gland. They may lie within the fascial sheath, embedded in the thyroid substance, or outside the fascial sheath. Sometimes they are found some distance caudal to the thyroid gland, in association with the inferior thyroid veins, or they may even reside in the superior mediastinum in the thorax. Blood Supply The arterial supply to the parathyroid glands is from the superior and inferior thyroid arteries. The venous drainage is into the superior, middle, and inferior thyroid veins. Lymph Drainage Deep cervical and paratracheal lymph nodes Nerve Supply Superior or middle cervical sympathetic ganglia Functions of the Parathyroid Glands The chief cells produce the parathyroid hormone, which stimulates osteoclastic activity in bones, thus mobilizing the bone calcium and increasing the calcium levels in the blood. The parathyroid hormone also stimulates the absorption of dietary calcium from the small intestine and the reabsorption of calcium in the proximal convoluted tubules of the kidney. It also strongly diminishes the reabsorption of phosphate in the proximal convoluted tubules of the kidney. The secretion of the parathyroid hormone is controlled by the calcium levels in the blood. The Root of the Neck The root of the neck can be defined as the area of the neck immediately above the inlet into the thorax (Fig. 11-16). Embryologic Notes Development of the Parathyroid Glands The pair of inferior parathyroid glands, known as parathyroid III, develop as the result of proliferation of entodermal cells in the third pharyngeal pouch on each side. As the thymic diverticulum on each side grows inferiorly in the neck, it pulls the inferior parathyroid with it, so that it finally comes to rest on the posterior surface of the lateral lobe of the thyroid gland near its lower pole and becomes completely separate from the thymus (Fig. 11-115). The pair of superior parathyroid glands, parathyroid IV, develop as a proliferation of entodermal cells in the fourth pharyngeal pouch on each side. These loosen their connection with the pharyngeal wall and take up their final position on the posterior aspect of the lateral lobe of the thyroid gland on each side, at about the level of the isthmus (Fig. 11-115). In the earliest stages, each gland consists of a solid mass of clear cells, the chief cells. In late childhood, acidophilic cells, the oxyphil cells, appear. The connective tissue and vascular supply are derived from the surrounding mesenchyme. It is believed that the parathyroid hormone is secreted early in fetal life by the chief cells, to regulate calcium metabolism. The oxyphil cells are thought to be nonfunctioning chief cells. Absence and Hypoplasia of the Parathyroid Glands Agenesis or incomplete development of the parathyroid glands has been demonstrated in individuals with idiopathic hypoparathyroidism. Ectopic Parathyroid Glands The close relationship between the parathyroid III and the developing thymus explains the frequent finding of parathyroid tissue in the superior mediastinum of the thorax (Fig. 11-115). If the parathyroid glands remain attached to the thymus, they may be pulled inferiorly into the lower part of the neck or thoracic cavity. Moreover, this also explains the variable position of the inferior parathyroid glands in relation to the lower poles of the lateral lobes of the thyroid gland. P.822

Figure 11-115 Parathyroid glands taking up their final positions in the neck.

Muscles of the Root of the Neck Scalenus Anterior The scalenus anterior muscle (Fig. 11-57) is a key muscle to the understanding of the root of the neck and has been fully described on page 743. It is deeply placed and descends almost vertically from the vertebral column to the first rib. Because the muscle is an important landmark in the neck, its relations should be understood. see page 743. Scalenus Medius The scalenus medius lies behind the scalenus anterior and extends from the transverse process of the atlas and the transverse processes of the next five cervical vertebrae (Fig. 11-57) downward and laterally to be inserted into the upper surface of the first rib behind the groove for the subclavian artery. The muscle lies behind the roots of the brachial plexus and the subclavian artery. For a summary of muscles of the neck, their nerve supply, and their action, see Table 11-5. Subclavian Artery The right subclavian artery arises from the brachiocephalic artery, behind the right sternoclavicular joint (Fig. 11-57). It passes upward and laterally as a gentle curve behind the scalenus anterior muscle, and at the outer border of the first rib it becomes the axillary artery. The left subclavian artery arises from the arch of the aorta in the thorax. It ascends to the root of the neck and then arches laterally in a manner similar to that of the right subclavian artery (Fig. 11-57). The relations and branches of the subclavian arteries have been described on page 751. P.823

Figure 11-116 A. Cross section of the head a short distance beneath the vault of the skull viewed from below. B. Cross section of the head at the level of the corpus callosum viewed from below.

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Subclavian Vein The subclavian vein begins at the outer border of the first rib as a continuation of the axillary vein (Fig. 11-57). At the medial border of the scalenus anterior it joins the internal jugular vein to form the brachiocephalic vein. The Thoracic Duct The thoracic duct begins in the abdomen at the upper end of the cisterna chyli (see page 273). It enters the thorax through the aortic opening in the diaphragm and ascends through the posterior mediastinum, inclining gradually to the left. On reaching the superior mediastinum, it is found passing upward along the left margin of the esophagus. At the root of the neck, it continues to ascend along the left margin of the esophagus until it reaches the level of the transverse process of the seventh cervical vertebra. Here, it bends laterally behind the carotid sheath (Fig. 11-57). On reaching the medial border of the scalenus anterior, it turns downward and drains into the beginning of the left brachiocephalic vein. It may, however, end in the terminal part of the subclavian or internal jugular veins. Clinical Notes Pleura and Lung Injuries in the Root of the Neck The cervical dome of the pleura and the apex of the lung extend up into the root of the neck on each side. Covered by the suprapleural membrane, they lie behind the subclavian artery. A penetrating wound above the medial end of the clavicle may involve the apex of the lung. Radiographic Anatomy Before studying the radiographic appearance of the head and neck, the student is encouraged to examine photographs of sections of the head and neck (Figs. 11-116, 11-117, and 11-118). Radiographic Appearance of the Head and Neck Routine radiologic examination of the head and neck concentrates mainly on the bony structures because the brain, muscles, tendons, and nerves blend into a homogeneous mass. However, a few normal structures within the skull become calcified in the adult, and the displacement of such structures may indirectly give evidence of a pathologic condition. The pineal gland, for example, is calcified in 50% of normal adults. It lies in the midline. The falx cerebri and the choroid plexuses also become calcified frequently. The brain can be studied indirectly by the injection of contrast media into the arterial system leading to the brain (cerebral arteriogram). The introduction of CT and MRI scans has provided physicians with safe and accurate methods of studying the intracranial contents. Radiographic Appearance of the Skull The radiographic appearances of the skull as seen on straight posteroanterior views and lateral views can be studied in Figures 11-119, 11-120, 11-121, and 11-122. Cerebral Arteriography The technique of cerebral arteriography can be used to detect abnormalities of the cerebral arteries and localization of space-occupying lesions such as tumors, blood clots, or abscesses. Examples of cerebral arteriograms can be seen in Figures 11-123, 11-124, 11-125, and 11-126. Computed Tomography Scans CT is commonly used for the detection of intracranial lesions. It is safe and provides accurate information. Examples of CT scans of the head can be seen in Figure 11-127. Magnetic Resonance Imaging MRI is also commonly used for detection of intracranial lesions. MRI is absolutely safe to the patient, and because it provides better differentiation between gray and white matter in the brain, its use can be more revealing than a CT scan (Figs. 11-128, 11-129, and 11-130). Surface Anatomy Surface Landmarks of the Head Nasion The nasion is the depression in the midline at the root of the nose (Fig. 11-131). External Occipital Protuberance This is a bony prominence in the middle of the squamous part of the occipital bone (Fig. 11-131). It lies in the midline at the junction of the head and neck and gives attachment to the ligamentum nuchae, which is a large ligament that runs down the back of the neck, connecting the skull to the spinous processes of the cervical vertebrae. A line joining the nasion to the external occipital protuberance over the superior aspect of the head would indicate the position of the underlying falx cerebri, the superior sagittal sinus, and the longitudinal cerebral fissure, which separates the right and left cerebral hemispheres. Vertex The vertex is the highest point on the skull in the sagittal plane (Fig. 11-131). Anterior Fontanelle In the baby, the anterior fontanelle lies between the two halves of the frontal bone in front and the two parietal bones behind (Fig. 11-131). It is usually not palpable after 18 months. P.825

Figure 11-117 A. Cross section of the head viewed from below. B. Coronal section of the head and the upper part of the neck.

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Figure 11-118 A. Cross section of the head just below the level of the hard palate viewed from below. B. Cross section of the neck at the level of the sixth cervical vertebra viewed from below.

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Figure 11-119 Posteroanterior radiograph of the skull.

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Figure 11-120 Main features that can be seen in the posteroanterior radiograph of the skull in Figure 11-119.

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Figure 11-121 Lateral radiograph of the skull.

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Figure 11-122 Main features that can be seen in the lateral radiograph of the skull in Figure 11-121.
Figure 11-123 Lateral internal carotid arteriogram.

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Figure 11-124 Main features that can be seen in the arteriogram in Figure 11-123.

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Figure 11-125 Anteroposterior internal carotid arteriogram.

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Figure 11-126 Main features that can be seen in the arteriogram in Figure 11-125.

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Figure 11-127 Axial (horizontal) computed tomography scans of the skull. A. The skull bones and the brain and the different parts of the lateral ventricles. B. A scan made at a lower level showing the three cranial fossae.

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Figure 11-128 Magnetic resonance imaging of the skull. A. Axial image of the brain showing the different parts of the lateral ventricle and the lateral sulcus of the cerebral hemisphere. B. Coronal image through the frontal lobe of the brain showing the anterior horn of the lateral ventricle. Note the improved contrast between the gray and white matter compared with the computed tomography scans seen in Figure 11-127.

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Figure 11-129 Magnetic resonance imaging of the skull. A. Coronal image through the occipital lobes of the brain showing the posterior horn of the lateral ventricle and the cerebellum. B. Sagittal image showing the different parts of the brain and the nasal and mouth cavities.

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Figure 11-130 Axial (horizontal) magnetic resonance imaging showing the contents of the orbital and cranial cavities. Note that the eyeballs, the optic nerves, the optic chiasma, and the extraocular muscles can be identified.

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Posterior Fontanelle In the baby, the posterior fontanelle lies between the squamous part of the occipital bone and the posterior borders of the two parietal bones (Fig. 11-131). It is usually closed by the end of the first year. Superciliary Ridges The superciliary ridges are two prominent ridges on the frontal bones above the upper margin of the orbit (Fig. 11-131). Deep to these ridges on either side of the midline lie the frontal air sinuses. Superior Nuchal Line The superior nuchal line is a curved ridge that runs laterally from the external occipital protuberance to the mastoid process of the temporal bone. It gives attachment to the trapezius and sternocleidomastoid muscles. Mastoid Process of the Temporal Bone The mastoid process projects downward and forward from behind the ear (Figs. 11-131 and 11-134). It is undeveloped in the newborn child and grows only as the result of the pull of the sternocleidomastoid, as the child moves his or her head. It can be recognized as a bony projection at the end of the second year. Auricle and External Auditory Meatus These structures lie in front of the mastoid process (Fig. 11-27). The external auditory meatus is about 1 in. (2.5 cm) long and forms an S-shaped curve. To examine the outer surface of the tympanic membrane in the adult with an otoscope, the tube may be straightened by pulling the auricle upward and backward. In small children, the auricle is pulled straight back or downward and backward. Tympanic Membrane The tympanic membrane is normally pearly gray and is concave toward the meatus (Fig. 11-27). The most depressed part of the concavity is called the umbo and is caused by the attachment of the handle of the malleus on its medial surface. Zygomatic Arch The zygomatic arch extends forward in front of the ear and ends in front in the zygomatic bone (Fig. 11-131). Above the zygomatic arch is the temporal fossa, which is filled with P.839
the temporalis muscle. Attached to the lower margin of the zygomatic arch is the masseter muscle. Contraction of both the temporalis and masseter muscles (Fig. 11-85) can be felt by clenching the teeth.

Figure 11-131 A. Right side of the head showing relations of the middle meningeal artery and the brain to the surface of the skull. B. Superior aspect and right side of the neonatal skull. Note the positions of the anterior and posterior fontanelles.

Superficial Temporal Artery The pulsations of the superficial temporal artery can be felt as it crosses the zygomatic arch, immediately in front of the auricle (Fig. 11-131). Pterion The pterion is the point where the greater wing of the sphenoid meets the anteroinferior angle of the parietal bone. Lying 1.5 in. (4 cm) above the midpoint of the zygomatic arch (Fig. 11-131), it is not marked by an eminence or a depression, but it is important because beneath it lies the anterior branch of the middle meningeal artery. Above and behind the external auditory meatus, deep to the auricle, can be felt a small depression, the suprameatal P.840
triangle (Fig. 11-131). This is bounded behind by a line drawn vertically upward from the posterior margin of the external auditory meatus, above by the suprameatal crest of the temporal bone, and below by the external auditory meatus. The bony floor of the triangle forms the lateral wall of the mastoid antrum. Temporomandibular Joint The temporomandibular joint can be easily palpated in front of the auricle (Fig. 11-131). Note that as the mouth is opened, the head of the mandible rotates and moves forward below the tubercle of the zygomatic arch. Anterior Border of the Ramus of the Mandible The anterior border of the ramus can be felt deep to the masseter muscle. The coronoid process of the mandible can be felt with the gloved finger inside the mouth, and the pterygomandibular ligament can be palpated as a tense band on its medial side. Posterior Border of the Ramus of the Mandible The posterior border of the ramus is overlapped above by the parotid gland (Fig. 11-85), but below it is easily felt through the skin. The outer surface of the ramus of the mandible is covered by the masseter muscle and can be felt on deep palpation when this muscle is relaxed. Body of the Mandible The body of the mandible is best examined by having one finger inside the mouth and another on the outside. Thus, it is possible to examine the mandible from the symphysis menti, in the midline anteriorly, as far backward as the angle of the mandible (Fig. 11-131). Facial Artery The pulsations of the facial artery can be felt as it crosses the lower margin of the body of the mandible, at the anterior border of the masseter muscle (Fig. 11-135). Anterior Border of the Masseter The anterior border of the masseter can be easily felt by clenching the teeth. Parotid Duct The parotid duct runs forward from the parotid gland one fingerbreadth below the zygomatic arch (Fig. 11-135). It can be rolled beneath the examining finger at the anterior border of the masseter as it turns medially and opens into the mouth opposite the upper second molar tooth (Fig. 11-72). Orbital Margin The orbital margin is formed by the frontal, zygomatic, and maxillary bones (Fig. 11-18). Supraorbital Notch If present, the notch can be felt at the junction of the medial and intermediate thirds of the upper margin of the orbit. It transmits the supraorbital nerve, which can be rolled against the bone (Fig. 11-18). Infraorbital Foramen The infraorbital foramen lies 5 mm below the lower margin of the orbit (Fig. 11-1), on a line drawn downward from the supraorbital notch to the interval between the two lower premolar teeth. Infraorbital Nerve The infraorbital nerve emerges from the foramen and supplies the skin of the face. Maxillary Air Sinus The maxillary air sinus is situated within the maxillary bone and lies below the infraorbital foramen on each side (Fig. 11-97). Frontal Air Sinus The frontal air sinus is situated within the frontal bone and lies deep to the superciliary ridge on each side (Fig. 11-97). Surface Landmarks of the Neck Anterior Aspect In the midline anteriorly, the following structures can be palpated from above downward:

  • Symphysis menti: The lower margin can be felt where the two halves of the body of the mandible unite in the midline (Figs. 11-132 and 11-133).
  • Submental triangle: This lies between the symphysis menti and the body of the hyoid bone (Fig. 11-56). It is bounded anteriorly by the midline of the neck, laterally by the anterior belly of the digastric muscle, and inferiorly by the body of the hyoid bone. The floor is formed by the mylohyoid muscle. The submental lymph nodes are located in this triangle.
  • Body of the hyoid bone: This lies opposite the third cervical vertebra (Figs. 11-13 and 11-132).
  • Thyrohyoid membrane: This fills in the interval between the hyoid bone and the thyroid cartilage (Fig. 11-133).
  • Upper border of the thyroid cartilage: This notched structure lies opposite the fourth cervical vertebra (Figs. 11-13 and 11-132).
  • Cricothyroid ligament: This structure fills in the interval between the cricoid cartilage and the thyroid cartilage (Fig. 11-133).
  • Cricoid cartilage: An important landmark in the neck (Fig. 11-132), this lies at the level of the sixth cervical vertebra, at the junction of the larynx with the trachea, at the level of the junction of the pharynx with the esophagus, at the level of the middle cervical sympathetic ganglion, and at the level where the inferior thyroid artery enters the thyroid gland. P.841
    Figure 11-132 Anterior view of the head and neck of a 29-year-old woman. Note that the atlanto-occipital joints and the cervical part of the vertebral column are partially extended for full exposure of the front of the neck.
    Figure 11-133 Surface anatomy of the neck from in front.
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  • Cricotracheal ligament: This structure fills in the interval between the cricoid cartilage and the first ring of the trachea (Fig. 11-98).
  • First ring of the trachea: This can be felt by gentle palpation just above the isthmus of the thyroid gland.
  • Isthmus of the thyroid gland: This lies in front of the second, third, and fourth rings of the trachea (Figs. 11-132 and 11-133).
  • Inferior thyroid veins: The inferior thyroid veins lie in front of the fifth, sixth, and seventh rings of the trachea (Fig. 11-110).
  • Thyroidea ima artery: When present, this artery ascends in front of the trachea to the isthmus of the thyroid gland, from the brachiocephalic artery (Fig. 11-110).
  • Jugular arch: This vein connects the two anterior jugular veins just above the suprasternal notch (Fig. 11-13).
  • Suprasternal notch: This can be felt between the anterior ends of the clavicles (Fig. 11-132). It is the superior border of the manubrium sterni and lies opposite the lower border of the body of the second thoracic vertebra.

In the adult the trachea may measure as much as 1 in. (2.5 cm) in diameter, whereas in a baby it may be narrower than a pencil. In young children, the thymus gland may extend above the suprasternal notch as far as the isthmus of the thyroid gland, and the brachiocephalic artery and the left brachiocephalic vein may protrude above the suprasternal notch. Posterior Aspect In the midline posteriorly, the following structures can be palpated from above downward. The external occipital protuberance lies in the midline at the junction of the head and neck (Fig. 11-135). If the index finger is placed on the skin in the midline, it can be drawn downward in the nuchal groove. The first spinous process to be felt is that of the seventh cervical vertebra (vertebra prominens). Cervical spines one to six are covered by the ligamentum nuchae. Lateral Aspect Sternocleidomastoid Muscle On the side of the neck, the sternocleidomastoid can be palpated throughout its length as it passes upward from the sternum and clavicle to the mastoid process (Figs. 11-134 and 11-135). The muscle can be made to stand out by asking the patient to approximate the ear to the shoulder of the same side and at the same time rotate the head so that the face looks upward toward the opposite side. If the movement is carried out against resistance, the muscle will be felt to contract, and its anterior and posterior borders will be defined. The sternocleidomastoid divides the neck into anterior and posterior triangles. The anterior triangle of the neck is bounded by the body of the mandible, the sternocleidomastoid, and the midline (Fig. 11-56). The posterior triangle is bounded by the anterior border of the trapezius, the sternocleidomastoid, and the clavicle (Fig. 11-56). Trapezius Muscle The anterior border of the trapezius muscle (Fig. 11-132) can be felt by asking the patient to shrug the shoulders. It will be seen to extend from the superior nuchal line of the occipital bone, downward and forward to the posterior border of the lateral third of the clavicle.

Figure 11-134 Anterior view of the neck of a 27-year-old man. Note that the head has been laterally rotated to the left at the atlantoaxial joints and at the joints of the cervical part of the vertebral column.

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Figure 11-135 Surface anatomy of the neck from the lateral aspect.

Platysma Muscle The platysma can be seen as a sheet of muscle by asking the patient to clench the jaws firmly. The muscle extends from the body of the mandible downward over the clavicle onto the anterior thoracic wall (Fig. 11-51). Root of the Neck At the root of the neck are the suprasternal notch in the midline anteriorly (see page 841) and the clavicles. Each clavicle is subcutaneous throughout its entire length and can be easily palpated (Fig. 11-135). It articulates at its lateral extremity with the acromion of the scapula. At the medial end of the clavicle, the sternoclavicular joint can be identified. Anterior Triangle of the Neck The isthmus of the thyroid gland lies in front of the second, third, and fourth rings of the trachea (Figs. 11-132 and 11-133). The lateral lobes of the thyroid gland can be palpated deep to the sternocleidomastoid muscles. This is most easily carried out by standing behind the seated patient and asking the patient to flex the neck forward and so relax the overlying muscles. The observer can then examine both lobes simultaneously with the tips of the fingers of both hands. Carotid Sheath The carotid sheath, which contains the carotid arteries, the internal jugular vein, the vagus nerve, and the deep cervical lymph nodes, can be marked out by a line joining the sternoclavicular joint to a point midway between the tip of the mastoid process and the angle of the mandible. At the level of the upper border of the thyroid cartilage, the common carotid artery bifurcates into the internal and external carotid arteries (Fig. 11-135). The pulsations of these arteries can be felt at this level. P.844
Posterior Triangle of the Neck At the posterior triangle of the neck, the spinal part of the accessory nerve is relatively superficial as it emerges from the posterior border of the sternocleidomastoid and runs downward and backward to pass beneath the anterior border of the trapezius (Fig. 11-135). The course of this nerve may be indicated as follows: Draw a line from the angle of the mandible to the tip of the mastoid process. Bisect this line at right angles and extend the second line downward across the posterior triangle; the second line indicates the course of the nerve. Roots and Trunks of the Brachial Plexus The roots and trunks of the brachial plexus occupy the lower anterior angle of the posterior triangle (Figs. 11-134 and 11-135). The upper limit of the plexus can be indicated by a line drawn from the cricoid cartilage downward to the middle of the clavicle. Third Part of the Subclavian Artery The third part of the subclavian artery also occupies the lower anterior angle of the posterior triangle (Figs. 11-134 and 11-135). Its course may be indicated by a curved line, which passes upward from the sternoclavicular joint for about 0.5 in. (1.3 cm) and then downward to the middle of the clavicle. It is here, where the artery lies on the upper surface of the first rib, that its pulsations can be felt easily. The subclavian vein lies behind the clavicle and does not enter the neck. External Jugular Vein The external jugular vein lies in the superficial fascia deep to the platysma. It passes downward from the region of the angle of the mandible to the middle of the clavicle (Figs. 11-134 and 11-135). It perforates the deep fascia just above the clavicle and drains into the subclavian vein. Salivary Glands The three large salivary glands can be palpated. The parotid gland lies below the ear in the interval between the mandible and the anterior border of the sternocleidomastoid muscle (Fig. 11-85). The surface marking of the parotid duct is given on page 787. The submandibular gland can be divided into superficial and deep parts. The superficial part lies beneath the lower margin of the body of the mandible (Fig. 11-86). The deep part of the submandibular gland, the submandibular duct, and the sublingual gland can be palpated through the mucous membrane covering the floor of the mouth in the interval between the tongue and the lower jaw. The submandibular duct opens into the mouth on the side of the frenulum of the tongue (Fig. 11-72). Clinical Problem Solving Study the following case histories and select the best answer to the questions following them. An 8-year-old girl was taken to a pediatrician because her mother had noticed a small painless swelling below and behind the angle of the jaw on the right side. On examination, the swelling was superficial, cool to touch, and showed no redness. Careful palpation of the neck revealed two firm lumps matted together beneath the anterior border of the right sternocleidomastoid muscle. Examination of the palatine tonsils showed moderate hypertrophy on both sides with a few pustules exuding from the tonsillar crypts on the right side. The patient did not have a pyrexia. 1. The following statements concerning this case are consistent with the patient having chronic cervical lymphadenitis except which? (a) The lymph drains from the tonsil into the superficial cervical lymph nodes, which when enlarged produce a swelling below and behind the angle of the jaw. (b) Tuberculous cervical lymphadenitis is a chronic infection that can enter the tonsil and spread to the lymph nodes. (c) The investing layer of deep cervical fascia can limit the spread of infection in the neck. (d) Tuberculous infection of a lymph node commonly spreads to other nodes in the group and they become matted together. (e) Tuberculous infection results in the destruction of the node with the formation of pus that later erodes through the deep fascia, producing a large cold abscess beneath the skin. (f) Secondary infection of a cold abscess causes the abscess to break through the skin to form a discharging sinus. View Answer1. A. The lymph drains from the tonsil into the jugulodigastric member of the deep cervical lymph nodes. A 25-year-old woman complaining of a swelling on the front of the neck and breathlessness visited her physician. On examination, a small, solitary swelling of firm consistency was found to the left of the midline of the neck below the thyroid cartilage of the larynx. The swelling was not attached to the skin but moved upward on swallowing. About 2 weeks previously the swelling had suddenly increased in size and become tender to touch; following this increase in size the patient became breathless. 2. The following statements concerning this case would suggest a diagnosis of adenoma of the thyroid gland except which? (a) The pretracheal layer of deep cervical fascia binds the thyroid gland to the larynx, which moves upward on swallowing. (b) Each lobe of the thyroid gland is closely related to the sides of the trachea. (c) The isthmus of the thyroid gland was found to cross in front of the third, fourth, and fifth rings of the trachea. (d) The sudden increase in the size of the swelling can be explained by a hemorrhage into the adenoma. (e) The swelling was located superficial to the left sternothyroid muscle. (f) The breathlessness was caused by the adenoma pressing on the trachea, partially occluding the lumen. View Answer2. E. The thyroid gland lies deep to the sternothyroid muscles. A 70-year-old man complaining of a small painless swelling below his chin visited his physician. On questioning, he said that he had first noticed the swelling 4 months earlier and that it was gradually increasing in size. Because it had not caused any discomfort, he had chosen to ignore it. On examination, a single, small, hard swelling could be palpated in the submental triangle. It was mobile on the deep tissues and not attached to the skin. 3. The following statements suggest that the hard swelling was a secondary malignant deposit in a lymph node except which? (a) The submental lymph nodes are located in the submental triangle just below the chin. (b) The submental lymph nodes drain the tip of the tongue, the floor of the mouth in the region of the frenulum of the tongue, the gums and incisor teeth, the middle third of the lower lip, and the skin over the chin. (c) A small, hard-based carcinomatous ulcer was found on the right side of the tongue near the tip. (d) The deep cervical group of lymph nodes beneath the sternocleidomastoid muscle receive lymph from the submental lymph nodes. (e) The submental lymph nodes lie deep to the superficial part of the submandibular salivary gland. View Answer3. E. The submental lymph nodes are not covered by the superficial parts of the submandibular salivary glands. A 45-year-old man with extensive maxillofacial injuries after an automobile accident was brought to the emergency department. Evaluation of the airway revealed partial obstruction. Despite an obvious fractured mandible, an attempt was made to move the tongue forward from the posterior pharyngeal wall by pushing the angles of the mandible forward. This maneuver failed to move the tongue, and it became necessary to hold the tongue forward directly to pull it away from the posterior pharyngeal wall. 4. The most likely reason the physician was unable to pull the tongue forward in this patient is which? (a) The hypoglossal nerves were damaged on both sides of the neck. (b) Spasm of the styloglossus muscles (c) The mandibular origin of the genioglossus muscles was floating because of bilateral fractures of the body of the mandible. (d) The presence of a blood clot in the mouth (e) The resistance of the patient View Answer4. C. The genioglossus muscles arise from the superior mental spines behind the symphysis menti of the mandible. Having passed a laryngoscope into a patient, the anesthetist viewed the following anatomic structures in order from the base of the tongue to the trachea. 5. All the following structures were correctly recognized except which? (a) The median glossoepiglottic fold and the valleculae (b) The two lateral glossoepiglottic folds (c) The upper edge of the epiglottis (d) The aryepiglottic folds (e) The rounded swellings of the cuneiform and corniculate cartilages (f) The mobile vestibular folds (g) The whitish vocal cords (folds) with the rima glottidis View Answer5. F. The vestibular folds of the larynx are fixed and reddish and the vocal folds are mobile and whitish. A 17-year-old boy was seen in the emergency department after receiving a stab wound at the front of the neck. The knife entrance wound was located on the left side of the neck just lateral to the tip of the greater cornu of the hyoid bone. During the physical examination the patient was asked to protrude his tongue, which deviated to the left. 6. The following statements would explain the physical signs in this patient except which? (a) The genioglossus muscles are responsible for protruding the tongue. (b) The genioglossus muscle is supplied by the glossopharyngeal nerve. (c) Paralysis of the left genioglossus muscle permitted the right genioglossus to pull the tongue forward and turned the tip to the left side. (d) The hypoglossal nerve descends in the neck between the internal carotid artery and the internal jugular vein. (e) At about the level of the tip of the greater cornu of the hyoid bone the hypoglossal nerve turns forward and crosses the internal and external carotid arteries and the lingual artery to enter the tongue. (f) The point of the knife blade severed the left hypoglossal nerve. View Answer6. B. The genioglossus muscle is supplied by the hypoglossal nerve. A 43-year-old woman was seen in the emergency department with a large abscess in the middle of the right posterior triangle of the neck. The abscess was red, hot, and fluctuant. The abscess showed evidence that it was pointing and about to rupture. The physician decided to incise the abscess and insert a drain. The patient returned to the department for the dressings to be changed 5 days later. She stated that she felt much better and that her neck was no longer painful. However, there was one thing that she could not understand. She could no longer raise her right hand above her head to brush her hair. 7. The following statements explain the signs and symptoms in this case, suggesting that the spinal part of the accessory nerve had been incised, except which? (a) To raise the hand above the head, it is necessary for the trapezius muscle, assisted by the serratus anterior, to contract and rotate the scapula so that the glenoid cavity faces upward. (b) The trapezius muscle is innervated by the spinal part of the accessory nerve. (c) As the spinal part of the accessory nerve crosses the posterior triangle of the neck, it is deeply placed, being covered by the skin, the superficial fascia, the investing layer of deep cervical fascia, and the levator scapulae muscle. (d) The surface marking of the spinal part of the accessory nerve is as follows: Bisect at right angles a line joining the angle of the jaw to the tip of the mastoid process. Continue the second line downward and backward across the posterior triangle. (e) The knife opening the abscess had cut the accessory nerve. View Answer7. C. The spinal part of the accessory nerve lies superficial to the levator scapulae muscle in the posterior triangle of the neck. A 35-year-old woman had a partial thyroidectomy for the treatment of thyrotoxicosis. During the operation a ligature slipped off the right superior thyroid artery. To stop the hemorrhage, the surgeon blindly grabbed for the artery with artery forceps. The operation was completed without further incident. The following morning the patient spoke with a husky voice. 8. The following statements about this patient would explain the husky voice except which? (a) Laryngoscopic examination revealed that the right vocal cord was slack, causing the huskiness of the voice. (b) The vocal cord is tensed by the contraction of the cricothyroid muscle. (c) The cricothyroid muscle tilts back the cricoid cartilage and pulls forward the thyroid cartilage. (d) The cricothyroid muscle is innervated by the recurrent laryngeal nerve. (e) The superior thyroid artery is closely related to the external laryngeal nerve. View Answer8. D. The cricothyroid muscle is innervated by the external laryngeal nerve, which was damaged in this patient. A 46-year-old man was seen in the emergency department after being knocked down in a street brawl. He had received a blow on the head with an empty bottle. On examination, the patient was conscious and had a large doughlike swelling over the back of the head that was restricted to the area over the occipital bone. The skin was intact, and the swelling fluctuated on palpation. 9. The following statements concerning this patient are correct except which? (a) The hematoma, although large, did not extend forward to the orbital margins and did not extend laterally as far as the temporal lines. (b) The hematoma was located just beneath the epicranial aponeurosis and was superficial to the periosteum of the occipital bone. (c) The swelling did not occupy the subcutaneous tissue of the scalp. (d) The hematoma is restricted to one skull bone and is situated beneath the periosteum. (e) The edge of the swelling is limited by the attachment of the periosteum to the sutural ligaments. View Answer9. B. The hematoma was located deep to the periosteum of the occipital bone. A 17-year-old girl visited her dermatologist because of severe acne of the face. On examination, it was found that a small abscess was present on the side of the nose. The patient was given antibiotics and was warned not to press the abscess. 10. The following facts concerning this patient emphasize why it is important to adequately treat this condition except which? (a) The skin area between the eye, the upper lip, and the side of the nose is a hazardous area to have an infection of the skin. (b) The danger area is drained by the facial vein. (c) Interference with a boil by squeezing or pricking it can lead to spread of the infection and thrombosis of the facial vein. (d) The facial vein communicates with the cavernous sinus via the superior and inferior ophthalmic veins. (e) Cavernous sinus thrombosis can occur by the spread of infection by the venous blood. (f) The blood in the facial vein is unable to spread upward because of valves. View Answer10. F. The facial and ophthalmic veins do not possess valves so that infected blood from the face can spread to the cavernous sinus. A 7-year-old boy with right-sided otitis media was treated with antibiotics. The organisms did not respond to the treatment, and the infection spread to the mastoid antrum and the mastoid air cells. The surgeon decided to perform a radical mastoid operation. After the operation, it was noticed that the boy’s face was distorted. 11. The following signs and symptoms suggest that the right facial nerve had been damaged during the operation except which? (a) The mouth was drawn upward to the right. (b) He was unable to close his right eye. (c) Saliva tended to accumulate in his right cheek. (d) The saliva tended to dribble from the corner of his mouth. (e) All the muscles of the right side of his face were paralyzed. View Answer11. A. The facial muscles on the left side of the mouth on contraction pull the mouth upward and to the left because the muscles on the right side were paralyzed. A 43-year-old woman visited her physician complaining of severe intermittent pain on the right side of her face. The pain was precipitated by exposing the right side of her face to a draft of cold air. The pain was stabbing in nature and lasted about 12 hours before finally disappearing. When asked to point out on her face the area where the pain was experienced, the patient mapped out the skin area over the right side of the lower jaw extending backward and upward over the side of the head to the vertex. 12. The following signs and symptoms in this patient strongly suggest a diagnosis of trigeminal neuralgia except which? (a) The skin area where the patient experienced the pain was innervated by the mandibular division of the trigeminal nerve. (b) The stabbing nature of the pain is characteristic of the disease. (c) The trigger mechanism, stimulation of an area that received its sensory innervation from the trigeminal nerve, is characteristic of trigeminal neuralgia. (d) Examination of the actions of the masseter and the temporalis muscles showed evidence of weakness on the right side. (e) The patient experienced hyperesthesia in the distribution of the right auriculotemporal nerve. View Answer12. D. The motor portion of the trigeminal nerve is unaffected in patients with trigeminal neuralgia. A 10-year-old boy was playing darts with his friends. He bent down to pick up a fallen dart when another dart fell from the dart board and hit him on the side of his face. On examination in the emergency department a small skin wound was found over the right parotid salivary gland. Then 6 months later, the boy’s mother noticed that before mealtimes the boy began to sweat profusely on the facial skin close to the healed dart wound. 13. The following statements can explain this phenomenon except which? (a) The point of the dart had entered the parotid salivary gland and damaged the parasympathetic secretomotor fibers to the gland. (b) The secretomotor fibers to the parotid gland arise in the otic ganglion. (c) The preganglionic parasympathetic fibers originate in the superior salivatory nucleus of the facial nerve. (d) The skin over the parotid salivary gland is innervated by the great auricular nerve, which was also damaged by the dart. (e) On regeneration of the damaged nerves some of the parasympathetic nerves to the parotid salivary gland had crossed over and joined the sympathetic secretomotor nerves to the sweat glands in the distal end of the great auricular nerve. (f) The patient has Frey’s syndrome. View Answer13. C. The secretomotor fibers to the parotid salivary gland originate in the inferior salivatory nucleus of the glossopharyngeal nerve. A 26-year-old baseball player was struck on the right side of the head with a ball. The player fell to the ground but did not lose consciousness. After resting for 1 hour and then getting up, he was seen to be confused and irritable. Later, he staggered and fell to the floor. On questioning, he was seen to be drowsy, and twitching of the lower left half of his face and left arm was noted. 14. A diagnosis of extradural hemorrhage was made based on the following statements except which? (a) A minor blow on the side of the head can easily fracture the thin anteroinferior part of the parietal bone. (b) The posterior branch of the middle meningeal artery may be sectioned at the site of the fracture. (c) Arterial hemorrhage outside the meningeal layer of the dura mater may occur. (d) A large blood clot outside the dura can exert pressure on the lower end of the precentral gyrus. (e) The lower end of the precentral gyrus or motor area supplies the facial muscles and the muscles of the upper limb. View Answer14. B. The anterior branch of the middle meningeal artery may be sectioned at the site of the fracture. A 49-year-old woman was found on ophthalmoscopic examination to have edema of both optic discs (bilateral papilledema) and congestion of both retinal veins. The cause of the condition was found to be a rapidly expanding intracranial tumor. 15. The following statements concerning this patient are correct except which? (a) An intracranial tumor causes a rise in cerebrospinal fluid pressure. (b) The optic nerves are surrounded by sheaths derived from the pia mater, arachnoid mater, and dura mater. (c) The intracranial subarachnoid space extends forward around the optic nerve for about half its length. (d) The thin walls of the retinal vein will be compressed as the vein crosses the extension of the subarachnoid space around the optic nerve. (e) Because both subarachnoid extensions are continuous with the intracranial subarachnoid space, both eyes will exhibit papilledema and congestion of the retinal veins. View Answer15. C. The intracranial subarachnoid space extends forward around the optic nerve as far as the back of the eyeball. A 52-year-old man was eating his dinner in a seafood restaurant when he suddenly choked on a piece of fish. He gasped that he had a bone stuck in his throat. 16. Assuming that the fish bone was stuck in the piriform fossa, the following statements are correct except which? (a) The piriform fossae lie on either side of the entrance into the larynx. (b) The mucous membrane lining the piriform fossae is sensitive and innervated by the recurrent laryngeal nerve. (c) The piriform fossa is bounded laterally by the thyroid cartilage and the thyrohyoid membrane. (d) The piriform fossa is bounded medially by the aryepiglottic fold. (e) The piriform fossa leads inferiorly into the esophagus. View Answer16. B. The mucous membrane lining the piriform fossa is innervated by the internal laryngeal branch of the superior laryngeal nerve from the vagus. P.845
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Review Questions Completion Questions Select the phrase that best completes each statement. 1. The levator palpebrae superioris muscle is innervated by the (a) facial nerve. (b) trochlear nerve. (c) trigeminal nerve. (d) oculomotor nerve. (e) abducent nerve. View Answer1. D. The smooth muscle fibers of the levator palpebrae superioris are innervated by the sympathetic nerves. The greater part of the muscle is made up of striated muscle, which receives its innervation from the oculomotor nerve. Division of the oculomotor nerve causes severe ptosis. 2. The inferior oblique muscle of the eye is innervated by the (a) abducent nerve. (b) trigeminal nerve. (c) oculomotor nerve. (d) facial nerve. (e) trochlear. View Answer2. C 3. The lateral rectus muscle of the eye is innervated by the (a) optic nerve. (b) trochlear nerve. (c) oculomotor nerve. (d) facial nerve. (e) abducent nerve. View Answer3. E 4. The superior oblique muscle of the eye is innervated by the (a) trigeminal nerve. (b) trochlear nerve. (c) abducent nerve. (d) chorda tympani nerve. (e) oculomotor nerve. View Answer4. B 5. The orbicularis oculi muscle is innervated by the (a) facial nerve. (b) lacrimal nerve. (c) maxillary nerve. (d) nasociliary nerve. (e) frontal nerve. View Answer5. A. The orbicularis oculi muscle is a muscle of facial expression. 6. The mandibular division of the trigeminal nerve leaves the skull through the (a) superior orbital fissure. (b) foramen rotundum. (c) foramen ovale. (d) jugular foramen. (e) foramen magnum. View Answer6. C. Both the motor and sensory divisions of the mandibular division of the trigeminal nerve leave the skull together and quickly unite beneath the foramen ovale. 7. The vagus nerve leaves the skull through the (a) jugular foramen. (b) occipital foramen. (c) inferior orbital fissure. (d) foramen rotundum. (e) foramen spinosum. View Answer7. A. The glossopharyngeal, vagus, and accessory (cranial part) nerves leave the skull through the jugular foramen; the sigmoid sinus passes through the posterior part of the same foramen to become the internal jugular vein. 8. The abducent nerve leaves the skull through the (a) foramen rotundum. (b) jugular foramen. (c) inferior orbital fissure. (d) superior orbital fissure. (e) foramen ovale. View Answer8. D 9. The ophthalmic division of the trigeminal nerve leaves the skull through the (a) inferior orbital fissure. (b) foramen ovale. (c) foramen rotundum. (d) superior orbital fissure. (e) pterygopalatine foramen. View Answer9. D. The ophthalmic division of the trigeminal nerve leaves the skull through the superior orbital fissure as its three terminal branches—namely, the lacrimal, frontal, and nasociliary nerves. 10. The maxillary division of the trigeminal nerve leaves the skull through the (a) foramen spinosum. (b) foramen rotundum. (c) superior orbital fissure. (d) foramen ovale. (e) jugular foramen. View Answer10. B 11. The oculomotor nerve leaves the skull through the (a) inferior orbital fissure. (b) foramen rotundum. (c) superior orbital fissure. (d) foramen magnum. (e) foramen ovale. View Answer11. C. The oculomotor nerve passes through the superior orbital fissure as upper and lower divisions. 12. The optic canal is an opening in the (a) lesser wing of the sphenoid bone. (b) occipital bone. (c) petrous part of the temporal bone. (d) frontal bone. (e) squamous part of the temporal bone. View Answer12. A 13. The carotid canal is located in the (a) frontal bone. (b) occipital bone. (c) petrous part of the temporal bone. (d) greater wing of the sphenoid bone. (e) parietal bone. View Answer13. C 14. The foramen spinosum is located in the (a) sphenoid bone. (b) occipital bone. (c) frontal bone. (d) petrous part of the temporal bone. (e) squamous part of the temporal bone. View Answer14. A. The foramen spinosum is located in the greater wing of the sphenoid bone; the middle meningeal artery passes through this foramen into the middle cranial fossa from the infratemporal fossa. 15. The hypoglossal canal is located in the (a) squamous part of the temporal bone. (b) occipital bone. (c) frontal bone. (d) sphenoid bone. (e) parietal bone. View Answer15. B. The hypoglossal canal is situated above the anterolateral boundary of the foramen magnum. 16. The foramen rotundum is located in the (a) lesser wing of the sphenoid bone. (b) frontal bone. (c) petrous part of the temporal bone. (d) occipital bone. (e) greater wing of the sphenoid bone. View Answer16. E. The foramen rotundum transmits the maxillary division of the trigeminal nerve from the middle cranial fossa of the skull into the pterygopalatine fossa. 17. The facial nerve canal is located in the (a) temporal bone. (b) greater wing of the sphenoid bone. (c) occipital bone. (d) mastoid process. (e) lacrimal bone. View Answer17. A 18. The foramen magnum is located in the (a) sphenoid bone. (b) temporal bone. (c) parietal bone. (d) frontal bone. (e) occipital bone. View Answer18. E. The foramen magnum transmits the medulla oblongata, the spinal part of the accessory nerve, and the right and left vertebral arteries. 19. The genioglossus muscle ________ the tongue. (a) retracts (b) depresses (c) elevates (d) protrudes (e) changes the shape of View Answer19. D. Remember that contraction of the right genioglossus muscle (for example) points the tip of the tongue to the patient’s left. 20. The hyoglossus muscle (a) changes the shape of the tongue. (b) elevates the tongue. (c) depresses the tongue. (d) protrudes the tongue. (e) retracts the tongue upward and backward. View Answer20. C 21. The styloglossus muscle (a) protrudes the tongue. (b) depresses the tongue. (c) retracts the tongue upward and backward. (d) changes the shape of the tongue. (e) elevates the tongue. View Answer21. C 22. The palatoglossus muscle (a) depresses the tongue. (b) elevates the tongue. (c) changes the shape of the tongue. (d) retracts the tongue upward and backward. (e) protrudes the tongue. View Answer22. D Multiple-Choice Questions Select the best answer for each question. 23. The following muscles of the pharynx receive their motor innervation from the pharyngeal plexus via the cranial part of the accessory nerve except which? (a) Superior constrictor (b) Palatopharyngeus (c) Stylopharyngeus (d) Middle constrictor (e) Salpingopharyngeus View Answer23. C 24. The following statements concerning the stellate ganglion are correct except which? (a) It is formed from a fusion of the inferior cervical ganglion with the first thoracic ganglion. (b) It has white and gray rami communicantes, which pass to spinal nerves. (c) It is located behind the vertebral artery. (d) It lies in the interval between the transverse process of the seventh cervical vertebra and the neck of the first rib. (e) The large anterior tubercle of the transverse process of the fifth cervical vertebra is an important surface landmark when performing a stellate ganglion block. View Answer24. E. The large anterior tubercle of the transverse process of the sixth cervical vertebra is an important surface landmark when performing a stellate ganglion block. 25. The following statements concerning the chorda tympani are correct except which? (a) It contains parasympathetic postganglionic fibers. (b) It contains special sensory (taste) fibers. (c) It joins the lingual nerve in the infratemporal fossa. (d) It is a branch of the facial nerve in the temporal bone. (e) It carries secretomotor fibers to the submandibular and sublingual salivary glands. View Answer25. A. It contains parasympathetic preganglionic fibers. 26. The following statements concerning the pituitary gland (hypophysis cerebri) are correct except which? (a) It is separated from the optic chiasma by the diaphragma sellae. (b) The sphenoid sinus is inferior to it. (c) It receives its arterial supply from the internal carotid artery. (d) It is suspended from the floor of the third ventricle by the pars anterior. (e) It is deeply placed within the sella turcica of the skull. View Answer26. D. The pituitary is suspended from the floor of the third ventricle by the infundibulum. 27. The following statements concerning the submandibular lymph nodes are correct except which? (a) They drain into the deep cervical lymph nodes. (b) They drain the tip of the tongue. (c) They drain the skin of the forehead. (d) They are situated on the superficial surface of the submandibular salivary gland. (e) They drain the mucous membrane lining the cheek. View Answer27. B. The lymph from the tip of the tongue drains into the submental lymph nodes. 28. The following statements concerning the cervical part of the esophagus are correct except which? (a) The sensory nerve supply is the recurrent laryngeal nerve. (b) The lymph drains into the deep cervical lymph nodes. (c) It is the site of an important portal–systemic anastomosis. (d) The lumen is narrowed at the junction with the pharynx. (e) It begins at the level of the cricoid cartilage, opposite the body of the sixth cervical vertebra. View Answer28. C. The important portal–systemic anastomosis is located in the lower third of the esophagus where it passes through the diaphragm and enters the stomach (see page 245). 29. The following statements concerning the parotid salivary gland are correct except which? (a) The facial nerve passes through it, dividing the gland into superficial and deep parts. (b) The secretomotor nerve supply is derived from the facial nerve. (c) The parotid duct pierces the buccinator muscle and opens into the mouth. (d) The external carotid artery divides within its substance to form the superficial temporal and maxillary arteries. (e) The retromandibular vein is formed within it by the union of the superficial temporal vein and the maxillary vein. View Answer29. B. The secretomotor nerve supply to the parotid salivary gland is from the inferior salivatory nucleus via the glossopharyngeal nerve. 30. The following statements concerning the head and neck are correct except which? (a) The mastoid process of the temporal bone cannot be palpated in the newborn. (b) The deep cervical lymph nodes are situated in the neck along a line that extends from the midpoint between the tip of the mastoid process and the angle of the mandible down to the sternoclavicular joint. (c) The external jugular vein runs down the neck from the angle of the jaw to the middle of the clavicle. (d) The parotid duct opens into the mouth opposite the upper second molar tooth. (e) The anterior fontanelle can be palpated in a baby between the squamous part of the temporal bone, the parietal bone, and the greater wing of the sphenoid. (f) The roots of the brachial plexus emerge into the posterior triangle on the neck between the scalenus anterior and scalenus medius muscles. View Answer30. E 31. The following facts concerning the tongue are correct except which? (a) The intrinsic muscles of the tongue are innervated by the hypoglossal nerve. (b) The taste buds of the vallate papillae are innervated by the glossopharyngeal nerve. (c) The posterior third of the tongue forms part of the anterior wall of the oral pharynx. (d) Lymphoid tissue is found on the anterior third of the dorsum of the tongue. (e) On either side of the frenulum of the tongue are situated the openings of the submandibular ducts. View Answer31. D. The lymphoid tissue is found on the dorsum of the posterior third of the tongue (lingual tonsil) where it forms part of the ring of lymphoid tissue guarding the entrance into the pharynx. 32. Which of the following muscles elevates the soft palate during swallowing? (a) Tensor veli palatini (b) Palatoglossus (c) Palatopharyngeus (d) Levator veli palatini (e) Salpingopharyngeus View Answer32. D 33. Which of the following muscles partially inserts on the articular disc of the temporomandibular joint? (a) Medial pterygoid (b) Anterior fibers of the temporalis (c) Masseter (d) Posterior fibers of the temporalis (e) Lateral pterygoid View Answer33. E 34. Assuming that the patient’s eyesight is normal, in which cranial nerve is there likely to be a lesion when the direct and consensual light reflexes are absent? (a) Trochlear nerve (b) Optic nerve (c) Abducent nerve (d) Oculomotor nerve (e) Trigeminal nerve View Answer34. D 35. A patient is unable to taste a piece of sugar placed on the anterior part of the tongue. Which cranial nerve is likely to have a lesion? (a) Hypoglossal (b) Vagus (c) Glossopharyngeal (d) Facial (e) Maxillary division of the trigeminal View Answer35. D 36. On asking a patient to say “ah,” the uvula is seen to be drawn upward to the right. Which cranial nerve is likely to be damaged? (a) Left glossopharyngeal (b) Right hypoglossal (c) Left accessory (cranial part) (d) Right vagus (e) Right trigeminal View Answer36. C 37. When testing the sensory innervation of the face, it is important to remember that the skin of the tip of the nose is supplied by which one of the following nerves? (a) Zygomatic branch of the facial nerve (b) Maxillary division of the trigeminal nerve (c) Ophthalmic division of the trigeminal nerve (d) External nasal branch of the facial nerve (e) Buccal branch of the mandibular division of the trigeminal nerve View Answer37. C. The external nasal nerve is a continuation of the anterior ethmoidal branch of the nasociliary branch of the ophthalmic division of the trigeminal nerve. Read the case histories and select the best answer to the question following them. An 18-year-old woman went to her physician because she had noticed a swelling in the midline of her neck. She said she had first noticed this swelling 3 years previously, and it had gradually increased in size. On physical examination, a small swelling was found in the midline of the neck; it measured about 0.5 in. (1.25 cm) in diameter. It was situated just below the body of the hyoid bone, was soft and fluctuant, and moved upward on swallowing. Nothing else abnormal was discovered. 38. The physician made the diagnosis of thyroglossal cyst based on the following symptoms and signs except which? (a) The swelling was not hard. (b) The swelling was fluctuant. (c) The swelling was located in the midline of the neck. (d) It moved upward on swallowing, which indicated that it was tethered to tissue associated with the thyroid gland. (e) A thyroglossal cyst is always found below the hyoid bone. View Answer38. E. A thyroglossal cyst occurs most commonly in the midline of the neck below the hyoid bone and above the isthmus of the thyroid gland. It should be emphasized that it can occur anywhere along the path of the thyroglossal tract, even as far superiorly as the foramen cecum of the tongue. As the cyst enlarges it is prone to infection so it should be removed surgically. A 4-week-old baby boy was examined by a pediatrician because of failure to gain weight and difficulty with feeding. The mother said that the child was breast-fed and eagerly accepted the milk when it was manually expressed from the breast, but obviously was having difficulty in sucking at the nipple. The physician carefully examined the baby and then made a diagnosis and advised appropriate treatment. 39. The following statements about this case are correct except which? (a) The condition is often associated with a cleft upper lip. (b) The baby had a median cleft palate. (c) The cleft in the palate involved the hard palate but not the soft palate or the uvula. (d) The difficulty with the feeding was that the cleft palate prevented the child from actively sucking milk from the breast. (e) Surgical repair of a cleft palate should be undertaken at or before 18 months. View Answer39. C. During development the palatal processes of the maxilla grow medially and fuse with each other and the nasal septum; the fusion of the processes takes place from anterior to posterior so that the uvula is the last part of the palate to fuse, and this occurs at about the 11th week. If the pediatrician had made a more thorough examination in a good light, he or she would have seen that the cleft in the hard palate extended all the way posteriorly to the tip of the uvula. Surgical repair of a cleft palate must be undertaken before the child starts to speak. In the meantime, the child should be fed with the mother’s milk with a pipette or spoon, after careful manual expression. Because of the risk of aspiration pneumonia, great care must be taken to prevent the milk from pouring down the throat into the larynx. P.848
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