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Chapter 8The Perineum A 51-year-old woman was seen by her physician for complaints of breathlessness, which she noticed was worse on climbing stairs. On questioning, she said that the problem started about 3 years ago and was getting worse. On examination, the patient was found to have a healthy appearance, although the conjunctivae and lips were paler than normal, suggesting anemia. The cardiovascular and respiratory systems were normal. On further questioning, the patient said that she frequently passed blood-stained stools and was often constipated. Digital examination of the anal canal revealed nothing abnormal apart from the presence of some blood-stained mucus on the glove. Proctoscopic examination revealed that the mucous membrane of the anal canal had three congested swellings that bulged into the lumen at the 3-, 7-, and 11-o’clock positions (the patient was in the lithotomy position). Laboratory examination of the blood showed the red blood cells to be smaller than normal, and the red blood cell count was very low; the hemoglobin level was also low. The diagnosis was microcytic hypochromic anemia, secondary to prolonged bleeding from internal hemorrhoids. The severe anemia explained the patient’s breathlessness. The hemorrhoids were dilatations of the tributaries of the superior rectal vein in the wall of the anal canal. Repeated abrasion of the hemorrhoids by hard stools caused the bleeding and loss of blood. Without knowledge of the anatomic position of the veins in the anal canal, the physician would not have been able to make a diagnosis. P.388
Chapter Objectives

  • Infections, injuries, and prolapses involving the anal canal, the urethra, and the female external genitalia are common problems facing the physician.
  • Urethral obstruction, traumatic rupture of the penile urethra, and infections of the epididymis and testis are frequently seen in the male.
  • The purpose of this chapter is to cover the significant anatomy relative to these clinical problems. Because the descent of the testes and the structure of the scrotum are intimately related to the development of the inguinal canal, they are dealt with in detail in Chapter 4.

Basic Anatomy Definition of Perineum The cavity of the pelvis is divided by the pelvic diaphragm into the main pelvic cavity above and the perineum below (Fig. 8-1). When seen from below with the thighs abducted, the perineum is diamond shaped and is bounded anteriorly by the symphysis pubis, posteriorly by the tip of the coccyx, and laterally by the ischial tuberosities (Fig. 8-2). Pelvic Diaphragm The pelvic diaphragm is formed by the important levatores ani muscles and the small coccygeus muscles and their covering fasciae (Fig. 8-1). It is incomplete anteriorly to allow passage of the urethra in males and the urethra and the vagina in females (for details see page 318). Contents of Anal Triangle The anal triangle is bounded behind by the tip of the coccyx and on each side by the ischial tuberosity and the sacrotuberous ligament, overlapped by the border of the gluteus maximus muscle (Fig. 8-3). The anus, or lower opening of the anal canal, lies in the midline, and on each side is the ischiorectal fossa. The skin around the anus is supplied by the inferior rectal (hemorrhoidal) nerve. The lymph vessels of the skin drain into the medial group of the superficial inguinal nodes. Anal Canal Location and Description The anal canal is about 1.5 in. (4 cm) long and passes downward and backward from the rectal ampulla to the anus (Fig. 8-4). Except during defecation, its lateral walls are kept in apposition by the levatores ani muscles and the anal sphincters. Relations

  • Posteriorly: The anococcygeal body, which is a mass of fibrous tissue lying between the anal canal and the coccyx (Fig. 8-4)
  • Laterally: The fat-filled ischiorectal fossae (Fig. 8-5)
  • Anteriorly: In the male, the perineal body, the urogenital diaphragm, the membranous part of the urethra, and P.389
    the bulb of the penis (Fig. 8-4). In the female, the perineal body, the urogenital diaphragm, and the lower part of the vagina (Fig. 8-4).
Figure 8-1 Right half of the pelvis showing the muscles forming the pelvic floor. Note that the levator ani and coccygeus muscles and their covering fascia form the pelvic diaphragm. Note also that the region of the main pelvic cavity lies above the pelvic diaphragm and the region of the perineum lies below the diaphragm.
Figure 8-2 Diamond-shaped perineum divided by a broken line into the urogenital triangle and the anal triangle.

Structure The mucous membrane of the upper half of the anal canal is derived from hindgut entoderm (Fig. 8-6). It has the following important anatomic features:

  • It is lined by columnar epithelium.
  • It is thrown into vertical folds called anal columns, which are joined together at their lower ends by small semilunar folds called anal valves (remains of proctodeal membrane) (Figs. 8-5 and 8-7).
  • The nerve supply is the same as that for the rectal mucosa and is derived from the autonomic hypogastric plexuses. It is sensitive only to stretch (Fig. 8-6).
  • The arterial supply is that of the hindgut—namely, the superior rectal artery, a branch of the inferior mesenteric artery (Fig. 8-6). The venous drainage is mainly by the superior rectal vein, a tributary of the inferior mesenteric vein, and the portal vein (Fig. 8-5).
  • The lymphatic drainage is mainly upward along the superior rectal artery to the pararectal nodes and then eventually to the inferior mesenteric nodes (Fig. 8-6).

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Figure 8-3 Anal triangle and urogenital triangle in the male as seen from below.
Figure 8-4 Sagittal sections of the male (A) pelvis. Sagittal sections of the female (B) pelvis.

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Figure 8-5 Coronal section of the pelvis and the perineum showing venous drainage of the anal canal.

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Figure 8-6 Upper and lower halves of the anal canal showing their embryologic origin and lining epithelium (A), their arterial supply (B), their venous drainage (C), and their lymph drainage (D). E. Arrangement of the muscle fibers of the puborectalis muscle and different parts of the external anal sphincter.

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Figure 8-7 Coronal section of the anal canal showing the detailed anatomy of the mucous membrane and the arrangement of the internal and external anal sphincters. Note that the terms pectinate line (the line at the level of the anal valves) and pecten (the transitional zone between the skin and the mucous membrane) are sometimes used by clinicians.

The mucous membrane of the lower half of the anal canal is derived from ectoderm of the proctodeum. It has the following important features:

  • It is lined by stratified squamous epithelium, which gradually merges at the anus with the perianal epidermis (Fig. 8-6).
  • There are no anal columns (Fig. 8-7).
  • The nerve supply is from the somatic inferior rectal nerve; it is thus sensitive to pain, temperature, touch, and pressure (Figs. 8-3 and 8-6).
  • The arterial supply is the inferior rectal artery, a branch of the internal pudendal artery (Fig. 8-3). The venous drainage is by the inferior rectal vein, a tributary of the internal pudendal vein, which drains into the internal iliac vein (Figs. 8-5 and 8-6).
  • The lymph drainage is downward to the medial group of superficial inguinal nodes (Fig. 8-6).

The pectinate line indicates the level where the upper half of the anal canal joins the lower half (Fig. 8-7). Muscle Coat As in the upper parts of the intestinal tract, it is divided into an outer longitudinal and an inner circular layer of smooth muscle (Fig. 8-5). Anal Sphincters The anal canal has an involuntary internal sphincter and a voluntary external sphincter. The internal sphincter is formed from a thickening of the smooth muscle of the circular coat at the upper end of the anal canal. The internal sphincter is enclosed by a sheath of striped muscle that forms the voluntary external sphincter (Figs. 8-5, 8-6, and 8-7). The external sphincter can be divided into three parts:

  • A subcutaneous part, which encircles the lower end of the anal canal and has no bony attachments
  • A superficial part, which is attached to the coccyx behind and the perineal body in front
  • A deep part, which encircles the upper end of the anal canal and has no bony attachments

The puborectalis fibers of the two levatores ani muscles blend with the deep part of the external sphincter (Figs. 8-5, 8-6, and 8-7). The puborectalis fibers of the two sides form a sling, which is attached in front to the pubic bones and passes around the junction of the rectum and the anal canal, pulling the two forward at an acute angle (Fig. 8-6). The longitudinal smooth muscle of the anal canal is continuous above with that of the rectum. It forms a continuous coat around the anal canal and descends in the interval P.394
between the internal and external anal sphincters. Some of the longitudinal fibers are attached to the mucous membrane of the anal canal, whereas others pass laterally into the ischiorectal fossa or are attached to the perianal skin (Fig. 8-5). At the junction of the rectum and anal canal (Fig. 8-6), the internal sphincter, the deep part of the external sphincter, and the puborectalis muscles form a distinct ring, called the anorectal ring, which can be felt on rectal examination. Blood Supply Arteries The superior artery supplies the upper half and the inferior artery supplies the lower half (Fig. 8-6). Veins The upper half is drained by the superior rectal vein into the inferior mesenteric vein and the lower half is drained by the inferior rectal vein into the internal pudendal vein. Lymph Drainage The upper half of the anal canal drains into the pararectal nodes and then the inferior mesenteric nodes. The lower half drains into the medial group of superficial inguinal nodes (Fig. 8-6). Nerve Supply The mucous membrane of the upper half is sensitive to stretch and is innervated by sensory fibers that ascend through the hypogastric plexuses. The lower half is sensitive to pain, temperature, touch, and pressure and is innervated by the inferior rectal nerves. The involuntary internal sphincter is supplied by sympathetic fibers from the inferior hypogastric plexuses. The voluntary external sphincter is supplied by the inferior rectal nerve, a branch of the pudendal nerve (Fig. 8-3), and the perineal branch of the fourth sacral nerve. Defecation The time, place, and frequency of defecation are a matter of habit. Some adults defecate once a day, some defecate several times a day, and some perfectly normal people defecate once in several days. The desire to defecate is initiated by stimulation of the stretch receptors in the wall of the rectum by the presence of feces in the lumen. The act of defecation involves a coordinated reflex that results in the emptying of the descending colon, sigmoid colon, rectum, and anal canal. It is assisted by a rise in intra-abdominal pressure brought about by contraction of the muscles of the anterior abdominal wall. The tonic contraction of the internal and external anal sphincters, including the puborectalis muscles, is now voluntarily inhibited, and the feces are evacuated through the anal canal. Depending on the laxity of the submucous coat, the mucous membrane of the lower part of the anal canal is extruded through the anus ahead of the fecal mass. At the end of the act, the mucosa is returned to the anal canal by the tone of the longitudinal fibers of the anal walls and the contraction and upward pull of the puborectalis muscle. The empty lumen of the anal canal is now closed by the tonic contraction of the anal sphincters. Ischiorectal Fossa The ischiorectal fossa (ischioanal fossa) is a wedge-shaped space located on each side of the anal canal (Fig. 8-5). The base of the wedge is superficial and formed by the skin. The edge of the wedge is formed by the junction of the medial and lateral walls. The medial wall is formed by the sloping levator ani muscle and the anal canal. The lateral wall is formed by the lower part of the obturator internus muscle, covered with pelvic fascia. Contents of Fossa The ischiorectal fossa is filled with dense fat, which supports the anal canal and allows it to distend during defecation. The pudendal nerve and internal pudendal vessels are embedded in a fascial canal, the pudendal canal, on the lateral wall of the ischiorectal fossa, on the medial side of the ischial tuberosity (Figs. 8-5 and 8-8). The inferior rectal vessels and nerve cross the fossa to reach the anal canal. Pudendal Nerve The pudendal nerve is a branch of the sacral plexus and leaves the main pelvic cavity through the greater sciatic foramen (Fig. 8-8). After a brief course in the gluteal region of the lower limb, it enters the perineum through the lesser sciatic foramen. The nerve then passes forward in the pudendal canal and, by means of its branches, supplies the external anal sphincter and the muscles and skin of the perineum. Branches

  • Inferior rectal nerve: This runs medially across the ischiorectal fossa and supplies the external anal sphincter, the mucous membrane of the lower half of the anal canal, and the perianal skin (Fig. 8-3).
  • Dorsal nerve of the penis (or clitoris): This is distributed to the penis (or clitoris) (Fig. 8-8).
  • Perineal nerve: This supplies the muscles in the urogenital triangle (Fig. 8-8) and the skin on the posterior surface of the scrotum (or labia majora).

Internal Pudendal Artery The internal pudendal artery is a branch of the internal iliac artery and passes from the pelvis through the greater sciatic foramen and enters the perineum through the lesser sciatic foramen. Branches

  • Inferior rectal artery: This supplies the lower half of the anal canal (Fig. 8-3).
  • Branches to the penis in the male and to the labia and clitoris in the female

Internal Pudendal Vein The internal pudendal vein receives tributaries that correspond to the branches of the internal pudendal artery. P.395

Figure 8-8 Course and branches of the pudendal nerve in the male.

Clinical Notes Portal–Systemic Anastomosis The rectal veins form an important portal–systemic anastomosis because the superior rectal vein drains ultimately into the portal vein and the inferior rectal vein drains into the systemic system. Internal Hemorrhoids (Piles) Internal hemorrhoids are varicosities of the tributaries of the superior rectal (hemorrhoidal) vein and are covered by mucous membrane (Fig. 8-9). The tributaries of the vein, which lie in the anal columns at the 3-, 7-, and 11-o’clock positions when the patient is viewed in the lithotomy position,* are particularly liable to become varicosed. Anatomically, a hemorrhoid is therefore a fold of mucous membrane and submucosa containing a varicosed tributary of the superior rectal vein and a terminal branch of the superior rectal artery. Internal hemorrhoids are initially contained within the anal canal (first degree). As they enlarge, they extrude from the canal on defecation but return at the end of the act (second degree). With further elongation, they prolapse on defecation and remain outside the anus (third degree). Because internal hemorrhoids occur in the upper half of the anal canal, where the mucous membrane is innervated by autonomic afferent nerves, they are painless and are sensitive only to stretch. This may explain why large internal hemorrhoids give rise to an aching sensation rather than acute pain. The causes of internal hemorrhoids are many. They frequently occur in members of the same family, which suggests a congenital weakness of the vein walls. Varicose veins of the legs and hemorrhoids often go together. The superior rectal vein is the most dependent part of the portal circulation and is valveless. The weight of the column of venous blood is thus greatest in the veins in the upper half of the anal canal. Here, the loose connective tissue of the submucosa gives little support to the walls of the veins. Moreover, the venous return is interrupted by the contraction of the muscular coat of the rectal wall during defecation. Chronic constipation, associated with prolonged straining at stool, is a common predisposing factor. Pregnancy hemorrhoids are common owing to pressure on the superior rectal veins by the gravid uterus. Portal hypertension as a result of cirrhosis of the liver can also cause hemorrhoids. The possibility that cancerous tumors of the rectum are blocking the superior rectal vein must never be overlooked. External Hemorrhoids External hemorrhoids are varicosities of the tributaries of the inferior rectal (hemorrhoidal) vein as they run laterally from the anal margin. They are covered by skin (Fig. 8-9) and are commonly associated with well-established internal hemorrhoids. External hemorrhoids are covered by the mucous membrane of the lower half of the anal canal or the skin, and they are innervated by the inferior rectal nerves. They are sensitive to pain, temperature, touch, and pressure, which explains why external hemorrhoids tend to be painful. Thrombosis of an external hemorrhoid is common. Its cause is unknown, although coughing or straining may produce distention of the hemorrhoid followed by stasis. The presence of a small, acutely tender swelling at the anal margin is immediately recognized by the patient. Perianal Hematoma A perianal hematoma is a small collection of blood beneath the perianal skin (Fig. 8-9). It is caused by a rupture of a small subcutaneous vein, possibly an external hemorrhoid, and is extremely painful. Anal Fissure The lower ends of the anal columns are connected by small folds called anal valves (Fig. 8-10). In people suffering from chronic constipation, the anal valves may be torn down to the anus as the result of the edge of the fecal mass catching on the fold of mucous membrane. The elongated ulcer so formed, known as an anal fissure (Fig. 8-10), is extremely painful. The fissure occurs most commonly in the midline posteriorly or, less commonly, anteriorly, and this may be caused by the lack of support provided by the superficial part of the external sphincter in these areas. (The superficial part of the external sphincter does not encircle the anal canal, but sweeps past its lateral sides.) The site of the anal fissure in the sensitive lower half of the anal canal, which is innervated by the inferior rectal nerve, results in reflex spasm of the external anal sphincter, aggravating the condition. Because of the intense pain, anal fissures may have to be examined under local anesthesia. Perianal Abscesses Perianal abscesses are produced by fecal trauma to the anal mucosa (Fig. 8-10). Infection may gain entrance to the submucosa through a small mucosal lesion, or the abscess may complicate an anal fissure or the infection of an anal mucosal gland. The abscess may be localized to the submucosa (submucous abscess), may occur beneath the perianal skin (subcutaneous abscess), or may occupy the ischiorectal fossa (ischiorectal abscess). Large ischiorectal abscesses sometimes extend posteriorly around the side of the anal canal to invade the ischiorectal fossa of the opposite side (horseshoe abscess). An abscess may be found in the space between the ampulla of the rectum and the upper surface of the levator ani (pelvirectal abscess). Anatomically, these abscesses are closely related to the different parts of the external sphincter and levator ani muscles, as seen in Figure 8-10. Anal fistulae develop as the result of spread or inadequate treatment of anal abscesses. The fistula opens at one end at the lumen of the anal canal or lower rectum and at the other end on the skin surface close to the anus (Fig. 8-10). If the abscess opens onto only one surface, it is known as a sinus, not a fistula. The high-level fistulae are rare and run from the rectum to the perianal skin. They are located above the anorectal ring; as a result, fecal material constantly soils the clothes. The low-level fistulae occur below the level of the anorectal ring, as shown in Figure 8-10. The most important part of the sphincteric mechanism of the anal canal is the anorectal ring. It consists of the deep part of the external sphincter, the internal sphincter, and the puborectalis part of the levator ani. Surgical operations on the anal canal that result in damage to the anorectal ring will produce fecal incontinence. Removal of Anorectal Foreign Bodies Normally, the anal canal is kept closed by the tone of the internal and external anal sphincters and the tone of the puborectalis part of the levator ani muscles. The rectal contents are supported by the levator ani muscles, possibly assisted by the transverse rectal mucosal folds. For these reasons, the removal of a large foreign body, such as a vase or electric light bulb, from the rectum may be a formidable problem. The following procedure is usually successful:

  • The foreign body must first be fixed so that the sphincteric tone, together with external attempts to grab the object, do not displace the object farther up the rectum.
  • Large, irregular, or fragile foreign bodies may not be removed so easily, and it may be necessary to paralyze the anal sphincter by giving the patient a general anesthetic or by performing an anal sphincter nerve block.

Anal Sphincter Nerve Block and Anesthetizing the Perianal Skin By blocking the branches of the inferior rectal nerve and the perineal branch of the fourth sacral nerve, the anal sphincters will be relaxed and the perianal skin anesthetized. The procedure is as follows:

  • An intradermal wheal is produced by injecting a small amount of anesthetic solution behind the anus in the midline.
  • A gloved index finger is inserted into the anal canal to serve as a guide.
  • A long needle attached to a syringe filled with anesthetic solution is inserted through the cutaneous wheal into the sphincter muscles along the posterior and lateral surfaces of the anal canal. The procedure is repeated on the opposite side. The purpose of the finger in the anal canal is to guide the needle and to prevent penetration of the anal mucous membrane.

Incontinence Associated with Rectal Prolapse Fecal incontinence can accompany severe rectal prolapse of long duration. It is thought that the prolonged and excessive stretching of the anal sphincters is the cause of the condition. The condition can be treated by restoring the anorectal angle by tightening the puborectalis part of the levator ani muscles and the external anal sphincters behind the anorectal junction. Incontinence After Trauma Trauma, such as childbirth, or damage to the sphincters during surgery or perianal abscesses or fistulae can be responsible for incontinence after trauma. Incontinence After Spinal Cord Injury After severe spinal cord injuries, the patient is not aware of rectal distention. Moreover, the parasympathetic influence on the peristaltic activity of the descending colon, sigmoid colon, and rectum is lost. In addition, control over the abdominal musculature and sphincters of the anal canal may be severely impaired. The rectum, now an isolated structure, responds by contracting when the pressure within its lumen rises. This local reflex response is much more efficient if the sacral segments of the spinal cord are spared. At best, however, the force of the contractions of the rectal wall is small, and constipation and impaction of feces are the usual outcome. Rectal Examination The following structures can be palpated by the gloved index finger inserted into the anal canal and rectum in the normal patient. Anteriorly In the male:

  • Opposite the terminal phalanx are the contents of the rectovesical pouch, the posterior surface of the bladder, the seminal vesicles, and the vasa deferentia (Fig. 8-11).
  • Opposite the middle phalanx are the rectoprostatic fascia and the prostate.
  • Opposite the proximal phalanx are the perineal body, the urogenital diaphragm, and the bulb of the penis.

In the female:

  • Opposite the terminal phalanx are the rectouterine pouch, the vagina, and the cervix.
  • Opposite the middle phalanx are the urogenital diaphragm and the vagina.
  • Opposite the proximal phalanx are the perineal body and the lower part of the vagina.

Posteriorly The sacrum, coccyx, and anococcygeal body can be felt. Laterally The ischiorectal fossae and ischial spines can be palpated. Cancer and the Lymph Drainage of the Anal Canal The upper half of the mucous membrane of the anal canal is drained upward to lymph nodes along the course of the superior rectal artery. The lower half of the mucous membrane is drained downward to the medial group of superficial inguinal nodes. Many patients have thought they had an inguinal hernia, and the physician has found a cancer of the lower half of the anal canal, with secondary deposits in the inguinal lymph nodes. The Ischiorectal Fossa and Infection The ischiorectal fossae (ischioanal fossae) are filled with fat that is poorly vascularized. The close proximity to the anal canal makes them particularly vulnerable to infection. Infection commonly tracks laterally from the anal mucosa through the external anal sphincter. Infection of the perianal hair follicles or sweat glands may also be the cause of infection in the fossae. Rarely, a perirectal abscess bursts downward through the levator ani muscle. An ischiorectal abscess may involve the opposite fossa by the spread of infection across the midline behind the anal canal. Footnote * The patient is in the supine position with both hip joints flexed and abducted; the feet are held in position by stirrups. The position is commonly used for pelvic examinations of the female. P.396
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Embryologic Notes Development of the Anal Canal The distal end of the hindgut terminates as a blind sac of entoderm called the cloaca (see Fig. 7-8). The cloaca lies in contact with a shallow ectodermal depression called the proctodeum. The apposed layers of ectoderm and entoderm form the cloacal membrane, which separates the cavity of the hindgut from the surface (see Fig. 7-8). The cloaca becomes divided into anterior and posterior parts by the urorectal septum; the posterior part of the cloaca is called the anorectal canal. The anorectal canal forms the rectum and the upper half of the anal canal. The lining of the superior half of the anal canal is formed from entoderm, and that of the inferior half of the anal canal is formed from the ectoderm of the proctodeum (see Fig. 7-8). The sphincters of the anal canal are formed from the surrounding mesenchyme. The posterior part of the cloacal membrane breaks down so that the gut opens onto the surface of the embryo. Imperforate Anus About 1 child in 4000 is born with imperforate anus caused by an imperfect fusion of the entodermal cloaca with the proctodeum. P.398

Figure 8-9 A. Normal tributary of the superior rectal vein within the anal column. B. Varicosed tributary of the superior rectal vein forming the internal hemorrhoid. Dotted lines indicate degrees of severity of condition. C. Positions of three internal hemorrhoids as seen through a proctoscope with the patient in the lithotomy position.

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Figure 8-10 A. Tearing downward of the anal valve to form an anal fissure. B. Common locations of perianal abscesses. C. Common positions of perianal fistulae.

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Figure 8-11 A. Rectal examination in a pregnant woman showing how it is possible to palpate the cervix through the anterior rectal wall. B. Rectal examination in the male showing how it is possible to palpate the prostate and the seminal vesicles through the anterior rectal wall. C. Position of the episiotomy incision in a woman during the second stage of labor. The baby’s head is presenting at the vaginal orifice.

Urogenital Triangle The urogenital triangle is bounded in front by the pubic arch and laterally by the ischial tuberosities (Fig. 8-3). Superficial Fascia The superficial fascia of the urogenital triangle can be divided into a fatty layer and a membranous layer. The fatty layer (fascia of Camper) is continuous with the fat of the ischiorectal fossa (Fig. 8-12) and the superficial fascia of the thighs. In the scrotum, the fat is replaced by smooth muscle, the dartos muscle. The dartos muscle contracts in response to cold and reduces the surface area of the scrotal skin (see testicular temperature and fertility, page 169). The membranous layer (Colles’ fascia) is attached posteriorly to the posterior border of the urogenital diaphragm (Fig. 8-12) and laterally to the margins of the pubic arch; anteriorly it is continuous with the membranous layer of superficial fascia of the anterior abdominal wall (Scarpa’s fascia). The fascia is continued over the penis (or clitoris) as a tubular sheath (Fig. 8-13). In the scrotum (or labia majora) it forms a distinct layer (Fig. 8-12). P.401

Figure 8-12 Arrangement of the superficial fascia in the urogenital triangle. Note the superficial and deep perineal pouches.

Superficial Perineal Pouch The superficial perineal pouch is bounded below by the membranous layer of superficial fascia and above by the urogenital diaphragm (Fig. 8-12). It is closed behind by the fusion of its upper and lower walls. Laterally, it is closed by the attachment of the membranous layer of superficial fascia and the urogenital diaphragm to the margins of the pubic arch (Figs. 8-14 and 8-15). Anteriorly, the space communicates freely with the potential space lying between the superficial fascia of the anterior abdominal wall and the anterior abdominal muscles. The contents of the superficial perineal pouch in both sexes are described on pages 405 and 408. Urogenital Diaphragm The urogenital diaphragm is a triangular musculofascial diaphragm situated in the anterior part of the perineum, filling in the gap of the pubic arch (Figs. 8-12, 8-14, and 8-15). It is formed by the sphincter urethrae and the deep transverse perineal muscles, which are enclosed between a superior and an inferior layer of fascia of the urogenital diaphragm. The inferior layer of fascia is often referred to as the perineal membrane. Anteriorly, the two layers of fascia fuse, leaving a small gap beneath the symphysis pubis. Posteriorly, the two layers of fascia fuse with each other and with the membranous layer of the superficial fascia and the perineal body (Fig. 8-12). P.402
Laterally, the layers of fascia are attached to the pubic arch. The closed space that is contained between the superficial and deep layers of fascia is known as the deep perineal pouch (Figs. 8-12, 8-14, and 8-15).

Figure 8-13 The penis. A and B. The three bodies of erectile tissue, the two corpora cavernosa, and the corpus spongiosum with the glans. C. The penile urethra slit open to show the folds of mucous membrane and glandular orifices in the roof of the urethra.

The contents of the deep perineal pouch in both sexes are described in subsequent sections. Contents of the Male Urogenital Triangle In the male, the triangle contains the penis and scrotum. Penis Location and Description The penis has a fixed root and a body that hangs free (Figs. 8-4 and 8-16). P.403
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Root of the Penis The root of the penis is made up of three masses of erectile tissue called the bulb of the penis and the right and left crura of the penis (Figs. 8-13, 8-16, and 8-17). The bulb is situated in the midline and is attached to the undersurface of the urogenital diaphragm. It is traversed by the urethra and is covered on its outer surface by the bulbospongiosus muscles. Each crus is attached to the side of the pubic arch and is covered on its outer surface by the ischiocavernosus muscle. The bulb is continued forward into the body of the penis and forms the corpus spongiosum (Fig. 8-17). The two crura converge anteriorly and come to lie side by side in the dorsal part of the body of the penis, forming the corpora cavernosa (Figs. 8-13 and 8-16).

Figure 8-14 Coronal section of the male pelvis showing the prostate, the urogenital diaphragm, and the contents of the superficial perineal pouch.
Figure 8-15 Coronal section of the female pelvis showing the vagina, the urogenital diaphragm, and the contents of the superficial perineal pouch.
Figure 8-16 Root and body of the penis.
Figure 8-17 Root of penis and perineal muscles.

Body of the Penis The body of the penis is essentially composed of three cylinders of erectile tissue enclosed in a tubular sheath of fascia (Buck’s fascia). The erectile tissue is made up of two dorsally placed corpora cavernosa and a single corpus spongiosum applied to their ventral surface (Figs. 8-13 and 8-16). At its distal extremity, the corpus spongiosum expands to form the glans penis, which covers the distal ends of the corpora cavernosa. On the tip of the glans penis is the slitlike orifice of the urethra, called the external urethral meatus. The prepuce or foreskin is a hoodlike fold of skin that covers the glans. It is connected to the glans just below the urethral orifice by a fold called the frenulum. The body of the penis is supported by two condensations of deep fascia that extend downward from the linea alba and symphysis pubis to be attached to the fascia of the penis. Blood Supply Arteries The corpora cavernosa are supplied by the deep arteries of the penis (Fig. 8-13); the corpus spongiosum is supplied by the artery of the bulb. In addition, there is the dorsal artery of the penis. All the above arteries are branches of the internal pudendal artery. Veins The veins drain into the internal pudendal veins. Lymph Drainage The skin of the penis is drained into the medial group of superficial inguinal nodes. The deep structures of the penis are drained into the internal iliac nodes. Nerve Supply The nerve supply is from the pudendal nerve and the pelvic plexuses. Scrotum Location and Description The scrotum is an outpouching of the lower part of the anterior abdominal wall and contains the testes, the epididymides, and the lower ends of the spermatic cords (see Fig. 4-21). The wall of the scrotum has the following layers:

  • Skin
  • Superficial fascia; the dartos muscle, which is smooth muscle, replaces the fatty layer of the anterior abdominal wall, and Scarpa’s fascia (membranous layer) is now called Colles’ fascia.
  • External spermatic fascia derived from the external oblique
  • Cremasteric fascia derived from the internal oblique
  • Internal spermatic fascia derived from the fascia transversalis
  • Tunica vaginalis, which is a closed sac that covers the anterior, medial, and lateral surfaces of each testis

Because the structure of the scrotum, the descent of the testes, and the formation of the inguinal canal are interrelated, they are fully described in Chapter 4. Blood Supply Subcutaneous plexuses and arteriovenous anastomoses promote heat loss and thus assist in the environmental control of the temperature of the testes. Arteries The external pudendal branches of the femoral and scrotal branches of the internal pudendal arteries supply the scrotum. Veins The veins accompany the corresponding arteries. Lymph Drainage The wall of the scrotum is drained into the medial group of superficial inguinal lymph nodes. The lymph drainage of the testis and epididymis ascends in the spermatic cord and ends in the lumbar (para-aortic) lymph nodes at the level of the first lumbar vertebra. This is to be expected, because the testis during development has migrated from high up on the posterior abdominal wall, down through the inguinal canal, and into the scrotum, dragging its blood supply and lymph vessels after it. Nerve Supply The anterior surface of the scrotum is supplied by the ilioinguinal nerves and the genital branch of the genitofemoral nerves, and the posterior surface is supplied by branches of the perineal nerves and the posterior cutaneous nerves of the thigh. Contents of the Superficial Perineal Pouch in the Male The superficial perineal pouch contains structures forming the root of the penis, together with the muscles that cover them—namely, the bulbospongiosus muscles and the ischiocavernosus muscles (Fig. 8-17). The bulbospongiosus muscles, situated one on each side of the midline (Fig. 8-17), cover the bulb of the penis and the posterior portion of the corpus spongiosum. Their function is to compress the penile part of the urethra and empty it of residual urine or semen. The anterior fibers also compress the deep dorsal vein of the penis, thus impeding the venous drainage of the erectile tissue and thereby assisting in the process of erection of the penis. Ischiocavernosus Muscles The ischiocavernosus muscles cover the crus penis on each side (Fig. 8-17). The action of each muscle is to compress the crus penis and assist in the process of erection of the penis. Superficial Transverse Perineal Muscles The superficial transverse perineal muscles lie in the posterior part of the superficial perineal pouch (Fig. 8-17). Each muscle arises from the ischial ramus and is inserted into the perineal body. The function of these muscles is to fix the perineal body in the center of the perineum. Nerve Supply All the muscles of the superficial perineal pouch are supplied by the perineal branch of the pudendal nerve. P.406
Perineal Body This small mass of fibrous tissue is attached to the center of the posterior margin of the urogenital diaphragm (Figs. 8-12 and 8-17). It serves as a point of attachment for the following muscles: external anal sphincter, bulbospongiosus muscle, and superficial transverse perineal muscles. Perineal Branch of the Pudendal Nerve The perineal branch of the pudendal nerve on each side terminates in the superficial perineal pouch by supplying the muscles and skin (Fig. 8-8). Contents of the Deep Perineal Pouch in the Male The deep perineal pouch contains the membranous part of the urethra, the sphincter urethrae, the bulbourethral glands, the deep transverse perineal muscles, the internal pudendal vessels and their branches, and the dorsal nerves of the penis. Membranous Part of the Urethra The membranous part of the urethra is about 0.5 in. (1.3 cm) long and lies within the urogenital diaphragm, surrounded by the sphincter urethrae muscle; it is continuous above with the prostatic urethra and below with the penile urethra. It is the shortest and least dilatable part of the urethra (Fig. 8-14). Sphincter Urethrae Muscle The sphincter urethrae muscle surrounds the urethra in the deep perineal pouch. It arises from the pubic arch on the two sides and passes medially to encircle the urethra (Fig. 8-14). Nerve Supply The perineal branch of the pudendal nerve supplies the sphincter. Action The muscle compresses the membranous part of the urethra and relaxes during micturition. It is the means by which micturition can be voluntarily stopped. Bulbourethral Glands The bulbourethral glands are two small glands that lie beneath the sphincter urethrae muscle (Fig. 8-14). Their ducts pierce the perineal membrane (inferior fascial layer of the urogenital diaphragm) and enter the penile portion of the urethra. The secretion is poured into the urethra as a result of erotic stimulation. Deep Transverse Perineal Muscles The deep transverse perineal muscles lie posterior to the sphincter urethrae muscle. Each muscle arises from the ischial ramus and passes medially to be inserted into the perineal body. These muscles are clinically unimportant. Internal Pudendal Artery The internal pudenal artery (Fig. 8-14) on each side enters the deep perineal pouch and passes forward, giving rise to the artery to the bulb of the penis; the arteries to the crura of the penis (deep artery of penis); and the dorsal artery of the penis, which supplies the skin and fascia of the penis. Dorsal Nerve of the Penis The dorsal nerve of the penis on each side passes forward through the deep perineal pouch and supplies the skin of the penis (Fig. 8-14). Erection of the Penis Erection in the male is gradually built up as a consequence of various sexual stimuli. Pleasurable sight, sound, smell, and other psychic stimuli, fortified later by direct touch sensory stimuli from the general body skin and genital skin, result in a bombardment of the central nervous system by afferent stimuli. Efferent nervous impulses pass down the spinal cord to the parasympathetic outflow in the second, third, and fourth sacral segments. The parasympathetic preganglionic fibers enter the inferior hypogastric plexuses and synapse on the postganglionic neurons. The postganglionic fibers join the internal pudendal arteries and are distributed along their branches, which enter the erectile tissue at the root of the penis. Vasodilatation of the arteries now occurs, producing a great increase in blood flow through the blood spaces of the erectile tissue. The corpora cavernosa and the corpus spongiosum become engorged with blood and expand, compressing their draining veins against the surrounding fascia. By this means, the outflow of blood from the erectile tissue is retarded so that the internal pressure is further accentuated and maintained. The penis thus increases in length and diameter and assumes the erect position. Once the climax of sexual excitement is reached and ejaculation takes place, or the excitement passes off or is inhibited, the arteries supplying the erectile tissue undergo vasoconstriction. The penis then returns to its flaccid state. Ejaculation During the increasing sexual excitement that occurs during sex play, the external urinary meatus of the glans penis becomes moist as a result of the secretions of the bulbourethral glands. Friction on the glans penis, reinforced by other afferent nervous impulses, results in a discharge along the sympathetic nerve fibers to the smooth muscle of the duct of the epididymis and the vas deferens on each side, the seminal vesicles, and the prostate. The smooth muscle contracts, and the spermatozoa, together with the secretions of the seminal vesicles and prostate, are discharged into the prostatic urethra. The fluid now joins the secretions of the bulbourethral glands and penile urethral glands and is then ejected from the penile urethra as a result of the rhythmic contractions of the bulbospongiosus muscles, which compress the urethra. Meanwhile, the sphincter of the bladder contracts and prevents a reflux of the spermatozoa into the bladder. The spermatozoa and the secretions of the several accessory glands constitute the seminal fluid, or semen. At the climax of male sexual excitement, a mass discharge of nervous impulses takes place in the central nervous system. Impulses pass down the spinal cord to the sympathetic outflow (T1 to L2). The nervous impulses that pass to the genital organs are thought to leave the cord at the first and second lumbar segments in the preganglionic sympathetic fibers. Many of these fibers synapse with postganglionic neurons in the first and second lumbar ganglia. Other fibers may synapse in ganglia in the lower lumbar or pelvic parts of the sympathetic trunks. The postganglionic P.407
fibers are then distributed to the vas deferens, the seminal vesicles, and the prostate via the inferior hypogastric plexuses. Male Urethra The male urethra is about 8 in. (20 cm) long and extends from the neck of the bladder to the external meatus on the glans penis (Fig. 8-4). It is divided into three parts: prostatic, membranous, and penile. The prostatic urethra is described on page 356. It is about 1.25 in. (3 cm) long and passes through the prostate from the base to the apex (Fig. 8-14). It is the widest and most dilatable portion of the urethra. The membranous urethra is about 0.5 in. (1.25 cm) long and lies within the urogenital diaphragm, surrounded by the sphincter urethrae muscle. It is the least dilatable portion of the urethra (Fig. 8-14). The penile urethra is about 6 in. (15.75 cm) long and is enclosed in the bulb and the corpus spongiosum of the penis (Figs. 8-4, 8-14, 8-16, and 8-17). The external meatus is the narrowest part of the entire urethra. The part of the urethra that lies within the glans penis is dilated to form the fossa terminalis (navicular fossa) (Fig. 8-4). The bulbourethral glands open into the penile urethra below the urogenital diaphragm. Clinical Notes Circumcision Circumcision is the operation of removing the greater part of the prepuce, or foreskin. In many newborn males, the prepuce cannot be retracted over the glans. This can result in infection of the secretions beneath the prepuce, leading to inflammation, swelling, and fibrosis of the prepuce. Repeated inflammation leads to constriction of the orifice of the prepuce (phimosis) with obstruction to urination. It is now generally believed that chronic inflammation of the prepuce predisposes to carcinoma of the glans penis. For these reasons prophylactic circumcision is commonly practiced. For Jews, it is a religious rite. Catheterization of the Male The following anatomic facts should be remembered before passing a catheter or other instrument along the male urethra:

  • The external orifice at the glans penis is the narrowest part of the entire urethra.
  • Within the glans, the urethra dilates to form the fossa terminalis (navicular fossa).
  • Near the posterior end of the fossa, a fold of mucous membrane projects into the lumen from the roof (Fig. 8-13).
  • The membranous part of the urethra is narrow and fixed.
  • The prostatic part of the urethra is the widest and most dilatable part of the urethra.
  • By holding the penis upward, the S-shaped curve to the urethra is converted into a J-shaped curve.

If the point of the catheter passes through the external orifice and is then directed toward the urethral floor until it has passed the mucosal fold, it should easily pass along a normal urethra into the bladder. Anatomy of the Procedure of Catheterization The procedure is as follows:

  • The patient lies in a supine position.
  • With gentle traction, the penis is held erect at right angles to the anterior abdominal wall. The lubricated catheter is passed through the narrow external urethral meatus. The catheter should pass easily along the penile urethra. On reaching the membranous part of the urethra, a slight resistance is felt because of the tone of the urethral sphincter and the surrounding rigid perineal membrane.
  • The penis is then lowered toward the thighs, and the catheter is gently pushed through the sphincter.
  • Passage of the catheter through the prostatic urethra and bladder neck should not present any difficulty.

Urethral Infection The most dependent part of the male urethra is that which lies within the bulb. Here, it is subject to chronic inflammation and stricture formation. The many glands that open into the urethra—including those of the prostate, the bulbourethral glands, and many small penile urethral glands—are commonly the site of chronic gonococcal infection. Injuries to the penis may occur as the result of blunt trauma, penetrating trauma, or strangulation. Amputation of the entire penis should be repaired by anastomosis using microsurgical techniques to restore continuity of the main blood vessels. Rupture of the Urethra Rupture of the urethra may complicate a severe blow on the perineum. The common site of rupture is within the bulb of the penis, just below the perineal membrane. The urine extravasates into the superficial perineal pouch and then passes forward over the scrotum beneath the membranous layer of the superficial fascia, as described in Chapter 4. If the membranous part of the urethra is ruptured, urine escapes into the deep perineal pouch and can extravasate upward around the prostate and bladder or downward into the superficial perineal pouch. Erection and Ejaculation After Spinal Cord Injuries Erection of the penis is controlled by the parasympathetic nerves that originate from the second, third, and fourth sacral segments of the spinal cord. Bilateral damage to the reticulospinal nerve tracts in the spinal cord will result in loss of erection. Later, when the effects of spinal shock have disappeared, spontaneous or reflex erection may occur if the sacral segments of the spinal cord are intact. Ejaculation is controlled by sympathetic nerves that originate in the first and second lumbar segments of the spinal cord. As in the case of erection, severe bilateral damage to the spinal cord results in loss of ejaculation. Later, reflex ejaculation may be possible in patients with spinal cord transections in the thoracic or cervical regions. Scrotum see page 167. P.408
Contents of the Female Urogenital Triangle In the female, the triangle contains the external genitalia and the orifices of the urethra and the vagina. Clitoris Location and Description The clitoris, which corresponds to the penis in the male, is situated at the apex of the vestibule anteriorly. It has a structure similar to the penis. The glans of the clitoris is partly hidden by the prepuce. Root of the Clitoris The root of the clitoris is made up of three masses of erectile tissue called the bulb of the vestibule and the right and left crura of the clitoris (Figs. 8-15 and 8-18). The bulb of the vestibule corresponds to the bulb of the penis, but because of the presence of the vagina, it is divided into two halves (Fig. 8-18). It is attached to the undersurface of the urogenital diaphragm and is covered by the bulbospongiosus muscles. The crura of the clitoris correspond to the crura of the penis and become the corpora cavernosa anteriorly. Each remains separate and is covered by an ischiocavernosus muscle (Fig. 8-18).

Figure 8-18 Root and body of the clitoris and the perineal muscles.

Body of the Clitoris The body of the clitoris consists of the two corpora cavernosa covered by their ischiocavernosus muscles. The corpus spongiosum of the male is represented by a small amount of erectile tissue leading from the vestibular bulbs to the glans. Glans of the Clitoris The glans of the clitoris is a small mass of erectile tissue that caps the body of the clitoris. It is provided with numerous sensory endings. The glans is partly hidden by the prepuce. Blood Supply, Lymph Drainage, and Nerve Supply The blood supply, lymph drainage, and nerve supply are similar to those of the penis. Contents of the Superficial Perineal Pouch in the Female The superficial perineal pouch contains structures forming the root of the clitoris and the muscles that cover them, namely, the bulbospongiosus muscles and the ischiocavernosus muscles (Figs. 8-15 and 8-18). Bulbospongiosus Muscle The bulbospongiosus muscle surrounds the orifice of the vagina and covers the vestibular bulbs. Its fibers extend forward to gain attachment to the corpora cavernosa of the clitoris. The bulbospongiosus muscle reduces the size of the vaginal orifice and compresses the deep dorsal vein of the P.409
clitoris, thereby assisting in the mechanism of erection in the clitoris. Ischiocavernosus Muscle The ischiocavernosus muscle on each side covers the crus of the clitoris. Contraction of this muscle assists in causing the erection of the clitoris. Superficial Transverse Perineal Muscles The superficial transverse perineal muscles are identical in structure and function to those of the male. Nerve Supply All the muscles of the superficial perineal pouch are supplied by the perineal branch of the pudendal nerve. Perineal Body The perineal body is larger than that of the male and is clinically important. It is a wedge-shaped mass of fibrous tissue situated between the lower end of the vagina and the anal canal (Figs. 8-4 and 8-18). It is the point of attachment of many perineal muscles (as in the male), including the levatores ani muscles; the latter assist the perineal body in supporting the posterior wall of the vagina. Perineal Branch of Pudendal Nerve The perineal branch of the pudendal nerve on each side terminates in the superficial perineal pouch by supplying the muscles and skin (Fig. 8-8). Contents of the Deep Perineal Pouch in the Female The deep perineal pouch (Fig. 8-15) contains part of the urethra; part of the vagina; the sphincter urethrae, which is pierced by the urethra and the vagina; the deep transverse perineal muscles; the internal pudendal vessels and their branches; and the dorsal nerves of the clitoris. The urethra and the vagina are described in the next column. The sphincter urethrae and the deep transverse perineal muscles are described on page 406. The internal pudendal vessels and the dorsal nerves of the clitoris have an arrangement similar to the corresponding structures found in the male. A summary of the muscles of the perineum, their nerve supply, and their action is given in Table 8-1. Erection of the Clitoris Sexual excitement produces engorgement of the erectile tissue within the clitoris in exactly the same manner as in the male. Orgasm in the Female As in the male, vision, hearing, smell, touch, and other psychic stimuli gradually build up the intensity of sexual excitement. During this process the vaginal walls become moist because of transudation of fluid through the congested mucous membrane. In addition, the greater vestibular glands at the vaginal orifice secrete a lubricating mucus. The upper part of the vagina, which resides in the pelvic cavity, is supplied by the hypogastric plexuses and is sensitive only to stretch. The region of the vaginal orifice, the labia minora, and the clitoris are extremely sensitive to touch and are supplied by the ilioinguinal nerves and the dorsal nerves of the clitoris. Appropriate sexual stimulation of these sensitive areas, reinforced by afferent nervous impulses from the breasts and other regions, results in a climax of pleasurable sensory impulses reaching the central nervous system. Impulses then pass down the spinal cord to the sympathetic outflow (T1 to L2). The nervous impulses that pass to the genital organs are thought to leave the cord at the first and second lumbar segments in preganglionic sympathetic fibers. Many of these fibers synapse with postganglionic neurons in the first and second lumbar ganglia; other fibers may synapse in ganglia in the lower lumbar or pelvic parts of the sympathetic trunks. The postganglionic fibers are then distributed to the smooth muscle of the vaginal wall, which rhythmically contracts. In addition, nervous impulses travel in the pudendal nerve (S2, 3, and 4) to reach the bulbospongiosus and ischiocavernosus muscles, which also undergo rhythmic contraction. In many women, a single orgasm brings about sexual contentment, but other women require a series of orgasms to feel replete. Female Urethra The female urethra is about 1.5 in. (3.8 cm) long. It extends from the neck of the bladder to the external meatus, where it opens into the vestibule about 1 in. (2.5 cm) below the clitoris (Figs. 8-4 and 8-18). It traverses the sphincter urethrae and lies immediately in front of the vagina. At the sides of the external urethral meatus are the small openings of the ducts of the paraurethral glands. The urethra can be dilated relatively easily. Paraurethral Glands The paraurethral glands, which correspond to the prostate in the male, open into the vestibule by small ducts on either side of the urethral orifice (Fig. 8-19). Greater Vestibular Glands The greater vestibular glands are a pair of small mucus-secreting glands that lie under cover of the posterior parts of the bulb of the vestibule and the labia majora (Figs. 8-15 and 8-18). Each drains its secretion into the vestibule by a small duct, which opens into the groove between the hymen and the posterior part of the labium minus (Fig. 8-19). These glands secrete a lubricating mucus during sexual intercourse. Vagina Location and Description The vagina not only is the female genital canal but also serves as the excretory duct for the menstrual flow from the uterus and forms part of the birth canal. This muscular tube extends upward and backward between the vulva and the uterus (Fig. 8-4). It measures about 3 in. (8 cm) long. The cervix of the uterus pierces its anterior wall. The vaginal orifice in a virgin possesses a thin mucosal fold, P.410
called the hymen, which is perforated at its center. The upper half of the vagina lies above the pelvic floor within the pelvis between the bladder anteriorly and the rectum posteriorly; the lower half lies within the perineum between the urethra anteriorly and the anal canal posteriorly (Fig. 8-18).

Table 8-1 Muscles of Perineum
Muscle Origin Insertion Nerve Supply Action
External anal sphincter
Subcutaneous part Encircles anal canal, no bony attachments   Inferior rectal nerve and perineal branch of fourth sacral nerve Together with puborectalis muscle forms voluntary sphincter of anal canal
Superficial part Perineal body Coccyx
Deep part Encircles anal canal, no bony attachments
Puborectalis (part of levator ani) Pubic bones Sling around junction of rectum and anal canal Perineal branch of fourth sacral nerve and from perineal branch of pudendal nerve Together with external anal sphincter forms voluntary sphincter for anal canal
Male Urogenital Muscles
Bulbospongiosus Perineal body Fascia of bulb of penis and corpus spongiosum and cavernosum Perineal branch of pudendal nerve Compresses urethra and assists in erection of penis
Ischiocavernosus Ischial tuberosity Fascia covering corpus cavernosum Perineal branch of pudendal nerve Assists in erection of penis
Sphincter urethrae Pubic arch Surrounds urethra Perineal branch of pudendal nerve Voluntary sphincter of urethra
Superficial transverse perineal muscle Ischial tuberosity Perineal body Perineal branch of pudendal nerve Fixes perineal body
Deep transverse perineal muscle Ischial ramus Perineal body Perineal branch of pudendal nerve Fixes perineal body
Female Urogenital Muscles
Bulbospongiosus Perineal body Fascia of corpus cavernosum Perineal branch of pudendal nerve Sphincter of vagina and assists in erection of clitoris
Ischiocavernosus Ischial tuberosity Fascia covering corpus cavernosum Perineal branch of pudendal nerve Causes erection of clitoris
Sphincter urethrae Same as in male
Superficial transverse perineal muscle Same as in male
Deep transverse perineal muscle Same as in male

Supports of the Vagina

  • Upper third: Levatores ani muscles and transverse cervical, pubocervical, and sacrocervical ligaments
  • Middle third: Urogenital diaphragm
  • Lower third: Perineal body

Blood Supply Arteries The vaginal artery, a branch of the internal iliac artery, and the vaginal branch of the uterine artery supply the vagina. Veins Vaginal veins drain into the internal iliac veins. Lymph Drainage

  • Upper third: Internal and external iliac nodes
  • Middle third: Internal iliac nodes
  • Lower third: Superficial inguinal nodes

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Figure 8-19 A. Vulva. Note the different appearances of the hymen in a virgin (B), a woman who has had sexual intercourse (C), and a multiparous woman (D).

Nerve Supply The vagina is supplied by nerves from the inferior hypogastric plexuses. Vulva The term vulva is the collective name for the female external genitalia and includes the mons pubis, labia majora and minora, the clitoris, the vestibule of the vagina, the vestibular bulb, and the greater vestibular glands. Blood Supply Branches of the external and internal pudendal arteries on each side The skin of the vulva is drained into the medial group of superficial inguinal nodes. Lymph Drainage Medial group of superficial inguinal nodes Nerve Supply The anterior parts of the vulva are supplied by the ilioinguinal nerves and the genital branch of the genitofemoral nerves. The posterior parts of the vulva are supplied by the branches of the perineal nerves and the posterior cutaneous nerves of the thigh. P.412
Clinical Notes Vulval Infection In the region of the vulva, the presence of numerous glands and ducts opening onto the surface makes this area prone to infection. The sebaceous glands of the labia majora, the ducts of the greater vestibular glands, the vagina (with its indirect communication with the peritoneal cavity), the urethra, and the paraurethral glands can all become infected. The vagina itself has no glands and is lined with stratified squamous epithelium. Provided that the pH of its interior is kept low, it is capable of resisting infection to a remarkable degree. The Vulva and Pregnancy An important sign in the diagnosis of pregnancy is the appearance of a bluish discoloration of the vulva and vagina as a result of venous congestion. It appears at the 8th to 12th week and increases as the pregnancy progresses. Urethral Infection The short length of the female urethra predisposes to ascending infection; consequently, cystitis is more common in females than in males. Urethral Injuries Because of the short length of the urethra, injuries are rare. In fractures of the pelvis the urethra may be damaged by shearing forces as it emerges from the fixed urogenital diaphragm. Catheterization Because the female urethra is shorter, wider, and more dilatable, catheterization is much easier than in males. Moreover, the urethra is straight, and only minor resistance is felt as the catheter passes through the urethral sphincter. Vaginal Examination Digital examination of the vagina may provide the physician with much valuable information concerning the health of the vaginal walls, the uterus, and the surrounding structures (Fig. 8-4). Thus, the anatomic relations of the vagina must be known; they are considered in detail in Chapter 7. Injury to the Perineum During Childbirth The perineal body is a wedge of fibromuscular tissue that lies between the lower part of the vagina and the anal canal. It is held in position by the insertion of the perineal muscles and by the attachment of the levator ani muscles. In the female, it is a much larger structure than in the male, and it serves to support the posterior wall of the vagina. Damage by laceration during childbirth can be followed by permanent weakness of the pelvic floor. Few women escape some injury to the birth canal during delivery. In most, this is little more than an abrasion of the posterior vaginal wall. Spontaneous delivery of the child with the patient unattended can result in a severe tear of the lower third of the posterior wall of the vagina, the perineal body, and overlying skin. In severe tears, the lacerations may extend backward into the anal canal and damage the external sphincter. In these cases, it is imperative that an accurate repair of the walls of the anal canal, vagina, and perineal body be undertaken as soon as possible. In the management of childbirth, when it is obvious to the obstetrician that the perineum will tear before the baby’s head emerges through the vaginal orifice, a planned surgical incision is made through the perineal skin in a posterolateral direction to avoid the anal sphincters. This procedure is known as an episiotomy (Fig. 8-4). Breech deliveries and forceps deliveries are usually preceded by an episiotomy. Pudendal Nerve Block Area of Anesthesia The area anesthetized is the skin of the perineum; this nerve block does not, however, abolish sensation from the anterior part of the perineum, which is innervated by the ilioinguinal nerve and the genitofemoral nerve. Needless to say, it does not abolish pain from uterine contractions that ascend to the spinal cord via the sympathetic afferent nerves. Indications During the second stage of a difficult labor, when the presenting part of the fetus, usually the head, is descending through the vulva, forceps delivery and episiotomy may be necessary. Transvaginal Procedure The bony landmark used is the ischial spine (Fig. 8-20). The index finger is inserted through the vagina to palpate the ischial spine. The needle of the syringe is then passed through the vaginal mucous membrane toward the ischial spine. On passing through the sacrospinous ligament, the anesthetic solution is injected around the pudendal nerve (Fig. 8-20). Perineal Procedure The bony landmark is the ischial tuberosity (Fig. 8-20). The tuberosity is palpated subcutaneously through the buttock, and the needle is introduced into the pudendal canal along the medial side of the tuberosity. The canal lies about 1 in. (2.5 cm) deep to the free surface of the ischial tuberosity. The local anesthetic is then infiltrated around the pudendal nerve. P.413

Figure 8-20 Pudendal nerve block. 1, Transvaginal method. The needle is passed through the vaginal mucous membrane toward the ischial spine. After the needle is passed through the sacrospinous ligament, the anesthetic solution is injected around the pudendal nerve. 2, Perineal method. The ischial tuberosity is palpated subcutaneously through the buttock. The needle is inserted on the medial side of the ischial tuberosity to a depth of about 1 in. (2.5 cm) from the free surface of the tuberosity. The anesthetic is injected around the pudendal nerve.

Embryologic Notes Development of the External Genitalia Early in development, the embryonic mesenchyme grows around the cloacal membrane and causes the overlying ectoderm to be raised up to form three swellings. One swelling occurs between the cloacal membrane and the umbilical cord in the midline and is called the genital tubercle (Fig. 8-21). On each side of the membrane, another swelling, called the genital fold, appears. At the seventh week, the genital tubercle elongates to form the glans. The anterior part of the cloacal membrane, the urogenital membrane, now ruptures so that the urogenital sinus opens onto the surface. The entodermal cells of the urogenital sinus proliferate and grow into the root of the phallus, forming a urethral plate. Meanwhile, a second pair of lateral swellings, called the genital swellings, appears lateral to the genital folds. At this stage of development, the genitalia of the two sexes are identical. Male Genitalia In the male, the phallus now rapidly elongates and pulls the genital folds anteriorly onto its ventral surface so that they form the lateral edges of a groove, the urethral groove (Fig. 8-22). The floor of the groove is formed by the entodermal urethral plate. The penile urethra develops as the result of the two genital folds fusing together progressively along the shaft of the phallus to the root of the glans penis. During the fourth month, the remainder of the urethra in the glans is developed from a bud of ectodermal cells from the tip of the glans. This cord of cells later becomes canalized so that the penile urethra opens at the tip of the glans. The prepuce or foreskin is formed from a fold of skin at the base of the glans (Figs. 8-21 and 8-22). The fold of skin remains tethered to the ventral aspect of the root of the glans to form the frenulum. The erectile tissue—the corpus spongiosum and the corpora cavernosa—develops within the mesenchymal core of the penis. Female Genitalia The changes in the female are less extensive than those in the male. The phallus becomes bent and forms the clitoris (Fig. 8-21). The genital folds do not fuse to form the urethra, as in the male, but develop into the labia minora. The labia majora are formed by the enlargement of the genital swellings. Meatal Stenosis The external urinary meatus normally is the narrowest part of the male urethra, but occasionally the opening is excessively small and may cause back pressure effect on the entire urinary system. In severe cases, dilatation of the orifice by incision is necessary. Hypospadias Hypospadias is the most common congenital anomaly affecting the male urethra. The external meatus is situated on the ventral or undersurface of the penis anywhere between the glans and the perineum. Five degrees of severity may occur, the first of which is the most common: (1) glandular, (2) coronal, (3) penile, (4) penoscrotal, and (5) perineal (Fig. 8-23). In all except the first type, the penis is curved in a downward or ventral direction, a condition referred to as chordee. Types 1 and 2 are caused by a failure of the bud of ectodermal cells from the tip of the glans to grow into the substance of the glans and join the entodermal cells lining the penile urethra. Types 3, 4, and 5 are caused by a failure of the genital folds to unite on the undersurface of the developing penis and so convert the urethral groove into the penile urethra. In the penoscrotal variety, the genital swellings fail to fuse completely, so that the meatal orifice occurs in the midline of the scrotum. Type 1 requires no treatment; for the remainder, plastic surgery is necessary. Epispadias Epispadias is a relatively rare condition and is more commonly found in the male. In the male, the external meatus is situated on the dorsal or upper surface of the penis between the glans and the anterior abdominal wall (Fig. 8-24). The most severe type is associated with exstrophy of the bladder (see page 361). In the female, the urethra is split dorsally and is associated with a double clitoris. It is thought that epispadias is caused by failure of the embryonic mesenchyme to develop in the lower part of the anterior abdominal wall, so that when the cloacal membrane breaks down the urogenital sinus opens onto the surface of the cranial aspect of the penis. Plastic surgery is the required treatment P.414

Figure 8-21 The development of the external genitalia in the female and male.

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Figure 8-22 The development of the penile portion of the male urethra.

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Figure 8-23 Types of hypospadias: (1) glandular, (2) coronal, (3) penile, (4) penoscrotal, and (5) perineal. Ventral flexion (chordee) of the penis also is present.
Figure 8-24 Types of epispadias.
Figure 8-25 Cystourethrogram after intravenous injection of contrast medium (28-year-old man).

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Figure 8-26 The main features seen in the cystourethrogram shown in Figure 8-25.

Radiographic Anatomy The radiographic anatomy of the bones forming the boundaries of the perineum is shown in Figures 7-39, 7-41, and 7-43. A cystourethrogram of the male urethra is shown in Figures 8-25 and 8-26. Surface Anatomy The perineum when seen from below with the thighs abducted (Fig. 8-2) is diamond shaped and is bounded anteriorly by the symphysis pubis, posteriorly by the tip of the coccyx, and laterally by the ischial tuberosities. Symphysis Pubis The symphysis pubis is the cartilaginous joint that lies in the midline between the bodies of the pubic bones (Figs. 8-3, 8-27, and 8-28). It is felt as a solid structure beneath the skin in the midline at the lower extremity of the anterior abdominal wall. Coccyx The inferior surface and tip of the coccyx can be palpated in the cleft between the buttocks about 1 in. (2.5 cm) behind the anus (Fig. 8-3). P.418

Figure 8-27 Anterior view of the pelvis of a 27-year-old man.
Figure 8-28 Anterior view of the pelvis of a 29-year-old woman.

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Ischial Tuberosity The ischial tuberosity can be palpated in the lower part of the buttock (Fig. 8-3). In the standing position, the tuberosity is covered by the gluteus maximus. In the sitting position, the ischial tuberosity emerges from beneath the lower border of the gluteus maximus and supports the weight of the body. It is customary to divide the perineum into two triangles by joining the ischial tuberosities with an imaginary line (Fig. 8-2). The posterior triangle, which contains the anus, is called the anal triangle; the anterior triangle, which contains the urogenital orifices, is called the urogenital triangle. Anal Triangle Anus The anus is the lower opening of the anal canal and lies in the midline. In the living the anal margin is reddish brown and is puckered by the contraction of the external anal sphincter. Around the anal margin are coarse hairs (Fig. 8-29). Male Urogenital Triangle The male urogenital triangle contains the penis and the scrotum. Penis The penis consists of a root, a body, and a glans (Figs. 8-13, 8-16, and 8-27). The root of the penis consists of three masses of erectile tissue called the bulb of the penis and the right and left crura of the penis. The bulb can be felt on deep palpation in the midline of the perineum, posterior to the scrotum. The body of the penis is the free portion of the penis, which is suspended from the symphysis pubis. Note that the dorsal surface (anterior surface of the flaccid organ) usually possesses a superficial dorsal vein in the midline (Figs. 8-13). The glans penis forms the extremity of the body of the penis (Figs. 8-13, 8-16, and 8-27). At the summit of the glans is the external urethral meatus. Extending from the lower margin of the external meatus is a fold connecting the glans to the prepuce called the frenulum. The edge of the base of the glans is called the corona (Fig. 8-16). The prepuce or foreskin is formed by a fold of skin attached to the neck of the penis. The prepuce covers the glans for a variable extent, and it should be possible to retract it over the glans. Scrotum The scrotum is a sac of skin and fascia (Figs. 8-12 and 8-27) containing the testes and the epididymides. The skin of the scrotum is rugose and is covered with sparse hairs. The bilateral origin of the scrotum is indicated by the presence of a dark line in the midline, called the scrotal raphe, along the line of fusion. Testes The testes should be palpated. They are oval shaped and have a firm consistency. They lie free within the tunica vaginalis (see Fig. 4-21) and are not tethered to the subcutaneous tissue or skin. Epididymides Each epididymis can be palpated on the posterolateral surface of the testis. The epididymis is a long, narrow, firm structure having an expanded upper end or head, a body, and a pointed tail inferiorly (see Fig. 4-21). The cordlike vas deferens emerges from the tail and ascends medial to the epididymis to enter the spermatic cord at the upper end of the scrotum. Female Urogenital Triangle Vulva Vulva is the term applied to the female external genitalia (Figs. 8-19, 8-28, and 8-29). Mons Pubis The mons pubis is the rounded, hair-bearing elevation of skin found anterior to the pubis (Figs. 8-19 and 8-28). The pubic hair in the female has an abrupt horizontal superior margin, whereas in the male it extends upward to the umbilicus. Labia Majora The labia majora are prominent, hair-bearing folds of skin extending posteriorly from the mons pubis to unite posteriorly in the midline (Figs. 8-19 and 8-29). Labia Minora The labia minora are two smaller, hairless folds of soft skin that lie between the labia majora (Fig. 8-19). Their posterior ends are united to form a sharp fold, the fourchette. Anteriorly, they split to enclose the clitoris, forming an anterior prepuce and a posterior frenulum (Figs. 8-19 and 8-29). Vestibule The vestibule is a smooth triangular area bounded laterally by the labia minora, with the clitoris at its apex and the fourchette at its base (Figs. 8-19 and 8-29). Vaginal Orifice The vaginal orifice is protected in virgins by a thin mucosal fold called the hymen, which is perforated at its center (Fig. 8-19). At the first coitus, the hymen tears, usually posteriorly or posterolaterally, and after childbirth only a few tags of the hymen remain (Fig. 8-19). Orifices of the Ducts of the Greater Vestibular Glands Small orifices, one on each side, are found in the groove between the hymen and the posterior part of the labium minus (Fig. 8-19). Clitoris This is situated at the apex of the vestibule anteriorly (Fig. 8-19). The glans of the clitoris is partly hidden by the prepuce (Fig. 8-29). P.420

Figure 8-29 The perineum in a 25-year-old woman, inferior view. A. With labia together. B. With labia separated.

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Clinical Problem Solving Read the following case histories and select the best answer to the question following them. A 53-year-old man complained that for the past 4 years he had frequently passed blood-stained stools. Recently, he had noticed that his “bowel” protruded from his anus after defecation, and this caused him considerable discomfort. 1. The following symptoms and signs in this patient were consistent with a diagnosis of third-degree internal hemorrhoids except which? (a) The patient suffered from intense perianal irritation caused by the mucous secretions from the prolapsed mucous membrane. (b) Proctoscopic examination revealed three pink swellings of mucous membrane at the level of the anal valves. (c) The swellings were situated at 1, 4, and 9 o’clock with the patient in the lithotomy position. (d) The swellings bulged downward when the patient was asked to strain. (e) Large, congested veins were seen in the swellings. (f) The swellings remained outside the anus after defecation. (g) Abrasion of the mucous membrane was responsible for the bleeding. View Answer1. C. The swellings of internal hemorrhoids are situated at 3, 7, and 11 o’clock with the patient in the lithotomy position. These swellings are caused by a dilatation of the three main tributaries of the superior rectal vein. A 42-year-old woman visited her physician because she experienced an agonizing pain in the rectum, which occurred on defecation. She had first noticed the pain a week before when she tried to defecate. The pain lasted for about an hour, then passed off, only to return with the next bowel movement. She said that she suffered from constipation and admitted that sometimes her stools were streaked with blood. After a careful examination, a diagnosis of anal fissure was made. 2. The following statements concerning this case are correct except which? (a) Examination of the anal canal was difficult because any attempt to insert a gloved finger into the canal caused severe pain. (b) The anus was kept tightly closed by the spasm of the external anal sphincter. (c) Gentle eversion of the anal margin under local anesthesia revealed the lower edge of a linear tear in the posterior wall of the anal canal; a small tag of skin projected from the lower end of the tear. (d) The forward edge of a hard fecal mass may have caught one of the anal valves and torn it downward as it descended. (e) Anal fissures tend to occur on the anterior and posterior walls of the anal canal because the mucous membrane is poorly supported in this region by the superficial external sphincter muscle. (f) The mucous membrane of the lower half of the anal canal is innervated by autonomic afferent nerves and is sensitive only to stretch. View Answer2. F. The mucous membrane of the lower half of the anal canal is innervated by the inferior rectal nerve and is very sensitive to pain, temperature, touch, and pressure. A 16-year-old boy was taking part in a bicycle race when, on approaching a steep hill, he stood up on the pedals to increase the speed. His right foot slipped off the pedal and he fell violently, his perineum hitting the bar of the bicycle. Several hours later he was admitted to the hospital unable to micturate. On examination, he was found to have extensive swelling of the penis and scrotum. A diagnosis of ruptured urethra was made. 3. The following statements concerning this case are correct except which? (a) Rupture of the bulbous part of the urethra had taken place. (b) The urine had escaped from the urethra and extravasated into the superficial perineal pouch. (c) The urine had passed forward over the scrotum and penis to enter the anterior abdominal wall. (d) The urine had extended posteriorly into the ischiorectal fossae. (e) The urine was located beneath the membranous layer of superficial fascia. View Answer3. D. The superficial perineal pouch is closed off posteriorly by the attachment of the membranous layer of superficial fascia to the posterior margin of the urogenital diaphragm. Because of this attachment the extravasated urine cannot enter the ischiorectal fossae. A 34-year-old man was suffering from postoperative retention of urine after an appendectomy. The patient’s urinary tract was otherwise normal. Because the patient was in considerable discomfort, the resident decided to pass a catheter. 4. The following statements concerning the catheterization of a male patient are correct except which? (a) Because the external urethral orifice is the narrowest part of the urethra, once the tip of the catheter has passed this point, the further passage should be easy. (b) Near the posterior end of the fossa terminalis, a fold of mucous membrane projects from the roof and may catch the end of the catheter. (c) The membranous part of the urethra is narrow and fixed and may produce some resistance to the passage of the catheter. (d) The prostatic part of the urethra is the widest and most easily dilated part of the urethra and should cause no difficulty to the passage of the catheter. (e) The bladder neck is surrounded by the sphincter vesicae and always strongly resists the passage of the tip of the catheter. View Answer4. E. The bladder neck does not cause obstruction to the passage of the catheter. In this patient, the sphincter may provide some minor resistance that is easily overcome. A 41-year-old woman was seen in the emergency department complaining of a painful swelling in the region of the anus. On examination, a hot, red, tender swelling was found on the right side of the anal margin. A diagnosis of ischiorectal abscess was made. 5. The following statements concerning this case are probably correct except which? (a) An ischiorectal abscess is a common complication of anal fissure. (b) The fat in the ischiorectal fossa is prone to infection that might extend laterally through the base of the anal fissure. (c) The fat in the ischiorectal fossa has a profuse blood supply. (d) A surgical incision of the abscess should provide adequate drainage of the pus. (e) The surgeon should avoid the inferior rectal nerve and vessels that cross the ischiorectal fossa from the lateral to the medial side. View Answer5. C. The fat in the ischiorectal fossa has a poor blood supply. A 35-year-old woman was seen by her obstetrician and gynecologist complaining of a swelling in the genital region. On examination, a tense cystic swelling was found beneath the posterior two thirds of the right labium majus and minus. A diagnosis of a cyst of the right greater vestibular gland (Bartholin’s cyst) was made. 6. The following statements concerning this case are probably correct except which? (a) The cyst of the greater vestibular gland is produced by the retention of secretion caused by the blockage of the duct. (b) Infection of the duct by the gonococcus is a common cause of the blockage. (c) Infection of the cyst may occur, forming a painful abscess. (d) The lymphatic drainage of this area is into the lateral group of superficial inguinal nodes. (e) A small tender swelling was detected below and medial to the inguinal ligament. View Answer6. D. The lymphatic drainage of this area is into the medial group of superficial inguinal nodes situated below the inguinal ligament. The spread of infection can result in an enlargement of one of the nodes, as in this case, which becomes tender to palpation. P.422
Review Questions Multiple-Choice Questions Select the best answer for each question. 1. The following statements concerning the female urethra are correct except which? (a) It lies immediately anterior to the vagina. (b) Its external orifice lies about 2 in. (5 cm) from the clitoris. (c) It is about 1.5 in. (3.75 cm) long. (d) It pierces the urogenital diaphragm. (e) It is straight, and only minor resistance is felt as a catheter is passed through the urethral sphincter. View Answer1. B. The female urethra opens into the vestibule at the external meatus about 1 in. (2.5 cm) below the clitoris. 2. The following structures can be palpated by a vaginal examination except which? (a) Sigmoid colon (b) Ureters (c) Perineal body (d) Ischial spines (e) Iliopectineal line View Answer2. E. The iliopectineal line lies at the brim of the bony pelvis and is far beyond the reach of a vaginal examination. 3. The following statements concerning the ischiorectal fossa are correct except which? (a) The pudendal nerve lies in its lateral wall. (b) The floor is formed by the superficial fascia and skin. (c) The lateral wall is formed by the obturator internus muscle and its fascia. (d) The medial wall is formed in part by the levator ani muscles. (e) The roof is formed by the urogenital diaphragm. View Answer3. E. The roof of the ischiorectal fossa is formed by the junction of the medial and lateral walls. The medial wall is formed by the sloping levator ani muscle, and the anal canal and the lateral wall are formed by the lower part of the obturator internus muscle, covered with pelvic fascia. 4. The following statements concerning the penis are correct except which? (a) Its root is formed in the midline by the bulb of the penis, which continues anteriorly as the corpus spongiosum. (b) Its roots laterally are formed by the crura, which continue anteriorly as the corpora cavernosa. (c) The penile urethra lies within the corpus spongiosum. (d) The glans penis is a distal expansion of the fused corpora cavernosa. (e) The penis is suspended from the lower part of the anterior abdominal wall by two condensations of deep fascia. View Answer4. D. The glans penis is a distal expansion of the corpus spongiosum. 5. The following statements concerning perineal structures are correct except which? (a) The anorectal ring is formed by the subcutaneous, superficial, and deep fibers of the external anal sphincter. (b) The urogenital diaphragm is attached laterally to the inferior ramus of the pubis and the ischial ramus. (c) The bulbourethral glands are situated in the deep perineal pouch. (d) The anococcygeal body is rarely damaged in childbirth. (e) The lymph drainage of the skin around the anus is into the medial group of superficial inguinal nodes. View Answer5. A. At the junction of the rectum and anal canal, the internal sphincter, the deep part of the external sphincter, and the puborectalis muscles form a distinct ring, called the anorectal ring. 6. The urogenital diaphragm is formed by the following structures except which? (a) Deep transverse perineal muscle (b) Perineal membrane (c) Sphincter urethrae (d) Colles’ fascia (membranous layer of superficial fascia) (e) Parietal pelvic fascia covering the upper surface of the sphincter urethrae muscle View Answer6. D. Colles’ fascia (membranous layer of superficial fascia) takes no part in the formation of the urogenital diaphragm; it is too superficial and lies just beneath the skin. 7. In the male, the following structures can be palpated on rectal examination except which? (a) Bulb of the penis (b) Urogenital diaphragm (c) Anorectal ring (d) The anterior surface of the sacrum (e) Ureter View Answer7. E. The ureters cannot be felt on rectal examination in both sexes. An abnormal ureter, thickened by disease, can be felt on vaginal examination. 8. The following statements concerning the anal canal are correct except which? (a) It is about 1.5 in. (3.8 cm) long. (b) It pierces the urogenital diaphragm. (c) It is related laterally to the external anal sphincter. (d) It is the site of an important portal–systemic anastomosis. (e) The mucous membrane of the lower half receives its arterial supply from the inferior rectal artery. View Answer8. B. The anal canal lies posterior to the urogenital diaphragm and, therefore, does not pierce it. 9. The following statements concerning the subcutaneous part of the external anal sphincter are correct except which? (a) It encircles the anal canal. (b) It is not attached to the anococcygeal body. (c) It is composed of striated muscle fibers. (d) It is not responsible for causing the anal canal and rectum to join at an acute angle. (e) It is innervated by the middle rectal nerve. View Answer9. E. The subcutaneous part of the external anal sphincter is innervated by the inferior rectal nerve, which is a branch of the pudendal nerve. 10. The following statements concerning defecation are correct except which? (a) The act is often preceded by the entrance of feces into the rectum, which gives rise to the desire to defecate. (b) The muscles of the anterior abdominal wall contract. (c) The external anal sphincters and the puborectalis relax. (d) The internal sphincter contracts and causes the evacuation of the feces. (e) The mucous membrane of the lower part of the anal canal is extruded through the anus ahead of the fecal mass. View Answer10. D. The internal anal sphincter is relaxed during defecation. 11. The process of ejaculation depends on the followingprocesses except which? (a) The sphincter of the bladder contracts. (b) The sympathetic preganglionic nerve fibers arising from the first and second lumbar segments of the spinal cord must be intact. (c) The smooth muscle of the epididymis, ductus (vas) deferens, seminal vesicles, and prostate contracts. (d) The bulbourethral glands and the urethral glands are active. (e) The bulbospongiosus muscles relax. View Answer11. E. During ejaculation, the bulbospongiosus muscles rhythmically contract and compress the urethra, forcing the seminal fluid out of the external meatus. 12. The following structures receive innervation from branches of the pudendal nerve except which? (a) Labia minora (b) Urethral sphincter (c) The posterior fornix of the vagina (d) Ischiocavernosus muscles (e) Skin of the penis or clitoris View Answer12. C. The posterior fornix of the vagina is innervated by the inferior hypogastric plexuses. Read the case history and select the best answer to the questions following it. While bathing her 5-month-old boy, a mother noticed that his penis tended to curve downward. She decided to seek advice from a pediatrician. 13. The pediatrician examined the child and made the following possible correct observations and statements except which? (a) The penis had a definite downward curvature (chordee). (b) Both testes were in the scrotum. (c) The external urethral meatus opened halfway along the undersurface of the penis. (d) The fusion of the genital folds on the ventral or undersurface of the shaft of the penis was incomplete so that the urethra opened on the ventral surface. (e) The condition is a rare congenital anomaly. View Answer13. E. The clinical condition is one of the commonest congenital anomalies affecting the male urethra. 14. The pediatrician made the following possible correct statements to the mother regarding the diagnosis and treatment except which? (a) The child has hypospadias associated with chordee. (b) The proximal portion of the penile urethra had developed normally but was incomplete. (c) The bud of cells (ectodermal) on the tip of the glans penis had failed to grow into the substance of the glans and join up with the cells (entodermal cells) of the penile urethra. (d) The treatment is the surgical correction of the chordee, which is followed by the plastic reconstruction of the penile urethra. (e) In view of the delicate tissues involved, the treatment should be delayed until the child is at least 10 years old. View Answer14. E. The surgical treatment should start at about the age of 2 years and be complete before the child goes to school. Little boys like to look the same as other little boys.

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