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The medial wall of each nasal cavity is the nasal septum, a thin sheet of bone (posteriorly) and cartilage (anteriorly), that lies between the roof and floor of the cavity (Fig. 32.2D).

Bony septum

The septum is usually relatively featureless but sometimes exhibits ridges or bony spurs. The posterosuperior part of the septum and its posterior border are formed by the vomer, which extends from the body of the sphenoid to the hard palate (for more details, see Chapter 29). Its surface is grooved by the nasopalatine nerves and vessels. The anterosuperior part of the septum is formed by the perpendicular plate of the ethmoid which is continuous above with the cribriform plate. Other bones which make minor contributions to the septum at the upper and lower limits of the medial wall are the nasal bones and the nasal spine of the frontal bones (anterosuperior), the rostrum and crest of the sphenoid (posterosuperior), and the nasal crests of the maxilla and palatine bones (inferior).

Cartilaginous septum

The septal cartilage is almost quadrilateral and may extend back (especially in children) for some distance between the vomer and the perpendicular plate of the ethmoid. Its anterosuperior margin is connected above to the posterior border of the internasal suture, and the distal end of its superior portion is continuous with the upper lateral cartilages. The anteroinferior border is connected by fibrous tissue on each side to the medial crurae of the major alar cartilage. The posterosuperior border joins the perpendicular plate of the ethmoid, while the posteroinferior border is attached to the vomer and anterior to that to the nasal crest and anterior nasal spine of the maxilla. The anteroinferior part of the nasal septum between the nares is devoid of cartilage and is therefore called the membranous septum: it is continuous with the columella anteriorly.

Above the incisive canals, at the lower edge of the septal cartilage, a depression pointing downwards and forwards is all that remains of the nasopalatine canal which connected the nasal and buccal cavities in early fetal life. Near this recess, a minute orifice leads back into a blind tubule, 2–6 mm long, which lies on each side of the septum and houses remnants of the vomeronasal organ.

Vomeronasal organ

In most amphibia, reptiles and mammals, the vomeronasal organ is the peripheral sensory organ of the accessory olfactory system. In these animals, paired vomeronasal organs are located either at the base of the nasal septum or in the roof of the mouth, and are involved in chemical communication that often, but not exclusively, is mediated via pheromones. In many macrosomatic animals the vomeronasal organ consists of a vomeronasal duct which contains chemosensory cells, and a vomeronasal nerve which terminates in the accessory olfactory bulb in the CNS. Whether adult humans possess a vomeronasal organ remains controversial; it is claimed that the duct sometimes persists beyond the embryonic stage (for detailed reviews, see Meredith 2001, Witt & Hummel 2006) but no neural connection appears to be present in humans after birth.

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