1072 



ORGANS OF SPECIAL SENSE 



nasal fossa, situated between the dorsal extremities of the middle and inferior concha 

 (turbinate bones) and the anterior lip of the pharyngeal orifice of the tuba auditiva 

 (Eustachian tube), is known as the naso-pharyngeal meatus. 



The nasal mucous membrane (the pituitary or Schneiderian membrane). The 

 nasal cavity is completely lined with mucous membrane, which ventrally, at the 

 limen, blends with the skin which lines this part of the vestibule (p. 1070). Dorsally 

 it joins the mucous membrane of the pharynx and palate. It covers up some of 

 the openings which are seen in the bony walls; those, however, which lead into the 

 air-sinuses and into the naso-lachrymal duct remain patent, although the bony open- 

 ings are much reduced in size. In the nasal cavity proper the bright rose-red vascu- 

 lar mucous membrane is tightly bound to the periosteum and perichondrium, and 

 is covered with a ciliated columnar epithelium. Numerous large mucous nasal 

 glands pour their more or less watery secretion over the entire surface, and form 

 in the submucous stratum a layer of considerable thickness. Here, also, a very con- 

 siderable venous plexus is found, especially over the middle and inferior conchas (tur- 



FIG. 770. TRANSVERSE SECTION THROUGH THE NASAL Fosses AND MAXILLARY SINUS AT 

 THE DORSAL EXTREMITY OF THE MIDDLE CONCHA. (Ventral view.) 



binate bones), where it forms the cavernous plexus of the conchse. The thickness 

 which these glands and venous plexuses give to the mucous membrane causes the 

 air-spaces of the bony fossse to be much contracted in the recent state, and in children 

 a considerable amount of adenoid tissue is also found in the submucous layer. The 

 region covered by the mucous membrane just described forms the greater part of 

 the nasal cavity, and is known as the respiratory region. A small area of the mucous 

 membrane over the superior concha and the adjacent septal wall (fig. 772) has a some- 

 what different structure. In this area the olfactory nerves terminate, whence it is 

 known as the olfactory region, and its mucous membrane, compared with that of 

 the respiratory region, is less vascular, yellow or yellowish-brown in colour, and covered 

 by a non-ciliated epithelium. It contains specially modified cells, which form the 

 true olfactory organ and receive the terminations of the olfactory nerve. Small 

 mucous olfactory glands occur in the region. The paranasal sinuses or accessory 

 cavities which connect with the nasal cavity are: the maxillary sinuses (antra of 

 Highmore), the sphenoidal sinuses, the frontal sinuses, and the ethmoidal cells, 

 and have been described in the section on OSTEOLOGY. The mucous membrane 



