MUCOUS MEMBRANE OF THE NASAL FOSSAE. 



139 



they are small and thinly scattered, and both the hairs and glands are absent near 

 the posterior limit of the vestibule, which is marked off by a curved prominence 

 (limen restibuli) from the nasal fossae proper. At this line the stratified epithelium 

 of the vestibule passes into the ciliated epithelium of the fossae, and the cutaneous 

 glands are replaced by compound mucous glands. At the front of the vestibule, 

 enclosed by the curved cartilage of the aperture, is a shallow cul-de-sac known as the 

 ventricle of the nares. 



MUCOUS MEMBRANE. 



The pituitary or Schneiderian membrane, which lines the cavities of the nose, is 

 a highly vascular mucous membrane, inseparably united with the periosteum and 

 perichondrium over which it lies. It is continuous with the skin through the 

 nostrils ; with the mucous membrane of the pharynx through the posterior nares ; 

 with the conjunctiva through the nasal duct and lachrymal canaliculi ; and with 

 the lining membrane of the several sinuses which communicate with the nasal fossae. 



upper 

 lateral 



cartilage 



of 

 cartilage aperture 



sphenoidal antrum 



ost. border of septum 



Eustachian aperture 

 salpingo-phar. fold 



soft palate 



nasal septui 



Fig. 157. VlBW OF THE SEPTUM NASI FROM THE RIGHT SIDE. 



vestibule 



The pituitary membrane, however, varies much in thickness and vascularity in 

 different parts. It is thickest and most vascular over the turbinate bones 

 (particularly the inferior) and on the septum nasi it is also very thick and spongy ; 

 but in the intervals between the turbiiiate bones, and over the floor of the nasal 

 fossae, it is considerably thinner. In the maxillary, frontal, and sphenoidal sinuses, 

 and in the ethmoidal cells, the lining mucous membrane is very thin and pale, and 

 contrasts strongly with that which lines the nasal fossae. 



The character of the epithelium varies in different parts, and by this, in a general 

 way, three regions of the nasal fossae may be distinguished. Thus, the region of 

 the external nostrils (the vestibule) is lined with stratified squamous epithelium ; 



