572 THE TISSUES. 



CHAPTEE XVI. 



THE RESPIRATORY ORGANS. 



THE respiratory apparatus consists of the nasal passages ; the 

 upper part of the pharynx; the larynx; the trachea; and the lungs. 

 The mucous membrane lining all these constitutes the air-passages. 



1. The mucous membrane alone of the nasal passages, needs to 

 be described here. It is continuous with the skin of the nose at 

 the entrance of the nostrils, and with the mucous membrane of the 

 eye through the lachrymal passages. It is intimately connected 

 with the periosteum of the nasal passages, in the sinuses and some 

 other parts; but on the spongy bones and the septum, forming the 

 direct passages to the pharynx, it is thicker, having a submucous 

 layer of areolar tissue containing plexuses both of arteries and 

 veins. The corium presents papillae resembling those of the skin, 

 just within the nostrils. Its epithelium is of the compound scaly 

 variety, like that of the skin, to the distance of about f of an inch 

 within the nostrils, where it becomes the compound conoidal cili- 

 ated epithelium, there being two layers of cells (Fig. 400) ; and 



Section of the ciliated epithelium of the nasal passages, a. Superficial cells clothed with cilia. 

 b. Deeper series becoming elongated vertically, c. Various shapes of the perfect ciliated cells. 

 (Magnified 180 diameters.) 



thus continues through the nasal passages, except over the olfac- 

 tory region (p. 449). The same epithelium also extends over the 

 upper portion of the pharynx, posteriorly to the level of the larynx, 

 and in front over the posterior surface of the velum this portion 

 constituting a part of the air-passages, as already stated (p. 522). 



