280 



HUMAN PHYSIOLOGY 



nose. The nasal passages occupy a large space in the 

 skull and are extensively subdivided. Scroll-like proc- 

 esses from their walls jut into them and present a 

 much greater surface to the passing air than would 

 be supposed. These processes consist of a bony founda- 

 tion overlaid with mucous membrane. The blood- 

 supply of the lining of the nose is a liberal one and the 

 cells are constantly secreting moisture. As the air is 



FIG. 68. The path of the breath. Details of the upper part may 

 be seen to better advantage in Fig. 43. n, Nasal passage; p, pharynx; 

 Z, larynx; t, trachea; b, left bronchus; e, esophagus, continuous with 

 the pharynx above. 



inhaled it is affected in at least three ways by its contact 

 with the mucous membrane. 



In the first place, it deposits a large proportion of 

 the dust particles which it may have brought in. As 

 has been stated in Chapter IV, such particles are removed 

 by ciliary motion whether toward the pharynx or the 

 nostrils is disputed. In the second place, the air which 

 is usually taken in at a temperature below that of the 

 body is warmed nearly to blood heat in passing through 



