384 



CIRCULATION AND RESPIRATION 



Tongue 



Trachea 



Esophagui 



and the bronchial tubes. All of these are lined with 



mucous membrane. In the nostrils (Fig. 288) the mucous 



membrane is spread 

 out over a large sur- 

 face, arid secretes a 

 great deal of mucus. 

 The nostrils, because 

 of their length, serve 

 to warm the air before 

 it reaches the wind- 

 pipe and lungs. The 

 mucus which they 

 secrete makes them 

 moist, and catches the 

 dust particles that are 

 in the inhaled air. 

 The air passages are 

 also lined, almost 



everywhere, with cilia (cf. 333); these sweep back the 



dust particles. 



The pharynx was described in 361. It is separated 



from the nostrils, when we swallow food, by the "soft 



palate." The two tonsils are in the sides of the pharynx, 



under the lower jaw bone. 



388. The Larynx and Trachea. The larynx (Fig. 

 289) is a box made out of pieces of cartilage placed at the 

 upper end of the trachea (windpipe). When we swallow, 

 the larynx is drawn upward against its cover, the epi- 

 glottis (cf. 361, Fig. 280) ; food passes over it in going to 

 the esophagus. We can feel one of the larynx cartilages 



FIG. 288. 

 The Mouth and the Nasal Cavity. 



