272 



ANIMAL BIOLOGY 



are caught and prevented from interfering with respira- 

 tion. Posteriorly the nasal cavity leads to a space called 

 the pharynx; at the lower end of this is a cartilaginous box, 



PIG. 200. Vocal cords, a, closed; b, open. 



the larynx,' which you can feel in the front part of your 

 throat (Adam's apple). The opening of the larynx lies 

 just in front of the opening of the esophagus, but it may 

 be covered by a fleshy lid, the epiglottis, which normally 



closes it during the act of 

 swallowing. Sometimes food 

 "goes down the wrong way" 

 when it sets up the act of cough- 

 ing by which it is usually ex- 

 pelled. 



The larynx contains the 

 vocal cords whose function it 

 is to produce the voice, and it 

 leads below to a tube called the 

 trachea or windpipe through 

 which air passes to the lungs. 

 The trachea is furnished with 

 a series of C-shaped cartilages 



7 



or nearly complete rings which 

 keep its walls from collapsing 



and thus impeding the passage of air. The inner lining 

 consists of mucous membrane containing many cells with 

 fine cilia whose constant beating creates a current toward 



F i G ' 



windpipe *B with its branches 



r, bronchial tubes. 



