194 



APPLIED PHYSIOLOGY 



makes an extra exertion and becomes short of breath, the air irritates 

 the throat and brings on a cough. 



With many, mouth breathing is a habit which can easily be broken 

 by attention to the breathing. In others, it' is due to a cold, or to ade- 

 noid vegetations, or to enlarged tonsils. 



334. The larynx. In the front side of the lower part 

 of the pharynx is the opening of a box called the larynx, 

 through which air passes. The larynx is a box of carti- 



A slice from the trachea (x 200). 



a cartilage. b glands in the mucous membrane. 



c lining of epithelial cells. 



d cilia upon the surface of the epithelium. 



lage. Across its upper end are stretched two thin elastic 

 bands, the vocal cords, which can be tightened and brought 

 near together at will. Air passing between them produces 

 a sound called the voice. 



335. The trachea. From the bottom of the larynx 

 there extends downward a tube called the windpipe or 

 trachea. The trachea is about four and one half inches 

 in length and three quarters of an inch in diameter. It 

 is composed of a framework of twenty hoops of cartilage, 



