THE TRACHEA 167 



surface of warm moist membrane over which the air 

 must pass. 



Trachea. The windpipe, or trachea, begins at the 

 lower end of the pharynx, that wide shallow chamber 

 at the back of the mouth into which both nose and mouth 

 open. The trachea lies in front of the esophagus and 

 is shut off from it by a lid, which closes during swallow- 

 ing to keep out particles of food. It is an elastic tube 

 with hoops of cartilage in its walls. The ends of these 

 hoops do not quite meet and tend constantly to spring 

 apart. As a result, the trachea is held widely open 

 so that the air can always pass through it easily. 



Larynx. As in every other part of the body each 

 mechanism is made to serve as many purposes as possi- 

 ble, so in the trachea we find the passage of air through 

 it used for the production of voice. A special chamber, 

 the walls of which are stiffened with cartilage, lies near 

 the top of the trachea. It has two membranes which can 

 be made to stretch tightly across the air passage, so as 

 to meet at their edges and shut off the air. When the 

 air passes between their edges, these membranes vibrate 

 and thereby produce sounds which constitute the voice. 1 

 This chamber is called the larynx and causes the promi- 

 nence in the throat known as "Adam's Apple." 



Bronchial tubes. At its lower end near the heart, 

 the trachea divides into two short branches, the bronchi, 

 one of which goes toward the right side of the chest, 

 the other toward the left, to connect respectively with 

 the right and left lung. The bronchi are equipped with 

 cartilaginous hoops to keep them open. Upon entering 

 the lungs, they at once multiply into an immense number 

 of smaller branches, the bronchial tubes, which in turn di- 

 vide into smaller ones and thus penetrate to every part of 



1 See p. 276. 



