THE VENTILATING SYSTEM OF THE BODY 269 



These rings may be felt from the outside of the throat just 

 below the larynx or " Adam's apple. " The trachea divides into 

 two tubes or bronchi, one of which goes to each lung. In 

 the lungs the bronchi are divided into many smaller tubes 

 which finally end in the air chambers of the lungs. The tra- 

 chea, bronchi and some other parts of the air passages are 



FIG. 93. Human larynx, trachea* bronchi, and lungs; showing the ramifica- 

 tion of the bronchi, and the division of the lungs into lobules. (Brubaker.) 



lined with ciliated cells whose whip-like projections catch 

 any dust that may be breathed in and gradually push it toward 

 the throat, where it is swallowed. The esophagus, the tube 

 through which food reaches the stomach, lies directly behind 

 the trachea and all food therefore passes across the opening 

 from the throat into the trachea. It is prevented from 

 getting into the trachea by a spoon-shaped bridge, the epi- 



