94 PHYSIOLOGY AND TEMPERANCE. 



branch divides into a number of smaller ones, like the 

 branches "of a tree, until they terminate in the delicate air- 

 cells just described. 



The windpipe is a hollow tube, about four to five inches 

 long, made up of fibrous tissue in which are situated rings of 

 cartilage. These rings are not quite perfect, but more like a 

 horseshoe in shape, being incomplete at the back. They are 

 easily felt in front. If the rings were complete at the back, 

 the gullet could not expand so readily when we swallow food 

 The presence of cartilage in the tube 

 prevents the sides from coming together 

 by the suction of air. It also protects 

 the passage from any outside pressure. 



Where it enters the chest the wind- 

 pipe divides into the right and left bron- 

 chial tubes. At the root of the lung 

 each tube divides and subdivides, until 

 it spreads throughout the entire organ. 



The larynx is a triangular-shaped box 

 of cartilage situated at the top of the 

 windpipe. The cartilage projects for- 



Fio. 31. Front view of the 



Larynx: i, upper ring of ward, especially in the male, in whom 

 windpipe; 2, 3, cartilage of ft ^ s usua lly' quite prominent. This is 



the larynx (figure 3 is on the 



Adam's apple); 4, epiglottis; commonly called " Adam s apple." The 

 M, membrane uniting car- larynx has been called the voice box, 

 because here the various sounds of the 

 human voice are produced. 



The entrance to the larynx is a triangular opening at the 

 root of the tongue, called the glottis, and this entrance is 

 guarded by the epiglottis, which was mentioned in connection 

 with the pharynx. Within the larynx, on each side, the 

 lining membrane forms two folds, stretching from front to 

 back, and separated by a well-marked hollow. These are 

 the vocal cords. The lower folds are strengthened by fibrous 



