A STUDY OF RESPIRATION 211 



windpipe divides into two tubes, the right and left bron'chus, 

 each of which supplies air to one lung (see Figs. 98 and 99). 



FIG. 98. The Windpipe and its Brandies (dorsal view). 



Ao = aorta. M = opening from mouth. 



Br = bronchi. PA = pulmonary artery. 



D = diaphragm. P V = pulmonary vein. 



Gl = glottis opening. RL = right lung. 



H= heart. Tr = trachea (windpipe). 



LL = left lung. V.C.L. = inferior vena cava. 



Within the lungs, the bronchi branch off into a vast num- 

 ber of very small pipes, called bron'chi-al tubes. The finest 

 divisions of these pipes open into extremely thin-walled air 

 so.es (Figs. 99 and 103). 



The Nose Cavity. The openings into the nose cavity are 

 guarded by a forest of projecting hairs, through which the 

 air is strained. By this provision a considerable amount 

 of dust is kept from entering the body. The nose itself is 

 lined by mucous membrane which covers the vomer, the up- 

 per surface of the hard palate, and the spongy bones which 

 project from the lateral walls of the nose chambers. Its mu- 



