178 



ADVANCED PHYSIOLOGY 



These rings are not complete but are in the form of irregular 

 horseshoes with the open part behind, where the windpipe 

 comes next to the oesophagus. The windpipe is, therefore, 



soft and flexible next to the 

 oesphagus so that the swal- 

 lowing of food through the 

 latter is not hindered. As 

 long as the larynx is open 

 and the epiglottis is raised, 

 air drawn in either through 

 the nostrils or the mouth 

 passes with perfect freedom 

 down the windpipe into the 

 lungs. 



THE LUNGS 



Where the lower end of 

 the trachea enters the tho- 

 rax, it divides into right and 

 left bronchial tubes which 

 immediately enter the lungs. 

 Each lung is an elongated, 

 elastic bag of spongy tissue 

 and completely fills one half 



Bronchioles- ' 



Luny 



FIG. 98. THE TRACHEA AND LUNGS 



Showing the air passages. The position of of tne thoracic Cavity, if 

 the thyroid glands is shown in dotted we leave OUt of aCCOUnt the 

 lines. (Modified from Sappey) . , , 



part occupied by the heart 



and large blood vessels. The shapes of the lungs cannot be 

 easily described, since each fits closely about the bordering 

 structures, the heart, the walls of the cavity and the dia- 

 phragm below. The right lung is a little larger, though shorter, 

 than the left; Fig. 73. The lungs are divided into lobes, alike 

 in construction; the right lung has three and the left two 

 lobes, each lung thus being a compound structure. 



