236 



ANATOMY AND PHYSIOLOGY 



extending one inch above the clavicle, the base resting upon the 

 diaphragm. The right lung is broader and shorter than the other, 



but it has three lobes, upper, middle, and 

 lower. The left lung has two lobes. 



Note. The left lung is narrower 

 than the right and does not cover the 

 apex of the heart, otherwise it would be 

 exposed to the motion of the "heart 

 beat." 



The lung substance consists of 

 branches of the bronchi and their divi- 

 sions down to the bronchioles, and the 

 spaces terminating in air-cells. These 

 structures are surrounded by blood- 

 vessels, nerves, and lymphatics, grouped 

 together in lobules, supported by fine 



FIG. 159. CLUSTERS OF 

 AIR-CELLS. (Hoi den, from 

 Kolliker.) 



fibre-elastic tissue and wrapped in pleura. 



Each bronchiole terminates in a lobule. 



The root of the lung 

 is composed of the large 

 bronchial tubes, blood- 

 vessels, and nerves (Fig. 

 160). 



The bronchial tubes are 

 the primary divisions of the 

 bronchi; the blood-vessels 

 are first, the bronchial ar- 

 teries for the nutrition of the 

 lung substance; second, the 

 pulmonary arteries which 

 form a fine network of capil- 

 laries around the air-cells, 

 third, the bronchial and pul- 

 monary veins. They enter 

 and leave the lung at the 

 hilum a depression on the 

 medial surface. 



FIG. 1 60. THE LUNGS WITH HEART 

 BETWEEN THEM. 



THE PLEURAE 



Each lung is covered (except at the root) by a thin transparent 

 sac of serous membrane called the pleura. One side of this sac is 



