g 4 THE VITAL PROCESSES 



artery conveying blood to the lungs is fas pulmonary artery. 

 This starts at the right ventricle and by its branches con- 

 veys blood to the capillaries surrounding the alveoli in all 

 parts of the lungs. The branches of the pulmonary artery 

 lie alongside of, and divide similarly to, the bronchial 

 tubes. At the places where the finest divisions of the air 

 tubes enter the infundibula, the little arteries branch into 



the capillaries that pene- 

 trate the infundibular walls 

 (Figs. 38 and 39). From 

 these capillaries the blood 

 is conveyed by the pulmo- 

 nary veins to the left 

 auricle. 



The lungs also receive blood 



FIG. 40. -The pleura. Diagram from two ( in some individuals 

 showing the general form of the pleural three ) sma11 arteries branching 

 sacs as they surround the lungs and fr m the aorta, known as the 

 line the inner surfaces of the chest bronchial arteries. These con- 

 Other parts removed). A, A'. Places vey to the lungs blood that has 

 occupied by the lungs. B, B' . Slight already been supplied with oxy- 

 space within the pleural sacs contain- gen, passing it into the capilla- 

 ing the pleural secretion, a, a\ Outer ries in the walls of the bronchi, 

 layer of pleura and lining of chest bronchial tubes, and large blood 

 walls and upper surface of diaphragm, vessels, as well as the connect- 

 6, b'. Inner layer of pleura and outer ive tissue between the lobes of 

 lining of lungs. C. Space occupied the lungs> Thig blood leayes 

 by the heart. D. Diaphragm. thg ]ungs parUy by the bron . 



chial veins and partly by the pulmonary veins. No part of the body 

 is so well supplied with blood as the lungs. 



The Pleura. The pleura is a thin, smooth, elastic, and 

 tough membrane which covers the outside of the lungs 

 and lines the inside of the chest walls. The covering of 

 each lung is continuous with the lining of the chest wall 

 on its respective side and forms with it a closed sac by 



