ORGANS OF RESPIRATION. 



249 



intercostal artery and follow the bronchial tubes 



through the lung, to be ultimately distributed in 



three ways: i. They supply the bronchial lymph 



glands, the coats of the large blood-vessels, and the 



walls of the bronchial tubes, forming in the latter 



an outer and an inner plexus for the irrigation of the 



muscle coat and the mucous membrane. 2. They 



supply the interlobular areo- 



lar tissue; and 3, They spread 



out over the surface of the lung 



beneath the pleura. The 



bronchial veins do not have so 



extensive a distribution be 



cause some of the blood sup- 



plied by the bronchial arteries 



returns by the pulmonary 



veins. The superficial and 



deep set of bronchial veins 



unite at the root of the lung 



to drain on the right side into 



the large azygOS and On the 

 t r. . .1 1 f. 



left into the left upper azygos 



Vein 

 ' 

 The pulmonary artery, 



which supplies the venous 

 blood, is a very large vessel 

 that gives branches to each 



lobe of the two lungs. The relation of the pul- 

 monary artery to the bronchi is different on the two 

 sides. On the right side the first branch of the pul- 

 monary artery turns backward below the bronchus 

 of the upper lobe, and then passes along the posterior 



^ _ Reconstruc . 



tion in wax of a single atri- 

 um and air sac with the 



a i veoH: V} surface where 



atrium was cut from alveolar 

 duct; P, cut surface, where 

 another air sac was re- 



(after Miller). 



