ORGANS OF RESPIRATION. 



249 



I 



/ 



intercostal artery arid 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 

 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 



A 



Fig. 192. Reconstruc- 

 tion in wax of a single atri- 

 um and air sac with the 

 alveoli: V, Surface where 

 atrium was cut from alveolar 

 duct; P, cut surface, where 

 another air sac was re- 

 moved; A, atrium; S, air 

 sac with air cells (alveoli) 

 (after Miller). 



