THE LUNG 



317 



The interlobular veins (pulmonary veins) follow the fibrous septa 

 toward the hilum. They soon come into relation with the bronchi and 

 are then found on that side of the bronchus opposite the pulmonary 

 artery. The vein, like the artery, lies outside of the bronchial wall in 

 the adjacent fibrous tissue. It is, as a rule, only those bronchi whose 

 wall contains cartilage plates which are in relation with both pulmonary 

 artery and vein; the smaller bronchioles are usually accompanied by the 

 artery only. Those veins which accompany the bronchi receive smaller 

 branches from the bron- 

 chial wall and by union 

 with their fellows form 

 larger and larger vessels 

 which finally make their 

 exit as the pulmonary 

 veins and pass to the left 

 auricle of the heart. 



The bronchial 

 arteries also follow the 

 bronchial tubes in all 

 their ramifications. The 

 larger branches are found 

 in the outer fibrous coat 

 near the cartilages, the 

 smaller ones lie in the 

 submucous and mucous 

 coats. In contradistinc- 

 tion to the pulmonary 

 vessels the bronchial ar- 

 teries are found in the 

 wall of the bronchi, not 



outside of the bronchial wall. They supply capillaries to all of the tis- 

 sues of the bronchi. The bronchial capillaries reunite to form small 

 venules whose course differs with the size of the tube. In the terminal 

 bronchioles these venules pass directly to the interlobular veins, and, 

 according to Miller, the pulmonary veins receive a similar acquisition 

 at each division of the bronchi. In the larger bronchi, however, the 

 venules unite within the bronchial wall to form the radicals of the bron- 

 chial vein which, lying in the fibrous tissue of the bronchial walls, re- 

 trace the course of the bronchi to the hilum, where they make their exit 

 as the bronchial veins and join the azygos veins. Thus, only the walls 



FIG. 300. FROM THE CENTRAL PORTION OF THE 

 PRECEDING FIGURE. 



a, two pulmonary alveoli in transection; b, tan- 

 gential section showing the bottom of an alveolus; 

 c, a minute pulmonary venule. Photo. X 500. 



