248 



THE RESPIRATORY SYSTEM 



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 bron- 

 chioles are usually accompanied by the artery only. Those veins 



which accompany 

 the bronchi receive 

 smaller branches 

 from the bronchial 

 wall and by union 

 with their fellows 

 form larger and 

 larger vessels which 

 finally make their 

 exit as the pulmon- 

 ary veins and pass 

 to the left auricle of 

 the heart. 



The bronchial ar- 

 teries also follow the 

 bronchial tubes in 

 all their ramifica- 

 tions. The larger 



FIG. 211. FROM THE CENTRAL PORTION OF THE branches are found 



a, two pulmonary alveoli in transection ; i, tangential f .ji , 



section showing the bottom of an alveolus; c, a minute 

 pulmonary venule. Photo, x 500. lages, the smaller 



ones lie in the sub- 

 mucous and mucous coats. In contradistinction to the pulmonary 

 vessels the bronchial arteries are found in the wall of the bronchi, 

 not outside of the bronchial wall. They supply capillaries to all 

 of the tissues 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 in- 

 terlobular 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 bronchial vein which, lying in the 

 fibrous tissue of the bronchial walls, retrace the course of the 

 bronchi to the hilum, where they make their exit as the bronchial 



