264 MANUAL OF HISTOLOGY. 



veins and capillary plexuses and overflow into the pulmonary 

 arteries. 1 



It appears from this that part of the blood from the bron- 

 chial arteries does, or may, return through the pulmonary veins. 

 In their course through the lung, the pulmonary arteries lie 

 upon the upper and anterior aspect of the bronchial tubes, 

 while the veins are found on their inferior surface. The bron- 

 chial arteries follow the tubes and divide with them. 



The lymphatics of the alveolar septa are a series of lacunar 

 spaces lined by branched connective- tissue corpuscles, whose 

 nuclei have already been described as being visible in ordinary 

 sections of the lung. 



In sections of a lung treated with silver nitrate the forms 

 of the cells are distinguishable. According to Klein the pro- 

 cesses of these cells pass upward between the epithelial plates 

 of the alveoli so as to bring the cells into direct communica- 

 tion with the cavity, just as we have seen the interepithelial 

 cells of the bronchial mucous membrane send certain processes 

 upward between the columnar epithelia and others downward 

 to the cells of the lymph lacunae. On examining the epithelium 

 of an alveolus, small, round, dark spaces are seen between the 

 cells ; these are said by Klein to be the projecting processes of 

 the branched cells of the lymph lacunar system. The ends of 

 these processes, both here and on the bronchial mucous mem- 

 brane, are called pseudostomata, in contradistinction to the 

 true stomata of the serous membranes. 



The small spaces, or lacunae, open into lymphatic radicles, 

 which have a regular endothelial lining. These pass inward 

 toward the root of the lung, upon the bronchi and the walls 

 of the vessels. On the vascular walls they communicate freely 

 with each other, and at times completely invest the vessel with 

 a lymphatic sheath like that of the cerebral vessels. In this 

 situation they are called perivascular lymphatics. The peri- 

 vascular and peribronchial lymphatics communicate freely. At 

 the surface of the lung there is a plexus immediately beneath 

 the pleura (subpleural lymphatics) from which trunks of some 

 size run to the root of the lung. They communicate with the 

 perivascular system and with the pleural cavity. The final 

 termination of all these channels is in the bronchial glands. 



1 Dr. Waters. 



