1874.] the Lymphatic System of the Lungs. 135 



I call this system of lymphatics the intermuscular or pleural lymphatics. 

 In the distended lung of the guineapig, these pleural lymphatic sinuses 

 are seen to be covered by hardly any thing but the endothelium of the 

 pleural cavity, between which and the cavities of those sinuses a free 

 communication exists by means of true stomata; so that the endothelium 

 lining the sinuses is here directly continuous with that of the pleural sur- 

 face. In every case of chronic pleuritis induced by injecting irritating 

 substances (such as products of acute and chronic pysemic processes, pro- 

 ducts of indurated lymphatic glands), an active germination of the endothe- 

 lium around those stomata takes place. This germination extends not 

 only to the endothelium of the neighbouring parts of the pleural surface, 

 but also to the endothelium of the intermuscular lymphatic sinuses. The 

 relation between the cells of the membrana propria of the pleura pulmo- 

 num and the endothelium of the surface is similar to that already described 

 by me in other serous membranes, the cells of the propria throwing out 

 processes, which project between the endothelial elements of the free sur- 

 face, thus forming pseudostomata. The pleural lymphatics stand in 

 communication with lymphatic tubes, which lie in grooves, the arrange- 

 ment of which corresponds with that of the most superficial groups of 

 alveoli of the lung. These may be called the subpleural lymphatics; they are 

 provided with valves, and form a network of anastomosing lymphatic ves- 

 sels. The larger trunks run along the ligamenta pulmonum towards the 

 root of the lung. This system of lymphatic vessels is best developed in 

 the lung of the dog, in which it has been described by Wy wodzoff ; it is 

 also well developed in the lungs of rabbits and cats. It receives lympha- 

 tic branches, which take their origin between the alveoli of the superficial 

 portions of the lung. The mode of origin of these interalveolar lymphatics 

 is that already described in my published work. The septa of the 

 alveoli contain branched connective-tissue corpuscles ; the spaces in which 

 these cells lie, forming the lymphcanalicular system, open into the cavities 

 of the interalveolar lymphatics, with the endothelium of which the cells 

 of the lymphcanalicular system are in direct continuity. 



2. Perivascular lymphatics. Besides the system of subpleural lympha- 

 tics, the lung contains two other systems ; of which one takes its origin 

 in the alveolar septa from branched cells exactly like those previously 

 referred to. The lymphatic capillaries of this system lead into vessels 

 that accompany the branches of the pulmonary artery and vein ; they run 

 either in the adventitia of these vessels in twos or threes, anastomosing 

 with each other, or the blood-vessel is entirely, or only half, invaginated in 

 a lymphatic vessel. The branched cells of the alveolar septa, from which 

 the capillaries of this system of lymphatics (which we will call the 

 perivascular lymphatics) originate, have an important relation to the epithe- 

 lium of the alveoli ; lor they send a process, or a greater or less portion 

 of their body, between the epithelial cells into the cavities of the alveoli. 

 These represent pseudostomata, as described by myself for the serous 



