THE LUNGS. 



581 



regularly, with each other, or with branches of other lobular arteries, 

 and, finally, terminate in the capillary plexus of the air-cells. This 

 plexus, which is one of the 

 closest existing in 

 estimated in moist 



Fig. 239. 



Man, as 

 prepara- 

 tions, presents rounded or 

 oval meshes 0-002-0-008 of 

 a line wide, and vessels of 

 0-003-0-005 of a line in 

 diameter. It lies in the wall 

 of the air-cells, at a distance 

 of about 0-001 of a line from 

 the epithelium, in the middle 

 of the fibrous tissue, and is 

 continuous, not only over all 

 the alveola? of one of the 

 smallest lobules, but, also, at 

 all events, in the adult, is 



partially in connection with the plexuses of the contiguous lobules. 

 The pulmonary veins arise from the above-described capillary plexus, 

 with roots which lie more superficial than the arteries, and more exter- 

 nally on the smallest lobules, then run deeply between them, and unite 

 with other lobular veins into larger trunks, which proceed in part with 

 the arteries and bronchial tubes, in part more isolated by themselves, 

 through the pulmonary parenchyma. 



The bronchial arteries are distributed, firstly, to the greater bronchia, 

 whose vessels present the same conditions as those of the trachea, then 

 to the pulmonary veins and arterie?, the latter of which, in particular, 

 possess an extremely rich, vascular plexus, which may be traced as far 

 as branches of -J- of a line, and less; lastly, to the pleura pulmonalis, the 

 branches destined for which are, some of them, given off even at the 

 hilus and in the fissures between the main lobes, some also from the 

 vessels accompanying the bronchia*, coming out between the secondary 

 lobules. Small vessels, moreover, which are not derived from the 

 bronchial arteries, pass on the pulmonary ligaments to the pleura. 



The lymphatics of the lungs are very numerous. The superficial 

 lymphatic vessels run in the subserous connective tissue and in the inter- 

 spaces between the larger and smaller lobules, forming a superficial, 

 finer, and a deep, coarser, angular network, which covers the entire sur- 

 face of the lungs, and on the one hand empties itself into special, super- 

 ficial trunks accompanying the bloodvessels of the pleura towards the 

 root of the lung, and, on the other, opens into the deeper vessels by 

 numerous trunks which penetrate between the lobules. These arise 



FIG. 239. Capillary plexus of the human air-cell, magnified GO diameters. 



