3 88 



VESSELS OF THE LUNGS. 



[sect. 178. 



Fig. 161. 



pulmonary lobules, a branch is given off for the supply of each ; 

 this divides into still finer twigs, which usually correspond in 

 number to the smallest lobules, and thus at last the separate air- 

 cells are supplied. The course of these finest ' lobular ' arteries, 

 as they are called, can be very readily traced in a preparation 

 which has been injected, inflated, and dried. Where these vessels 

 extend into the tissue uniting the lobules (infundibula) , they are 

 seen to supply not one lobule only, but always two or three lobules 

 with fine twigs. These penetrate inwards, upon and between the 

 air-vesicles, divide several times during their course among the 



thick elastic trabecular, and occasionally 

 also join each other, or unite with twigs of 

 adjacent vessels, though not in any regular 

 manner. Lastly, the lobular arteries break 

 up into the capillary network of the pul- 

 monary vesicles. In a moist preparation 

 the meshes are seen to be roundish or 

 oblong, and only crooi'" to o # oo8"' in 

 width, while the vessels are 0"003'" to 

 o , oo5" / in diameter; and the plexus is, 

 therefore, one of the closest which occur 

 in the human body. The network of ca- 

 pillaries runs through the fibrous tissue in 

 the walls of the air-cells, and is removed 

 about cool'" from the epithelium; it ex- 

 tends continuously over all the alveoli of 

 an idtimate lobule, and is partially con- 

 nected, also, at least in the adult, with the plexus on neighbouring 

 lobules. The -pulmonary veins arise from the above-mentioned 

 capillary network by means of roots, which lie external to the 

 arteries upon the smallest lobules; they run between the latter, 

 and join with other lobular veins to form larger trunks, which 

 extend through the pulmonary parenchyma, partly with the ar- 

 teries and bronchia, and partly isolated from them. 



The bronchial arteries are distributed, firstly, to the larger 

 bronchial tubes, whose vessels present the same conditions as in 

 the trachea ; secondly, upon the pulmonary veins and arteries, the 

 latter of which more especially possess an extremely rich vascular 

 network, which can be traced upon branches of ■£"' and less iu 

 diameter ; lastly, to the pulmonary pleura, the twigs for which go 

 off, partly at the hilus and in the fissures between the main lobes, 

 partly arise between the secondary lobules from the vessels accom- 



Capillary network of the 

 pulmonary vesicles of man. 

 Magnified GO times. 



