THE LUNGS. 177 



cules of the pulmonary artery are apparent in various situa- 

 tions on the surface of the lungs, ramifying under the pleura. 

 Reisseisen (p. 17) describes these vessels, and figures them very 

 beautifully (Tab. IV, V) ; recently, Adriani has traced them in 

 injected lungs and states that they penetrate into the interior, 

 much convoluted and frequently anastomosing ; they are con- 

 siderably thicker, however, and form wider plexuses than those 

 of the alveoli. The blood from these plexuses is conveyed 

 away, on the one hand, by the superficial roots of the pul- 

 monary veins, and on the other, through anastomoses with 

 the ramifications of the vasa bronchialia in the pleura pulmo- 

 nalis. That the pulmonary artery also supplies the bronchia 

 to some extent, was stated by Arnold (Anat. II., p. 171); and 

 to Adriani we are indebted for more precise information on 

 this interesting subject. According to them, the pulmonary 

 artery and veins chiefly participate in the formation of the 

 capillary plexus on the surface of the bronchia, which is cha- 

 racterised by the elongated form of its meshes, and is consti- 

 tuted by vessels almost as fine as those of the air-cells (in Man, 

 of 0*004 — 0006 ), whilst the bronchial vessels are specially 

 destined for the supply of the muscular and fibrous coats of 

 those canals. It is comprehensible, also, that in this situation 

 the two vascular systems are, to a certain extent, connected; 

 and consequently the older anatomists, such as Haller, Som- 

 mering, and Reisseisen, who speak of a connexion between the 

 two vascular systems of the lungs, were quite right. According 

 to Adriani and Rossignol, the bronchial arteries and veins may 

 be injected from the pulmonary veins, and inversely, the pul- 

 monary veins from the bronchial arteries; but the bronchial 

 vessels cannot be filled from the pulmonary arteries. 



In accordance with these facts, a participation in the inter- 

 change of gases may be ascribed also to the finest bronchia, but, 

 on account of the already somewhat increased thickness of the 

 epithelium in them, and the rather wider capillary plexus, to a less 

 extent than in the air-cells. Here also we might recall to mind 

 the dilatation of the bronchial arteries and extension of their 

 zone of distribution, in cases where the circulation through the 

 pulmonary arteries is interrupted [vide Virchow, in his 'Archiv/ 

 III, 3, p. 456), in which cases the bronchial arteries frequently 

 wholly replace branches of the pulmonary artery, and become 



ii. 12 



