1030 MR. L. R. CRAWSHAY ON THE ARTERIAL [DeC. 11, 



twig thrown out to this region by the same branch of the 

 siihclavia. 



A. jnohnonalis. — After the separation of the cutanea magna, 

 this artery generally divides into two branches, which further sub- 

 divide and break up into a thick interlacing network over the 

 lung. But whereas in all the species of liana under consideration 

 these vessels traversed veiy conspicuously the outer surface of the 

 lung, in both species of £ufo, while still external to the venous 

 network, they traversed the inner wall in so marked a degree 

 that it was necessary to cut open the lung to follow them at all. 



In Bufo horeas (text-fig. 153, p. 1029) there was a very remark- 

 able abnormality on the right side of the body in relation to the 

 origin of ^he pidmonalis. The cutanea magna took off as usual from 

 the end of the 3rd arch, opposite, roughly, to the carotid gland ; 

 the pulmonalis, however, was carried round in common with the 

 systemic arch to the dorsal region as a single large trunk. Reaching 

 the dorsal body- wall, first was given ofi' the subclavia, secondly the 

 occipito-vertehralis, and lastly the j)ulmonalis, separating from the 

 aorta and descending again round the oesophagus to the lung. A 

 closer investigation by means of a series of transverse sections 

 cut through the arches, showed the true state of things to be that 

 the third arch was concerned throughout with the cutanea magna 

 exclusively, having no connection whatever with the pulmonalis. 

 The latter simply lan in a common trunk with the systemic arch, 

 in which thei-e was no trace of a septum anywhere. 



It is difiicult to form a satisfactory inference as to how such a 

 condition can have arisen in the embryo. The exclusive asso- 

 ciation of the posterior arch, from the outset, with the cutanea 

 magna is wholly inconsistent with the generally accepted view 

 that this artery originates, in common with the JO^^Z7?^o««Z^s, 

 from the fourth branchial arch of the embryo. On the other hand, 

 the entire absence of any septum in the lumen of the systemic 

 arch leaves little ground for supposing that the third branchial 

 arch has persisted as the pulmonalis. It would appear that, 

 under abnormal circumstances, in the embryo a connection had 

 arisen irregularly between the second branchial arch and the lung, 

 and had so persisted, the fourth branchial arch becoming simply 

 the cutanea magna of the adult. 



The normal arrangement of the pulmo-cutaneous arch on the 

 left side of the body is shown in the figure of this Toad (text- 

 fig. 153, p. 1029). 



Appendix. 



[On a direct Vascular Connection between the Mesenteric System 

 and the Lungs in Rana temporaria. (Text-figs. 154, 155.) 



While this paper was in the press, I received from Mr. W. 

 "Woodland a specimen of Rana ten\poraria exhibiting a very re- 

 markable case of a connection between the mesenteric circulatory 

 .system and the lungs. Mr, Woodland, who lately observed 



