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Show 1 0 3 0 MR. L. R. CRAWSIIAY ON THE ARTERIAL [D e c . 1 1 , twig thrown out to this region by the same branch of the subclavia. A. pulmonalis.-After the separation of the cutanea magna, this artery generally divides into two branches, which further subdivide and break up into a thick interlacing network over the lung. But whereas in all the species of Rana under consideration these vessels traversed very conspicuously the outer surface of the lung, in both species of Bufo, 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 boreas (text-fig. 153, p. 1029) there was a very remarkable abnormality on the right side of the body in relation to the origin of the 'pulmonalis. 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. Beaching the dorsal body-wall, first was given off the subclavia, secondly the occipito-vertebralis, and lastly the pulmonalis, 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 ran in a common trunk with the systemic arch, in which there was no trace of a septum anywhere. It is difficult to form a satisfactory inference as to how such a condition can have arisen in the embryo. The exclusive association 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 pulmonalis, 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). A p p e n d ix . [On a direct Vascular Connection between the Mesenteric System and the Lungs in Rana temporaria. (Text-figs. 154, 155.) W hile this paper was in the press, I received from Mr. W. Woodland a specimen of Hctna temporaria exhibiting a very remarkable case of a connection between the mesenteric circulatory system and the lungs. Mr. Woodland, who lately observed |