OCR Text |
Show 620 MR. F. E. BEDDARD ON THE [May 29, on the right side, in common with the internal mammary *, from which it soon diverges and runs the usual course to near the dorsal middle line. It is remarkable that on the left side (only, not on the right) the azygos arises by two origins-a thicker anterior trunk, and a much more slender posterior vessel. This is quite analogous to what has already been described in Crocodilus cataphractus, including the asymmetry, which is still more remarkable. The azygos also gives off, precisely as in Crocodilus cataphr actus, a vein running along the lateral thoracic parietes. Arrived at the side of the vertebral coloumn some little way in front of the origin of the longus colli muscle (also as in Crocodilus cataphr actus), the azygos does not plunge into the thickness of the parietes as in the last-mentioned Crocodile, but runs back quite superficially as in a Mammal. It is thus displayed for the whole of its course to as far back as where the dorsal parieto-hepatic trunks communicate with it. This course corresponded (at any rate in one of the two specimens dissected) to 6 ribs. The chief difference, therefore, which this species shows from Crocodilus cataphractus is in the possession of superficially running azygos veins. In Caiman sclerops the two azygos veins arise symmetrically with regard to each other from their respective jugulars, right and left. In both cases they arise behind and not very near to the subclavians and separately from the jugular, i. e. not in common with any other vein. Each is closely accompanied by the corresponding artery which is a branch of the carotid. I could detect no lateral parietal branch of each vein ; but as the specimen was quite a small one, they may have remained undetected. Each azygos reaches the dorsal line far forwards at the level of the fourth rib in front of that whose vertebra bears the origin of the longus colli muscle. Then the vein disappears and does not run superficially on each side of the body; but some way in front of the liver it reappears and passes in a slightly sinuous course to the end of the liver, where it gives rise in the usual way to the hepatic branches, which will be described later. Thus the present genus agrees to some extent with Osteolcemus in the superficial course of the two azygos or posterior vertebral veins, there being the difference that in Caiman the vein runs superficially only posteriorly. The artery is superficial throughout. Anterior Abdominal Veins.-These veins, which, as is well known, are completely double in the Crocodilia, show certain differences in different species. Rathke has called attention t to the fact that the two veins often differ in calibre. He does not mention certain points to which I shall now refer. In Crocodilus cataphractus, as in Crocodilus acutus, a slender vessel leaves the left anterior abdominal vein some way behind the liver, and running obliquely forwards joins the right anterior * Whether this is also the case with C. cataphractus I am not able to say. According to Rathke they are separate in origin. f Loc. cit. p. 257 footnote. |