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Show 1 9 0 6 . ] VASCULAR SYSTEM OF VARANUS. 611 other species again, I am able to add something to the recorded knowledge of the venous trunks of this-as I consider it-aberrant genus of Lacertilia. Hepatic Portal System.-The Lacertilia generally differ from the Chelonia and the Crocodilia in possessing but one anterior abdominal vein, while the latter, with the exception of Dermo-chelys, possess two*. _ J-lie Ophidia and Hatteria agree with the Lacertilia with some slight exception. Thus in certain Boidse t the anterior abdominal divides after the union of the two pelvic roots to reunite again before entering the liver. It is therefore noteworthy that Varanus niloticus (only this species among those which I have examined ad hoc) has, like these Ophidians, an anterior abdominal which is double for a part of its length. In one specimen the arrangement was as follows:-the right root of the anterior abdominal vein before joining the left root gives off two branches; the first of these is the right anterior abdominal, the second is a vein which brings blood from the ventral surface of the pelvis. The right anterior abdominal is of less calibre than the left or main anterior abdominal trunk; the two unite not far behind the junction of the portal vein with the conjoined anterior abdominal vessels. In a second specimen of the same species the anterior abdominal was also double ; but I am unable to give exact details. So also with a third individual which was dissected by me a good many years ago, but of whose anatomy I possess notes. It will be noted from the above description, that the double character of the anterior abdominal vein in Varanus niloticus may be rather different from that of the Python and nearer to that of the Crocodilia. For in the serpent the double vein occurs after the fusion of the two pelvic roots, while in Varanus the second, smaller, anterior abdominal vein is a direct offshoot of the corresponding pelvic root. It is, that is to say, separate from the very first. Varanus does not show, so far as I have observed, any signs of a doubling of the anterior abdominal vein at the liver end. If the comparison between Varanus and the Crocodilia be justified so far as concerns these features, it is clear that the posterior junction between the right and left anterior abdominals in Varanus niloticus is to be compared with the junction in Crocodilus cataphractusX between the two anterior abdominals, though the situation of this connecting vessel is not precisely the same in both reptiles. Umbilical Vein.-Besides the two epigastric veins already described, there is a median vein which is connected posteriorly with the anterior abdominal and anteriorly opens into the postcaval vein between the two liver-lobes. Its course was ascertained * Burne: " Notes on the Muscular and Visceral Anatomy of the Leatheiy Turtle," P. Z. S. 1905, vol. i. p. 320. f Beddard : " Notes upon the Anatomy of Certain Snakes of the Family Boidse,' ' P. Z. S. 1904, vol. ii. p. 116. X Infra, p. 620. |
