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Show 1906.] VASCULAR SYSTEM OP TIJE 1IELODERM. 603 ascertain, with any veins in the posterior region of the abdomen. It runs, of course, upon the ventral side of the abdominal cavity lying to the left of the anterior abdominal vein. This position at first led me to think that the vein in question was a left anterior abdominal vein, such as is met with in addition to a right in the Crocodilia invariably and in the Chelonia generally. I think, however, that the facts which I have to state about this vein disprove the idea that it is a second anterior abdominal vein and prove it to be a persistent umbilical. This vein is by no means a ligamentous rudiment such as Hochstetter has described and figured * the umbilical to be in Anguis fragilis. It contains plenty of blood ; but it looks rather like an artery owing to its pink colour-due, I imagine, to thickish walls. It is, however, not an artery; for anteriorly it could be followed between the lobes of the liver ventrally, and perhaps about halfway along the length of the liver was traced into communication with the vena cava posterior, which latter, on separating the lobes of the liver, can be seen lying between them. It could be distinctly observed at the same time that various branches of the epigastric vein (see p. 609) which enter the liver near the entry of the umbilical did not communicate with the vena cava but entered the liver-substance. There can be no confusion therefore of this presumed persistent umbilical vein with a branch of the epigastic system of veins. It is further to be noted that the umbilical vein is in its relations to adjoining viscera more like that of birds than of the Boidae, where alone among existing Sauropsida-so far as we know at present-this vein persists in the adult. That is to say, the vein is lost to sight until the two lobes are separated at about the middle of the liver as in the Class Aves, instead of extending beyond the liver as in the Python t for example, and joining the vena cava in front of that organ. On another page* I call attention to the possible persistence of the umbilical vein in the Monitor lizards, which vein, however, shows certain differences from that which I describe in Heloderma as an umbilical. There is no doubt, however, that the vein in Heloderma corresponds to what is clearly the persistent umbilical in the Anaconda, &c. in bearing no part in the cn-culation, i. e. in not being furnished with branches. Anterior Abdominal Vein.-This vein is, as is universal among the Lacertilia §, a single median vein, and was very full of blood in the specimen wdiich I dissected. The origin of the vein in the pelvic region seems to me to be more like that of Varanus than of such other Lizards as have been examined. Of Varanus arenarius ( = V. griseus) Hochstetter || has written :-" Ein zweiter wichtiger Differenzpunkt betrifft die Lage der Wurzel der Abdominalvene, * Morph. .Tahrb. xix. f Beddard, " Contributions to the Anatomy of the Ophidia," P. Z. S. 1906, vol. i. p. ‘28. X Below, p. 611. § Excepting possibly Varanvs (see below, p. 611). j| Morph. Jahrb. xix. p. 467. |