OCR Text |
Show 14 MR. F. E. BEDDARD ON THE [Jan. 17, The umbilical ligaments of Amphibolurus are more like those of Physignathus than those of Chlamydosaurus; but the conditions observable are at the same time somewhat intermediate between those in the other two. The umbilical ligament divides, as in Physignathus, before the posterior end of the liver, but rather nearer to the end than in that genus. In Chlamydosaurus the conditions are not really different; it presents us merely with the third term in a series, for the umbilical ligament, as mentioned, arises as one sheet from the liver up to the very point of its bifurcation into two lobes ; it then follows both, leaving the gall-bladder between. In Physignathus a tiny fragment is cut oft" each of the two lobes of the liver, and these lie between the tent-like folds of the posterior region of the umbilical ligament. Finally, in Amphibolurus a large piece of liver-substance belonging to the left lobe as well as a small piece belonging to the right lobe, in addition, of course, to the gallbladder, lie sheltered by the posterior divided region of the umbilical ligament. As in Chlamydosaurus, no muscular layer passes out upon the liver. It is plain, therefore, that in these characters Chlamydosaurus does not stand markedly apart from its allies. The liver, however, is rather more compressed and not quite so broad from side to side as in Physignathus and Amphibolurus, especially in Amphibolurus. In all these genera the long prolongation of the right lobe (the " Hohlvenenfortsatz " of Hochstetter) extends right down to the testis of its side of the body. There is no great length of vena cava left between testis and liver such as exists in some lizards, e. g. Tiliqua. In the Agamidfe, moreover, there is not always so marked a prolongation of the liver-lobe towards the gonad ; for while in a 2 Agama colonorum the liver-lobe was nearly in contact with the ovary, there was in a 2 Urornastix acanthinurus a considerable stretch of vena cava between the two.M esenteries o f Colon.-In Urornastix acanthinurus, which is a vegetable-feeder, the large intestine is particularly long, and the wide colon with thin greenish walls is sharply to be distinguished from the narrow thick-walled rectum. The whole of the colon and the greater part of the rectum lie outside of the shelter of the pelvic bones. In these particulars Urornastix contrasts with Physignathus. Associated with this is a peculiarity in the arrangement of the mesenteries which is so far peculiar to the genus. In addition to the median dorsal mesentery tying down the gut to the parietes, the colon lias a second mesentery which affixes it to the elongated process of the right lobe of the liver and to the vena cava behind the point where the lobe of the liver ends. This membrane forms the mesorectum at the beginning of the rectum, but it is distinct from it, as is shown by the fact that it is not pigmented, while the mesorectum is, and that its muscular fibres are more abundant and larger. |