OCR Text |
Show 16 MR. F. E. BEDBARD ON THE [Jan. 17, These muscles are limited to the membrane of the stomach and cesophagus, and do not extend behind the extremity of the lungs. The bands of muscle vary in size. In Chlamydosaurus there are some differences in detail from the conditions characteristic of Physignathus. The mesogastrium is much more distinctly double than the mesogastrium in Physignathus, owing to the greater size of the stomach, which lies across the dorsal middle liver, instead of to the left only. With this is associated not only the much more distinctly double character of the mesogastrium, but its much greater muscularity. The membranous intervals between the muscular strands are so much reduced, that each mesogastrium looks like a thin muscle of coarse texture. I have already mentioned that the umbilical ligament is not muscular. If there are muscles in the pulmo-hepatic, pulmo-parietal, and gastro-hepatic ligaments, they must be microscopic. The mesentery proper has only muscular fibres at its very beginning, and these run at least chiefly to the stomach. Amphibolurus is somewhat intermediate between Physignathus and Chlamydosaurus. There is some development of muscle in the umbilical ligament posteriorly, which for the most part passes out upon the gastro-hepatic ligament and ends in contact with the walls of the stomach, and not, so far as I can make out, upon the liver. The posterior end of the pulmo-hepatic ligament is similarly invaded by muscular strands. The mesogastrium is very distinctly muscular, but not so markedly as in Chlamydosaurus, though perhaps rather more so than in Physigiuiihus. That the Iguanidae and the Agamidse are very closely allied families is admitted. It is not therefore without importance to compare the conditions which obtain in Iguana in respect of the invasion of the mesenteries by muscular tissue. I have examined from this point of view two specimens of Iguana tuberculata, and find the following state of af f ai rsThe umbilical ligament is absolutely single and does not divide into two sheets posteriorly; it lies entirely to the left of the gall-bladder and contains no muscular fibres. The mesogastrium is invaded by a moderate amount of muscular tissue, but none of the other mesenteries that have been referred to in the foregoing account of various types of Agamidse shows any such thick strands of invading muscular tissue in Iguana as they do in some of the Agamida\ It seems likely therefore that this character will be of some use in framing descriptions of the several families of Lizards. Some Arteries in Urornastix*.-The epigastric arteries originate in Urornastix, as in Iguana, from the subclavians. In the former genus, the artery pursues a rather complicated course before passing down the inside of the abdominal wall as the epigastric artery. The main branch of the subclavian traverses the sternal region and appears on the ventral surface of the sternum, * See Calori, Mem. Ac, liologua, 1862, p. 525, for other details of vascular system. |