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Show 156 MR. F. E. BEDDARD ON A TARASTERNUM [June 7, in Tiliqua was an imperfect representation of that occurring in the Chamaeleon and other lizards, where a number of true ribs join ventrally behind the sternum. Thus in Acontias and Typhlo-saurus, of which the former is a. near ally of Tiliqua, there are present these post-sternal ribs meeting in the middle line, and thus simulating abdominal ribs *. In the Channel eon the most ventral layer of the abdominal musculature is so thin that it requires a careful dissection to show that the ventrally meeting ribs do not lie in this layer but in the deeper layer. In Tiliqua, on the other hand, the ventral musculature is thick, and the two Text-fig. 29. Abdominal ribs of Tiliqua scincoides. A points' to one of these ribs. A meshwork of tendons lies between and over them. layers are easily distinguishable. When the ventralmost layer is raised, the abdominal ribs are carried with it, and are seen to end off in it with slightly forwardly-curved lateral ends. But-more important than this-on the deeper layer of the musculature are two or three cartilaginous bars, lying obliquely (see text-fig. 30, j>. 157), which are clearly the ventral portions of true ribs such as in Acontias make complete hoops. The discovery of these entirely sets at rest any doubt as to the fact that the bars of cartilage which lie superficially are really quite comparable to a parasternum. The true ventral moieties of the ribs are not in connection with their vertebral portions, so far as 1 have been able to ascertain. They would thus be very readily lost in macerated skeletons, and might even be overlooked in a dissection. In his ‘ Catalogue of Lizards * Peters, ‘ Reise nach Mossambique,' Amphibia, pis. xii. & xiii. |
