OCR Text |
Show 1867.] DR. J. MURIE ON PHASCOLOMYS PLATYRHINUS. 809 truncation of the body or shield-like flattening so very remarkable in the living Platyrhine Wombat. P. latifrons differs from the other species in having the transverse processes of the sacral vertebrae shortening from the first to the fourth; in other words, the sacrum narrows behind, whereas in P. platyrhinus and P. wombat it is as broad, if not broader posteriorly than anteriorly. Caudal Vertebrce.-In all the species the first six have transverse processes, the seventh vertebra in each presenting a rudimental one. The processes generally of the remaining caudal vertebrae are very obscure, and the last two or three are little better than tiny ossicles. In P. platyrhinus the great length and breadth of the backwardly inflected transverse processes of the first three or four caudal vertebrae is somewhat remarkable. These almost reach the tuber ischii, so that the sacral and these anterior caudal vertebrae taken together present a long, broad, and flat shield, which in the live animal (P. niger of Gould) in the Gardens is very conspicuous. The Common Wombat, though very much resembling P. platyrhinus in its caudal elements, seems to have the transverse processes relatively shorter, and consequently to present a greater interspace between their tips and the inner border of the ischium. P. latifrons is readily distinguished by the very much shorter and pointed nature of the caudal transverse processes; but these are, moreover, comparatively broader antero-posteriorly at their roots than in P. wombat and P. platyrhinus. From this shortening of the outstanding transverse processes, and a more or less greater length in the vertebrae themselves, the caudal region in P. latifrons entirely wants the short truncated aspect present in the other two species. In all the animals when alive the tail is very short, but it is more perceptible in the Hairy-nosed Wombat than in Common and Platyrhine species. Sternum and Bibs. Sternum.-I have found the bones of the sternum of the specimens of the Platyrhine and Hairy-nosed species, except in one instance, four in number, as is the case in the Common Wombat. In the exceptional example (a portion of a disarticulated skeleton of P. platyrhinus in the College of Surgeons, at present labelled P. wombat) there are five bony pieces composing the sternum. This peculiarity in the number of sternal elements is a reversion to what obtains in the Petaurus taguanoides. The sternal bones oi P.platyrhinus are altogether much the largest of the three, but those of P. latifrons are relatively the stoutest. The hindermost bone, that to which the xiphoid cartilage is attached, is broadened posteriorly in P. platyrhinus, the fifth rib-cartilages abutting against the lateral protruding portions. In P. latifrons this bone is obtusely pointed, and in P. wombat more abruptly truncated posteriorly. Ribs.-The Common Wombat has been regarded as very anoma- P R O C . Z O O L . Soc-1867, No. LII. |