OCR Text |
Show 394 DR. J. E. GRAY ON STER/NOTHcERUS. [Apr. 1, STERNOTHCERUS. (Figs. 1, 2, 3, 4, & 5, p. 393.) Skull very depressed, triangular, very broad, expanded, and swollen behind, as wide just before the tympanic cavity as from the front edge of the upper lip to the condyle. Crown flat, with the marks of the sutures between head-shields well impressed, tapering on each side from the back edge of the zygoma to a narrow central prominence. Zygoma very strong, broadband much bent out and convex, leaving a very large space on each side for the temporal muscle, and entirely enclosing the circular deep tympanic cavity. Beneath flat, wide, with a very large reflexed edge to each pterygoid bone, and a large hole in front of it, on the outer side of each palatine, on a level with the front of the zygomatic arch. The internal nostrils united, very large, triangular, with a long depression behind them, as broad as their hinder edge, with a slight central longitudinal promint-nce. Tbe alveolar surface broad, becoming broader behind, with a deep circular central pit in front, for the reception of the point of the lower jaw, and a slight lateral ridge, which commences at the back edge of the central part and extends to the middle of the hinder part of the alveolar surface. The outer edge of the upper jaw sharp, bent in, and forming a deep notch on each side of the central part, which is square and prominent. The orbits are oblong, longitudinal, tbe nose being about half the length of the longitudinal diameter of the orbit. The nose-hole large and square. The lower jaw depressed, strong, acute, and bent up in front, rounded beneath in front, and truncated behind at the gonyx, this part being covered by the horny beak as far as the hinder truncated edge. The sides strong, oblique, flattened. The alveolar surface flattened, slightly concave, with a sharp raised outer and inner edge, and with a triangular surface behind the centre, extending as far back as the truncated gonyx, separated, as is also the under part of the jaw, from the alveolar edge by a longitudinal groove for a bloodvessel or nerve, entering just before the condyle. The skull is 2| inches from nose to condyle, 2\ from cheek to This skull differs from that of Pelomedusa, figured by Dr. Wagler in his ' Nat. Syst. Amphib.' t. ii. figs. 36-44, in being much broader and more depressed, and in having more developed zygomatic arches, and in being more swollen out at the sides, especially behind, also in the nose-hole being more erect and slightly hooded over by the nasals. The lower jaw is very similar ; but the front part of the centre of the alveolar surface is much more produced and bent upwards, and the part of the centre behind the alveolar surface is more produced, concave, and truncated, while in Pelomedusa it is much narrower and regularly rounded. It is to be observed that Dr. Wagler does not figure the alveolar surface of this species. The tympanic cavity is oblong in Pelomedusa, and the edge much more sinuated between the tympanic cavity and the end of the upper jaw. |