OCR Text |
Show 632 MR. G. A. BOULENGER ON SCHLEGEL'S GAVIAL. [June 16 Cuvier (Ossem. Foss.) describes and figures the second rib in Crocodilus porosus as single-headed and attached to the odontoid bone. Owen (Osteol. Cat. Mus. Coll. Surg.) ascribes to the same rib, in Gavialis gangeticus, a forked head attached to two transverse processes of the odontoid bone. According to Stannius (Zoot. Amph. p. 26), the rib is forked and the two branches are attached on the limit between the odontoid bone and the centrum of the axis. Briihl (Skel. Crocod.) figures, in Caiman palpebrosus, the rib as forked, with capitulum and tuberculum on the odontoid bone near its suture with the axis. In Huxley's 'Anatomv of Ver-tebrated Animals' it is described in Crocodilians generally as attached to the os odontoideum and to the second centrum by distinct capitular and tubercular processes. Baur (Amer. Nat. 1886, p. 228) was the first in attempting to show what, if any, differences exist between the genera with regard to the shape of the second rib and its attachment to the vertebrae. I am not able to confirm his statements regarding Gavialis and Alligator. In the case of the latter, the more forward position assigned by him to the costal capitulum may be due to individual variation; but I cannot help thinking the author is mistaken in attributing a rudimentary diapophysis to the neural arch of Gavialis. In the specimens I have examined two very distinct processes are present on the axis-centrum, and I have satisfied myself on a specimen in spirit that the ligamentous capitulum is attached to the upper of these processes, which is widely separated from the supposed diapophysis figured by Dr. Baur. I have examined the atlas and axis in Gavialis gangeticus, Tomistoma schlegeli, Crocodili niloticus, americanus, and porosus, Osteolcemus tetraspis, Alligator mississippiensis, Caiman sclerops C. latirostris, and find important differences, which are deserving of notice. In Alligator, the first rib is attached to the lower surface of the hypapophysis and in contact with, or narrowly separated from, its fellow at the base ; the second rib, in the adult, is deeply forked and attached by its capitulum to the centrum of the atlas, by its tuberculum to the anterior part of the centrum of the axis, which, however, does not develop any tubercle or transverse process. In a new-born specimen I find both capitulum and tuberculum inserted on the axis, showing the rib to shift forward with age, a further confirmation of the view that this rib, usually attached to the first vertebra, really pertains to the second. In Caiman, the first rib is as in the preceding, but the second, deeply forked, is entirely on the centrum of the atlas, without the latter bearing processes for its attachment. In Crocodilus, the first rib is more on the side of the hypapophysis and widely separated from its fellow; the second is but feebly notched in its proximal portion, and the somewhat ill-defined capitulum and tuberculum join two strong knob-like processes on the centrum of the atlas. In Gavialis, the first rib conforms to the preceding type, but |