OCR Text |
Show 1891.] ORGAN IN THE CROCODILIA.' 157 Lizard in a backwardly displaced position, such as it might have come to assume under changes incident on the elongation of the snout, or to that of communication between the body of this organ and its duct-the latter having presumably disappeared. From the foregoing facts and considerations, tbe conclusion seems, to me, inevitable that those animals from which both Crocodilia and Mammals have descended must have possessed, among other things, a vomer which met the pterygoids behind, and, like that of the lchthyopsida and lower Amniota, extended to the premaxillary region in front,-in a word, the vomer of the living Hatteria. Born has shown1 that the Jacobson's organ of the Lacertilia is largely supported upon the vomer ; did that bone completely enclose it, a condition of the parts essentially like that of the bullate palatine lobe of Caiman niger would result. Klein has shown 2 that whereas in the Rabbit the cartilaginous sheath of Jacobson's organ (jc, fig. 3) is a complete tube and its bony sheath an incomplete one, in the Guinea-pig the latter tends to form " an almost complete capsule " anteriorly. In this, the palatine process of the premaxilla of the mammal, assuming its apparent vomerine homology, clearly approximates towards the condition of the palatine lobe of the vomer of Caiman niger. Putting the foregoing facts and considerations together, the probability that the vomer of Caiman niger may lodge a (perhaps modified) Jacobson's organ becomes very great indeed; especially if, as is sometimes stated, that organ may 3 " degenerate into a mere air-sinus." I am fully alive to the possibility that, on the grounds laid down by Parker, the vomer of Caiman niger may be perhaps a compound structure. I should be exceedingly grateful to anyone who would procure me well-preserved heads of this animal, old and young, for the further elucidation of the questions raised. If the characters and relationships of the vomer are to be taken as criteria of affinity, I need hardly point out that the facts herein dealt with indicate that the short-snouted Alligators, as represented by Caiman niger, must be considered to be the least modified of living Emydosauria,-the prevailing view to the contrary notwithstanding. V. The Crocodilian premaxilla (p.m., fig. 1) often bears that which might at first sight be taken to represent a palatine process (p.p.); and the existence of this spur of bone appears to have been generally overlooked. It is very variable in its individual deve-lopement, and my own skulls of Crocodilus palustris show that it increases in length with advancing age. It is absent in Caiman niger ; and, when present in other forms, it invariably overlies the maxilla as represented in fig. 1. These facts, in conjunction with 1 Op. cit. Bd. v. 8 Loc. cit. pp. 554-555. 3 Wiedersheim, Lehrb. d. vergl. Anat., Aufl. 2, p. 400 (1886). |