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Show 150 PROF. G. B. H O A V E S O N JACOBSON'S [Feb. 17, prolongation of the vomer1. The pterygoids of the Crocodilia (pt., fig. 2) unite before reaching the vomers to form a gutter-like bed for reception of the free edge of the septum nasi (cf. fig. 5), in a manner repetitional of that of the Mammalian vomer. They furnish, as is well known, the median longitudinal partition for the narial pharynx (marked pt. in fig. 1), and the rostrum formed by their union bifurcates antero-dorsally to give attachment to the vomers, while antero-ventrally it tapers off into a delicate spur (* of fig. 1) which enters the palatines from behind, and may be traced forwards through their substance to the region of the maxillo-palatine suture (s.mp.). Setting this spur aside, the point of termination anteriorly of the pterygoid rostrum (pt., fig. 1) is usually coincident with that of the post-palatine foramen (f.pl."). In Caiman niger (fig. 1) it lies well in front of this; and, as the vomer in that animal extends forwards to an unusual degree, it might appear that there is, so to speak, a sympathy or correlation of growth between the two bones. Indications of such a correlation are forthcoming on comparison of a series of skulls, but examination of a larger number is needed before more can be said upon this point. Another and perhaps more significant feature arrested my attention, while comparing a series of longitudinal sections of skulls of Crocodilus palustris and Alligator mississippiensis of different ages-viz. that the vomer reaches farthest forwards in the younger individuals, and that, whereas in the adult Crocodilus palustris the point of anterior termination of the pterygoid rostrum (pt., fig. 1) closely approximates, as has been said (supra), to that of the post-palatine foramen (fipl.'), in the young (half-grown) individual it lies well in front of it. In other words, there is evidence to show that during the early post-embryonic life of the Crocodile the vomers and pterygoids grow less rapidly than the adjacent bony parts, and become, as it were, shortened up. II. Having adduced reason to believe that the Crocodilian vomer in all probability undergoes, in ordinary, a process of shortening up during early life, the question naturally presents itself whether the differences between the vomer of Caiman niger and the other short-nosed Crocodilia might not be expressive of degrees of abbreviation of that bone from before backwards; and if so, whether that which I have here termed its palatine lobe (above, p. 149) may not represent something which the remaining Crocodilia have lost. 1 have already shown that, among those forms examined by myself, Alligator mississippiensis approximates most nearly to Caiman niger in the forward prolongation of its vomer ; and, with this fact in mind, I naturally turned to the former animal as most likely to yield traces of the missing parts. In this I was not disappointed, as the sequel will show ; and my investigation has brought to light some facts of unexpected interest. Upon first comparison ot the skulls of Caiman niger and Alligator 1 Cf. Boulengcr, op. cit. pp. 2, 17. |