150 PROF. G. B. HOwi;s ON jacobson's [Feb. 1", 



prolongation of the vomer ^ The pterygoids of the Crocodilia {pt., 

 fig. 2) unite befoie reaching the vomers to form a gutter-hke bed for 

 reception of the free edge of tiie septum nasi {cf. fig. 5), in a manner 

 repetitional of that of the Mammalian vomer. Tiiey furnish, as is 

 well known, the median longitudinal partition for the narial pharynx 

 (marked j3#. in fig. 1), anil the rostrum formed by their union bifur- 

 cates autero-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.). 

 Settiug 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 niyer (fig. 1 ) it lies 

 well in front of this ; and, as the vomer in that animal extends for- 

 wards to an unusual degree, it might appear that there is, so to speak, 

 a sympathy or correlation of growth between the two bones. Indica- 

 tions 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 pahisti-is and Alligator mississippiensis 

 of different ages — viz. that the vomer reaches fartiiest forwards in 

 the younger individuals, and tliat, whereas in the adult Crocodilus 

 pahistris the point of anterior termination of the pterygoid rostrum 

 (pt., fig. 1) closely approximates, as has been said (supixt), to that 

 of the j)0=t-palatine foramen if pi.'), 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 o( 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 degrtes of abbre- 

 viation of that bone from before backwards; audit so, whether that 

 which 1 have here termed its palatine lobe (above, p. 149) may not 

 represent something which the remaining Crocodilia have lost. I 

 have already shown that, among those forms examined by myself, 

 Alliyator mississippiensis approximates most nearly to Caiman niger 

 in tlie 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 

 gome facts of unexpected interest. 



Upon first comparison of the skulls of Caiman niger and Alligator 



* Cf. Bouleuger, op. cit. pp. 2, 17. 



