1891.] ORGAN IN THE CROCODILIA.' 157 



Lizard in a backwardly displaced position, such as it might have 

 come to assume under changes incident ou 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, the conclusion seems, 

 to me, inevitable that those animals from vphich both Crocodilia 

 and Mammals have descended must have possessed, among other 

 things, a vomer vphich met the pterygoids behind, and, like that of 

 the Tchthyopsida and lovper Amniota, extended to the premaxillary 

 region in front, — in a word, the vomer of the living Hatteria. Born 

 has shown Hhat the Jacobcou'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 buUate palatine lobe 

 of Caiman niger would result. Klein has shown ^ that whereas in 

 the Rabbit the cartilaginous sheath of Jacobsou'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. Tn this, the palatine process of the premaxilla of the 

 mammal, assuming its apparent vomerine homology, clearly approx- 

 imates 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 orgau becomes very great indeed ; especially if, 

 as is sometimes stated, that organ may ^ " 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 CrocodiHan premaxilla {p.m., fig. 1) often bears that 

 which might at first sight be taken to represent a palatine process 

 (j).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 Crocodiius 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. Ed. V. 



' Loc. cit. pp. 554-555. 



^ Wiedersheim, Lehrb. d. vergl. Auat., Aufl. 2, p. 400 (1886). 



