MR. W. K. PARKER ON THE OSTEOLOGY OF BALiENICEPS REX. 305 



and their meaning not at first sight evident ; we have been only lately enlightened upon 

 this subject by Professor Huxley himself, who has kindly demonstrated their structure 

 to us in the Gavial. 



In these reptiles (the Crocodilia), both the external, or anterior, and the posterior 

 nares have a mammalian character ; for the latter openings are not simply bounded 

 externally and posteriorly by the palatines, as in birds, but those openings which agree 

 with the posterior nares of the Bird are entirely shut from view in the palatine aspect 

 of the skull. This is caused by the development of a very perfect palatine inferior 

 plate to these elongated bones, the long palatine groove beneath the basis cranii being 

 thus converted into a canal which is more or less divided into two parallel passages 

 by the vomerine slips of bone, whilst the passages or tubes open on the posterior half 

 of each pterygoid on its inner margin, where it joins its fellow of the opposite side 

 and sends forwards a sharp process to join the vomer, just as the palatine does in the 

 Bird. 



The palatines of the Fowl are ossified before the eleventh day of incubation. The vomer 

 of the Fowl is ossified by the end of the fourteenth day of incubation in the blastema that 

 connects the rudimentary upper maxillary apparatus of each side ; not apparently in 

 pre-existent cartilage, but evidently in the membrane coating the ethmo-vomerine car- 

 tilage behind, and the sphenoidal rostrum in front. In the air-breathing Ovipara gene- 

 rally, the vomer seems to belong to the palato-maxillary apparatus quite as much as to 

 the cranio-facial axis, and to be a sort of morphological bond between the skull and 

 facial arches. In the Fish, however, it is an inferior ossification of the ethmo-vomerine 

 cartilage, and bears upon it the ethmoid in the mid-line and the pre-frontals on each 

 side. The relation of the vomer to the lateral masses of the ethmoid is exceedingly 

 important, these masses being evidently the mammalian condition of the pre-frontals ; 

 Dr. Cleland has shown this with great clearness in his valuable paper ; and one cannot 

 help comparing the thin cortical mammalian vomer, becoming on each side one with the 

 ethmoidal masses, to the thin basi-temporals of the Bird, which are so intimately con- 

 nected with the structures of the ear, and which bear a similar relation to tlie basi-sphe- 

 noid that the vomer of the Mammal does to the central plate of the ethmoid. 



Professor Owen (quoted by Professor Goodsir, op. cit. p. 146) describes (in the Osteo- 

 logical Catalogue, p. 166, No. 764) the skull of the Black Alligator {A. niger), in which 

 " the vomer is divided at the median line, and the anterior expanded part of each moiety 

 appears upon the bony palate, between the pre-maxillary and the maxillary ; the palatine 

 suture between the same bones bending down to the hinder border of the palatal anterior 

 aperture of the nostrils." 



Now, there are conditions of the vomer in other vertebrates curiously illustrative of 

 this exceptional structure in the Crocodilian. Perhaps the Chelonian that comes nearest 

 to the Crocodile in structure is the Logger-head Turtle {Caretta caouana) ; in this 

 creature the maxillary palatal plates meet and articulate, but are separated posteriorly 



