MR. W. K. PARKER ON THE OSTEOLOGY OF BALANICEPS 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 te 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 the 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 
