62 



THE OSTEOLOGY OF THE REPTILES 



Owen to the present. The large temporal vacuity is admittedly the 

 upper one, bounded on the inner side by the parietal, on the outer by 

 the postfrontal and the so-called supratemporal. There is no lateral 

 foramen, and it is quite improbable that a preexistent one was later 

 closed by the encroachment of the orbit. This region, as in the primi- 

 tive skull, has five bones. About three, the postfrontal, postorbital, 

 and quadratojugal, there can be no question of identity. And un- 

 less we accept the wholly improbable theory that new bones have 

 been developed in the temporal region of the ichthyosaurs, the other 

 two must be homologized with the supratemporal, or tabular, and 



the squamosal. The supratem- 

 poral bone was the first to be 

 lost in the primitive skull, and 

 there is no certain evidence yet 

 forthcoming that it was re- 

 tained in any reptiles after the 

 cotylosaurs. If, however, the 

 supratemporal was persistent 

 '"g in the ichthyosaurs instead of 

 the tabular, by no possibility 

 can it be the bone on the outer 

 side of the squamosal, as some 

 recent writers assert, as a com- 

 parison of the cotylosaur skull 

 will make evident. The outer 

 bone, sometimes obsolete in ichthyosaurs, must be the squamosal. 

 The upper, posterior bone completing the upper border of the tem- 

 poral vacuity, the author prefers to believe is the tabular and not 

 the supratemporal, and doubtless is homologous with the bone so 

 recognized in the skull of the Squamata. We cannot conceive of 

 its being anything else, having as it does the same relations with 

 paroccipital, parietal, and quadrate, rarely in the mosasaurs extend- 

 ing forward to articulate with the postorbital. 



The Skull of the Protorosauria 



(Figs. 52, 53 c-e) 



In the order here provisionally called the Protorosauria the skull 

 is completely known in none, but best in Araeoscelis, the oldest cer- 



FiG. 51. Ichthyosaur skull: Baptanodon 

 {Ophthalmosaurus), from the rear. After 

 Gilmore. Ang, angular; bs, basisphenoid; 

 d, dentary;/r, frontal. 



