THE SKULL OF REPTILES 



63 



tainly-known reptile with a single typical upper temporal vacuity. 

 The roof bones are all paired in all, so far as known. In Araeoscelis, 

 Plenrosaurus, and ^rohahXy Protorosaurus . there is a parietal foramen, 

 but none in Saphaeosaurus. The lacrimal is small or vestigial in all. 

 The postfrontal is present in Araeoscelis, and only in this genus are 

 there indications of the presence of the dermosupraoccipitals. Prob- 

 ably all have teeth on the palatal bones. 



Their chief interest lies in the structure of the temporal region. In 

 Araeoscelis the temporal opening is bounded externally by three 



Fig. 52. 



Parapsid skulls: A, Pleurosaurus, from the side. Natural size. 

 B, Araeoscelis, from the side. Twice natural size. 



bones, the postorbital in front, and two bones posteriorly, about 

 which there is doubt because of their evident identity with the cor- 

 responding bones in the lizard skull, which have been the subject of 

 more controversy than any others of the reptilian skull. Aside from 

 the tabular, there are three recognized bones of the primitive tem- 

 poral region, all present in the Cotylosauria and Ichthyosauria, to 

 which the names mastoid, supramastoid, squamosal, suprasqua- 

 mosal, prosquamosal, temporal, supratemporal, and quadratojugal 

 have been applied in almost all possible combinations. Only two of 

 these are present in Araeoscelis, Pleurosaurus and the Squamata, to 



