THE SKELETON IN REPTILES. THE SKULL. 283 



formed by a post-temporal bar, formed by the parietal and 

 squamosal. Below the supra temporal arcade is another large 

 vacuity, the infra-temporal or lateral temporal fossa (fig. 

 52, 21). This is bounded above by the supratemporal arcade, 

 and is separated from the orbit in front by the postorbital 

 bar, formed by the union of outgrowths from the jugals and 

 postorbitals. Behind it is bounded by a continuation of the 

 post-temporal bar formed of the squamosal and quadratojugal, 

 and below by an infratemporal arcade, which is chiefly com- 

 posed of the quadratojugal and jugal. 



Below the post -temporal bar is a third vacuity, the 

 post-temporal fossa (fig. 52, D, 23), bounded above by 

 the post-temporal bar and below by the exoccipital and 

 opisthotic. 



Sphenodon and the Crocodilia are the only living reptiles 

 with complete supratemporal and infratemporal arcades, but 

 they are both present in the extinct Pterosauria and some 

 Dinosauria. 



Supratemporal fossae, bounded below by supratemporal 

 arcades, occur in all reptiles except some Chelonia, the Ophidia, 

 the Geckonidae among Lacertilia, and the Pariasauria and 

 others among Theromorpha; they are specially large in No- 

 thosaurus among the Sauropterygia, Dicynodon among the 

 Theromorpha, and many Crocodilia and Pterosauria. In some 

 Dinosaurs, such as Ceratosaurus, they are very small, while 

 the infratemporal fossae are correspondingly large. 



In Elginia 1 (Theromorpha) and some Chelonia, such as 

 Chelone, there are no fossae on the surface of the skull, 

 a complete false roof being developed ; in other Chelonia, 

 such as Trionyx, the true cranium is freely visible, the only 

 part of the false roof developed being the infratemporal 

 arcade. 



In many reptiles large pre-orbital vacuities occur ; they 



1 E. T. Newton, Phil. Trans, vol. CLXXXIV, B, p. 431 (1893). 



