SKULL REPTILES 



137 



tasnia and a lower middle parietal taenia) in place of the sphenolateral, 

 and having large fenestras between them. Between the orbits these 

 taeniae meet in the interorbital septum, diverging dorsal to the eyes 

 as the supraseptal plates. The nasal capsules are complicated 

 internally. Usually there is an epipterygoid process, but this never 

 fuses with the cranium. The visceral arches are reduced, the 

 posterior being small or absent. 



The skull of the most primitive reptiles (Cotylosaurs, figure 152) 

 is like that of Stegocephals in the numerous bones of the roof and in 

 the stegocrotaphic condition; nares, orbits and parietal foramen 

 being the only openings in it. (The somewhat similar roof of the 

 Chelonians is probably secondary in character.) Except in the 



Fig. 145. — Skull oi Plateosaurns (Fraas, 'ii). -40, antorbital vacuity; co, coronoid; 

 d, dentale; /, frontal; //, infratemporal fossa; /, lacrimal; mx, maxilla; N, naris; na, 

 nasal; O, orbit; pyn, premaxilla; po, postorbital; prf, prefrontal; q, quadrate; qj, quadrato- 

 jugal; 5a, surangulare; sf, supratemporal fossa; sq, squamosal; c, zygomatic. 



Cotylosaurs and Chelonia there are one or more pairs of gaps (fossae) 

 in the roof, the more common condition being with both supra- and 

 infratemporal fossae (fig. 145), these differing considerably in size, 

 being very large in Squamata, Ichthyosaurs and Pterosaurs. Some- 

 times a posttemporal fossa is present. 



The infratemporal fossa is bounded laterally by a bar (arcade) 

 of the zygomatic processes of squamosal and zygomatic bones, the 

 quadratojugal usually intervening between the two. Medially it is 

 separated from the supratemporal fossa by a second arcade, usually 

 formed of squamosal and postorbital, but postfrontal and even zygo- 

 matic may enter it. Usually the posttemporal fossa lies between 

 parietal, supratemporal and exoccipital or opisthotic bones. The 

 lower arcade is always lacking in Squamata, only the supratemporal 

 fossa being complete. Again, interruption of the upper arcade 

 results in a single temporal fossa, and then the absence of the lower 



