THE SKELETON OF REPTILES 



23 



doubtless greater brain power have rendered unnecessary or useless 

 the older kinds, just as modem methods and modern arms have 

 rendered useless the coat of mail of the Middle Ages. 



The old reptiles had a continuous covering or roof for the skull, 

 pierced only by the openings for the nostrils in front — the nares — 

 the orbits for the eyes near the middle, and a smaller median open- 

 ing back of them for the so-called "pineal eye." The temporal 

 region, that is, the region back of the orbits on each side, was 

 completely roofed over by bone for the support and protection of 

 the jaw muscles. In later reptiles this region has been lightened. 



Fig. 7. — Edaphosaurus, a theromorph reptile from the Permian of Texas. Skull 

 with single temporal vacuity. 



either by holes that pierce it or by the emargiiiation of its free 

 borders, as in the turtles. The openings have occurred in different 

 ways, and with the loss of different bones in various lines of descent. 

 In one large group of reptiles, comprising the pterodactyls, dino- 

 saurs, phytosaurs, crocodiles, and rhynchocephalians, there are 

 two openings on each side, called the supratemporal and lateral 

 temporal vacuities. In another still larger group there is a single 

 vacuity on each side, all members of which it has been thought were 

 markedly related to each other. Some of these, the lizards, snakes, 

 and mosasaurs, the ichthyosaurs, and probably the proganosaurs. 



