THE TEMPORAL ARCHES OF THE REPTIL1A. 19! 



acter, but we are now quite certain that the lizards are an ex- 

 ceedingly old group, probably dating from the Permian, and that 

 they have not a few very primitive characters, such as the pres- 

 ence of pterygoid teeth ; perhaps the early forms, like those of 

 the early crocodilia, will all be found to have amphiccelous ver- 

 tebrae. However, whether or not this outer plate has early fused 

 with the paroccipital beneath it, and has remained persistent in 

 the lizards, I will not say, but I do believe that the bone corre- 

 sponds to the paroccipital. 



The archosaurian type of arches is one easily derivable from 

 the Rhynchocephalia a conjoined postfrontal and postorbital 

 uniting posteriorly with the squamosal, to form an upper bar ; 

 and a quadratojugal intercalated between the jugal and quad- 

 rate to form the lower bar. The variations in the dinosaurs 

 (Fig. 9) and the crocodiles (Fig. 10) are not great, and doubt- 

 less a like structure will be found in the pterosaurs when this 

 part of their anatomy is better known than it is at the present 

 time. 



Returning now to the theses which headed this discussion, we 

 see : That, in the Synapsida, neither the Cotylosauria nor the 

 Testudinata have a large or any supratemporal vacuity ; that, the 

 cotylosaurs, if ancestral to the Synapsida, the Diapsida and the 

 Testudinata, cannot be properly included into a subclass with 

 any one of them ; that the turtles could not have been derived 

 from the Anomodontia, but apparently represent a distinct and 

 independent branch from the Cotylosauria, or at the least from 

 the primitive stem of the Synapsida before it had developed a 

 supratemporal fenestra ; that there is no evidence of a prosqua- 

 mosal bone in any of the Synapsida (excluding the cotylosaurs), 

 and little of the quadratojugal in the Anomodontia and Saurop- 

 terygia ; that it was the elements of the lower, not the upper 

 arch which became degenerate, leaving the mammalian zygoma 

 to be composed of the squamosal and jugal only. 



That, in the Diapsida, the prosquamosal is known to be pres- 

 ent in but two forms ; that it was an element of the lower, not the 

 upper arch ; that the arch of the lizards is the upper, not the 

 lower one, and consequently does not contain the elements of 

 that arch ; that Procoloplwii, though a primitive diapsid, had 



