the Uomolo(jies of the Lizard's Skull. 89 



That it is not a squamosal is rendered almost certain by 

 the facts : — 1st. That it does not touch the paroccipital as 

 the scjuamosal docs in every known reptile with a skull with 

 a fenestrated temporal rcf^ion, and in many Cotylosaurs and 

 all Clieloiiiu ; and 2nd. That its method ol: articulation with 

 tlie juj^al is tiie exact reverse of that which always occurs 

 bi'iwccu tlic scjuainosal and the jugal. 



Tiiat the upper temporal bone is not a tabular, as Willis- 

 ton and Broom believe, is, 1 think, shown by the following 

 considerations : — In all reptiles in w liich a tabular is certainly 

 known (Cotylosaurs and Therapsids) it lies on the extreme 

 back of the skull, in the latter group standing vertically 

 behind the overlapping processes of the squamosal and 

 parietal. No type is known in which it overlaps the front 

 face of the outer wing of the parietal. The close relation- 

 ship of the inner bone of lizards v\ith the end of the par- 

 occipital, which, in the exaggerated state in which it occurs 

 in Mosasaurs, was the origin of Williston and Broom's view, 

 is of no decisive importance, because of the very close and, 

 in fact, identical form of connection between the squamosal 

 and paroccipital in such diverse types as the Therapsids and 

 Sphenodon. The extension of the squamosal down between 

 the pro-otic and paroccipital in Mosasaurs seems tome to be 

 a specialization produced to meet the necessity of strength- 

 ening the support of the quadrate in very large and powerful 

 carnivorous animals. 



It will be noticed that the view of the homologies of 

 these bones which I have supported above will necessitate 

 the belief that the lizards have always had a single temporal 

 fossa, and that their present curious arrangement results 

 from the gradual reduction of a formerly broad temporal 

 arch, the processes culminating in the upw ard retreat of the 

 quadrato-jugal, to allow of the freeing of the quadrate. 

 Williston, from his study of the skull of the remarkable 

 Early Permian reptile Acroscelis, has expressed his belief 

 in the primitively one-arched nature of the lizards, and this 

 view was also held at one time by Baur. The most im- 

 portant argument against it — the presence in lizards of a 

 ligament connecting the distal end of the quadrate with the 

 jugal, which may be plausibly interpreted as representing a 

 lower arch which has disappeared — may, perhaps, be ansv\ered 

 by pointing out that such a connection is almost a mechanical 

 necessity for the support of the quadrate, and is hence quite 

 likely to have been newly formed after the development of 

 the streptostyly. 



