THE LACERTILIA. 



189 



roof of the skull in tlie course of the sagittal suture, or between 

 tJie parietals and the frontals. 



Fmx To 



!>& 



Fig. 69. — The skull of Cyclodus, entire and longitudinally bisected. 



In the principal group of the LacertiUa^ a column-like 

 membrane-bone, called the columella (but which is not to be, 

 bj any means, confounded with the stapes^ to which the same 

 name is often applied in Reptiles), extends from the parietal 

 to the pterygoid on each side, in close contact with the mem- 

 branous or cartilaginous wall of the skull. Hence they have 

 been called "^zonocrama," or " column skulls." This colu- 

 mella (Fig. 69, Co) appears to correspond with a small inde- 

 pendent ossification, which is connected with the descending 

 process of the parietal and with the pterj^goid, in some Che 

 Ionia. 



In the great majority of the Lacertilia (as in the Chelo7iia), 

 the side-walls of the skull, in the region of the ear, are pro- 

 duced into two broad and long parotic processes, into the com- 

 position of which the opisthotic, ex-occipital, and prootio 

 bones enter. Each quadrate bone is articulated with the outer 



