THE LACEETILIA. 



189 



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

 tJie parietals and the frontals. 



Fig. 69. — The skull of Oi/elodus, entire and longitudiQally bisected. 



In the principal group of the Iiacertilia, a column-like 

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

 by any means, confounded with the stapes, to which the same 

 name is qfteu 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 '•'■ Kionocrania" or " column skulls." This coliir 

 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 pterygoid, in some Che 

 Ionia. 



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

 the side-walls of the skuU, 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 prootic 

 bones enter. Each quadrate bone is articulated with the outer 



