THE LACERTILIA. 



219 



The skull of the Lacertilia resembles that of the Chelonia 

 in the development of an interorbital septum (except in 

 the Ainiyhisiceme), and in the absence of alisphenoids, or of 

 any complete ossification of the prespheuoidal or orbito- 

 sphenoidal regions. The premaxiUse and maxilliB are firmly 

 united with one another and with the skxiU., and there are 

 two vomers. An unossified space, the parietal foramen, 

 iisually remains in the roof of the skull in the course of the 

 sagittal suture, or between the parietals and the frontals. 



FiR. 69. 



Jit 



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



In the principal group of the Lacertilia, 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 often applied in Reptiles), extends from the 



