CHELONIAN HEPTILES. 



417 



interesting to remark that tlie occipital condyle, 

 which is situated at the lower margin of the great 

 aperture, thougli presenting a single convex surface, 



yet has that surface evidently 

 divided into three parts ; the 

 two upper portions being la- 

 teral, and the lower portion 

 in the middle. These three 

 articular surfaces are seen im- 

 mediately below the central 

 aperture, f, in Fig. 215, which exhibits the skull of 

 the Testudo mydas, viewed from behind. Although 

 closely approximated, a faint line of denmrcation, 

 which divides their surface, indicates an incipient 

 tendency to separate. We shall find that in the 

 further steps of developement which occur in the 

 higher classes, this separation actually takes })lace 

 by the obliteration of the lower articular surface, 

 and the transfer of the two lateral surfaces to the 

 condyloid processes, arising from the developement 

 of the leaves of the occipital bone. 



The singular conformation of the bones of the 

 head in the turtle has been considered as affording 

 additional evidence in support of the theory that 

 these bones were originally vertebrae. The brain 

 of this animal is exceedingly small ; and yet the 

 skull, when viewed from above, presents an appear- 

 ance of great breadth, as if it enclosed a cavity of 

 large dimensions. But if we look upon it from 

 behind, as is shown in Fig. -215, we soon discover 

 that the real cavity in which the brain is lodged, 

 and to which the aperture at f leads, is very small, 

 only just admitting tiie end of the finger, and that 

 the broad plates of bone, p, v, which form the upper 



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