SIDE-NECKED TORTOISES. 89 
of S-necked or Cryptodiran tortoises, but since there are also certain features 
by which the skulls and shells of the two groups can be identified, it is im¬ 
portant that these should be noticed. As regards the skull, this is distinguished 
in the first place by the tympanic ring surrounding the aperture of the ear being 
complete, as may be seen by comparing the accompanying figure with the one on 
p. 47, and also by the circumstance that the lower jaw articulates by means of a 
LOWER AND SIDE VIEWS OF SKULL AND UPPER AND LOWER ASPECTS OF LOWER JAW OF 
greaved tortoise. (From Gray, Proc . Zool . Soc ., 1870., 
knob-like condyle with a corresponding cavity in the quadrate-bone, whereas in the 
preceding group the positions of the condyle and cup are reversed. The shell, 
which is always fully developed and forms a solid box, presents the peculiarity that 
both the carapace and the hinder 
part of the plastron are immovably 
welded to the bones of the pelvis; 
its upper and lower moieties thus 
having a bond of union which is 
totally lacking among the S-necked 
tortoises. Further, the vertebrae of 
the neck are furnished with pro¬ 
jecting lateral or transverse pro¬ 
cesses, which are absent from the 
latter group. 
In addition to these absolutely 
characteristic features, there are cer¬ 
tain other points connected with the anatomy of the side-necked tortoises which 
demand a brief notice. With the exception of one species, which lacks horny 
FRONT FORTION OF THE PLASTRON OF A SIDE-NECKED 
TORTOISE, WITH THE HORNY SHIELDS REMOVED. 
The thick lines indicate the boundaries of the shields. 
