252 FOSSIL REPTILES. 



The Fossil Tortoises. 



We shall begin with a brief and rapid survey of the osteology 

 of the living species, and then proceed to the fossil. 



The sub-genera of the tortoises differ much more in the 

 head than those of the crocodile. In the Land-To rtoises, 

 such as the great Indian tortoise, the head is oval, and obtuse 

 in front. The interval between the eyes is wide and gibbous. 

 The nasal ^aperture is large, of greater height than breadth, 

 and inchning a little back. The orbits are large, almost 

 round, enframed on all sides, directed sideways and a little to 

 the front. The parietal region of the cranium sharpens behind 

 into a large and very salient occipital spine, and has on each 

 side two very large temporal fossa, under which are two enor- 

 mous ossa tympani. Behind these last, and a little above, 

 are two bulky mastoid protuberances, and under them are the 

 apophyses, which serve for the articulation of the lower jaw. 

 These apophyses descend vertically, and do not go backward 

 as in the crocodile. Below, the basilary region is plane, the 

 palatine concave. At the anterior part of this last, the osseous 

 back-nostrils open, the palatines having no palatine floor, and 

 the palatine portion of the maxillaries being grooved as far as 

 the anterior fourth part of the muzzle. This disposition is 

 rendered necessary by the manner in which the tortoises 

 respire, and which as much resembles that of the frogs as it 

 differs from that of the crocodiles. 



The occipital region, on the whole, is vertical, although the 

 occipital spine, the masto'idean protuberances, and the articu- 

 lar condyle of the head, which is a very salient tubercle, 

 render it very unequal. 



The first remarkable trait in the composition of the head of 

 tortoise is, that there are no bones of the nose. 



In the fresh animal, the external osseous nostrils are con- 

 tracted by cartilaginous laminae which represent these bones ; 

 but in the skeleton, immediately at their upper edge, is found 



