REPTILES 



2I 5 



ribs and trunk vertebrae, and we see here that the girdles of 

 the limbs are brought within the shelter of the ribs, a remark- 

 able and unique arrangement. The immobility of the trunk 

 is largely made up for by the great flexibility of the neck, 

 which is supported by eight vertebrae, of which the centra 

 exhibit great variety in the shape of their ends. There is no 

 breast-bone, the presence of the plastron rendering it quite 

 unnecessary. 



As regards the skull, it need only be noted here that the 

 jaws possess a continuous sharp bony edge for the support of 

 the horny sheaths which do duty as teeth. The lower jaw is 

 jointed on to a massive quadrate bone which, as in a crocodile, 

 is firmly fused with the rest of the skull. 



The skeleton of the fore-limb corresponds pretty closely to 

 the theoretical type, except that some of the bones have fused, 

 as radiale with centrale, and carpale four with carpale five. In 

 the hind-limb there is a fair correspondence with the type, but, 

 as in Reptiles generally, there is a good deal of fusion in the 

 ankle-bones and a tendency for the ankle-joint to come between 

 the two rows of these. 



The food of the Grecian Tortoise consists mainly of vegetable 

 matter, but it also devours sundry small animals, such as worms, 

 insects, and snails. The digestive organs present no points of 

 very special interest, but it may be noted that the tongue is 

 comparatively immobile, as in the crocodile, and, as in that animal, 

 the large intestine ends in a cloaca which opens externally by 

 a longitudinal slit. 



Except as regards its flattened shape, the heart of a tortoise 

 closely resembles that of the Sand Lizard (p. 191), and there is 

 also agreement in reference to the great blood-vessels which 

 enter and leave it, each of the two aortic arches, however, 

 as in crocodiles and the larger lizards, being single instead of 

 double for a part of its course. The body is therefore, as in other 

 Reptiles, largely nourished by imperfectly-purified blood, and a 

 tortoise is a particularly good example of the sluggishness and 

 cold-blooded condition entailed by this arrangement. It also 

 exhibits in a very marked way the great tenacity of life which 

 distinguishes cold-blooded vertebrates when compared with birds 

 and mammals. 



The breathing-organs agree in most respects with those of 



