b CHELONII. 



but in the turtle it is covered with four square peculiar shields; 

 and there is placed at each end of this suture a small plate. 

 The front one of these is called from its position the axillary 

 shield, {scid. axillare), and the hinder the inguinal shield, 

 {scut, inguinale.) 



The legs are usually thick and short ; but the feet offer 

 considerable variation, conformable to the habits of the ani- 

 mals. In the land tortoises the toes are very short giving 

 the feet a clublike appearance, and they are armed with short 

 blunt claws ; while in the fresh water tortoises the fingers are 

 elongated and flexible, the space between them is more or 

 less hlled up with a web, and they are all generally provided 

 with sharp claws. In the genus Trionyx, however, as in the 

 crocodiles, the two outer toes are clawless. It is in the 

 marine turtle that the fingers gain the maximum of elonga- 

 tion, and become united together by a covering of thick coria- 

 ceous skin into a compressed fin, which is sometimes armed 

 with short blunt claws. The tail is generally short and thick, 

 but in one species it is long and crested on its back, like that 

 of a crocodile. When the animal is at rest it is generally 

 bent on one side under the edge of the upper shell. 



The heart is composed of two auricles and one double celled 

 ventricle ; the blood of the body enters the right auricle, and 

 that of the lungs the left ; but the two kinds ot blood are more 

 or less completely mixed in passing into the ventricle. 



The lungs are very large, and placed in the same cavity as 

 the other viscera ; but the peritoneum covering them is 

 thickened and assumes the appearance of a diaphragm. 



The jaws ate destitute of true teeth, but are usually covered 

 with a horny skin, often denticulated, the upper one covering 

 the lower like the lid of a box. The tongue is short, and 

 covered with long papillae ; the stomach is simple, and the 

 intestines moderately long, and sometimes furnished with a 

 coecum. The bladder is large. The penis of the male is 

 simple, rather large, and channelled. The eggs are covered 

 with a hard shell, and the young, when hatched, are marked 

 with a large umbilical slit in the centre of the sternum, which 

 soon disappears. 



The age of a specimen is best determined by the solidity 

 and completeness of the ossification of the bones of the shell, 

 and by the smallness or indistinctness of the areola compared 

 with the size of the shields. 



It is very difficult to determine the sex of these animals 

 externally. Perrault, and most naturalists since his time. 



