TORTOISES AND TURTLES. 



105 



it is situated within the cavity enclosed by the ribs and 

 shell. Similarly the haunch-bones, which in all other 

 living animals lie close to the outer surface of the body, 

 are likewise shifted within the cavity of the ribs and 

 shell. To reach the shoulder-blades and haunch-bones 

 the bones of the arm and leg are bent in a manner 

 quite peculiar to this group of reptiles, so that they 

 are readily recognised when found in a fossil state. 

 We should, however, mention that the above peculiar 



FIG. 30. The front portion of the plastron of a Freshwater-Tortoise of the 

 Southern Hemisphere, with the horny shields j removed. The thick lines 

 indicate the boundaries of the horny shields. 



inside -out arrangement is only found in the adult con- 

 dition ; extremely young tortoises having the shoulder- 

 blades and haunch-bones situated respectively in front 

 of the first, and behind the last rib, and being gradually 

 grown over by the plates developed upon these ribs. 



One other peculiarity in the bony structure of the 

 group still remains to be mentioned. It is probably 

 well known to our readers that ordinary reptiles 

 such as crocodiles and lizards are furnished with 

 well-developed teeth, which are frequently of great 



