ANATOMY OF THE TURTLE. 



505 



ing forms, yet they have some affinities with the Batrachia. 

 They are distinguished from the other reptiles by the shell, 

 the upper part forming the carapace, and the lower the 

 plastron ; these two parts unite to form a case or box within 



Fig. 444. Skeleton of European Tortoise, with the plastron or under shell removed 

 After Owen. 



which the turtle can retract its head and limbs and tail. 



Owing to the presence of the carapace, the dorsal vertebras 



are immovable, and the ribs do not move upon the vertebra?. 



The bones of the ventral shield or plastron are usually 



