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 removetl 

 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 are quite rudimentary. 



The bones of the ventral shield or plastron are usually 



