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 caraiJace, and the lower the 

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



Pig. 444.— Skeleton of European Tortoise, with the plastron or under shell removoA 

 —After "^ 



.fter Owen. 



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



Owing to the presence of the carapace, the dorsal vertebrsa 



are immovable, and the ribs do not move upon the vertebrse- 



The bones of the ventral shield or plastron are usually 



