AMATOMY OF THE TURTLE. 



505 



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

 They are distinguished from the otlier reptiles by the shell, 

 the ujiper part forming the carcqmce, and the lower the 

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



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

 —Alter Owen. 



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



Owing to the presence of the carapace, the dorsal vertebrae 



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



The bones of the ventral shield or plastron are usually 



