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 46 form a case or box within 
ey 
\ joan 
4 
Rig. 444._Skeleton of European Tortoise, with the plastron or under sheli removed, 
—After Owen. 
which the turtle can retract its head and limbs and tail. 
Owing to the presence of the carapace, the dorsal vertebra 
are immovable, and the ribs are quite rndimentary. 
The bones of the ventral shield or plastron are usually 
