8 TESTUDINATA. 



ORDER I. TESTUDINATA. 



( ToHoises.) 



The appearance of an animal of this Order 

 will naturally recal to the mind the mailed Arma- 

 dillos among the Edentate Mammalia, as the 

 Sauria will remind us of the Pangolins. The 

 Tortoises are readily distinguished from other 

 Reptiles by their body being inclosed in a double 

 buckler, which admits only of a partial protru- 

 sion of the head, tail, and limbs. The bones of 

 the skeleton, though essentially the same as those 

 found in the preceding classes, are strangely modi- 

 fied. If we remove the convex shield, called the 

 carapace, that covers the upper part of a Tortoise, 

 and turn it up, we shall find on the inner surface 

 the vertebral column imbedded into an immov- 

 able piece, and the ribs flattened and widened so 

 as to touch each other at their edges. The verte- 

 brae of the neck and of the tail alone are free. The 

 lower plate or plastron, in like manner, is com- 

 posed of pieces representing the breastbone or 

 sternum, united by sutures. 



The external surface of these shields is covered 

 with a series of plates of a horny (or sometimes 

 leathery) texture, of regular but varied forms, 

 united at their edges, but sometimes overlap- 

 ping posteriorly. The shoulder-blade and all the 

 muscles of the arm and neck, instead of being 

 attached to the exterior of the ribs and spine, 



