a, eo . oe” | a 
OF SOUTH CAROLINA. 25 
Class Reptilia. 
Sauria —Alligator, Lizard. 
Chelonia — Turtle, Terapin. . 
Ophidia —Rattlesnake. 
Batrachia —F'rog, Salamander. 
Ichthyodea— Proteus, Siren. 
Characters of the Class.—In Reptilia the cranium is articulated by means of a single condyle ; 
which in some of the orders presents a disposition to divide, and in Batrachia the lateral occipitals 
terminate in two articular tubercles. ‘The cranial elements are not firmly united, as in other 
vertebrata, but generally remain separate. 
The lower maxille are composed of two pieces, which in Sauria are united by suture, but in 
Chelonia are firmly anchylosed and form one solid piece. Mach of these is composed of six bones, 
a character that enables the Palzontologist to distinguish the lower jaws of Reptilia from all 
others. ‘The lower maxille articulate with the cranium by means of the intermediate os quadratum. 
The teeth are conical and composed of a pulp cavity, surrounded by dentine. They are 
indented on the surface by irregular strie, and in addition to these, two prominent acute ridges 
mark the anterior and posterior sides of the crown. The root or fang is always single. In the 
alligator the hollow of the root is occupied by the young tooth, which, when it comes in contact 
with the sides, produces a notch in the old tooth. The alligator differs from the crocodile proper, 
in having the upper jaw larger than the lower. When the mouth is closed the lower teeth fit into 
pits in the upper jaw; whereas, in the crocodile, the upper and lower series of teeth meet like 
those of a trap. In some fossil teeth a succession of teeth may be observed fitting closely, like a 
series of hollow cones, one over the other. 
In Batrachia the microscopic character of the teeth is very curious and characteristic. 
The vertebra of reptiles are characterised by that peculiar mode of articulation called “ ball and 
socket” joints, consisting of a convex and concave surface adapted to each other. 
In Sauria the concave surface is placed anteriorly and the convex posteriorly ; but in Batrachia 
this order is reversed—the concave part being turned backwards, and the convex surface before : 
while in Ichthiodea both ends are concave, like those of fishes. The crocodiles have about sixty 
vertebra, of which seven are cervical, twelve dorsal, five lumber, two sacral, and the rest are 
caudal. ‘The alligator, however, has sixty-eight, the additional ones being found in the tail. The 
neurapophyses are united by suture to the centrum, but the suture is often obliterated by age. 
‘The ribs in crocodiles are bifurcated at the proximal end, and articulate with contiguous vertebre. 
The bones of the extremities, having no medullary cavity, are solid in recent species. 
The Chelonians present a most strange modification of the prevailing characters of vertebrata.— 
Instead of the usual internal skeleton we find long shields, enclosing the body on all sides. The 
upper one, which is called the carapace, is composed of the coalesced ribs, vertebre, and processes. 
The cervical and caudal vertebra show the true reptilian characters; and even the ribs may be 
seen united to two adjacent vertebre, and one or two of the first are bifurcated. ‘Towards the 
extremities the broad costal plates terminate in narrow points like true ribs, and the union of these 
with the surrounding marginal plates or scutes affords some useful characters. 
In the land and fresh water species, with the exception of Trionyx, these points are anchylosed 
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