INTRODUCTION. 1X 
important portions of their organization. If, with Cuvier, 
and most other Zoologists, we include the amphibious 
group in this class, these discrepancies are still more re- 
markable ; but even restricting our view to the Reptilia 
proper, they are sufficiently striking ; and a slight glance 
at the general structure of two of the orders will exhibit 
them in a very obvious point of view. 
In the Chelonians, or Tortoises, and in the Ophidians, 
or Serpent tribe, the extremes of these different types of 
organization are exhibited. In the common Kuropean 
land Tortoise, Testudo Greca, which may be selected as 
a familiar example of the former group, the whole struc- 
ture of the skeleton is brought into the most compact 
and solid state. The bones of the cranium and face are 
consolidated into a single and immovable case, with 
searcely the vestige of sutures showing the separation of 
the different centres of ossification upon which it has 
been formed; there are no teeth, but the margins of 
the upper and of the lower jaw are covered by a horny 
beak, the latter being received into a groove of the former, 
and thus closing like the lid of a box; then the whole 
of the dorsal vertebre, the ribs, the bones representing 
the sterno-costal cartilages, and the broad united sternum, 
are altogether compacted into a case of bone, without any 
separation between the parts of which it is composed. 
The anterior and posterior extremities are fully developed, 
but, instead of being placed exterior to the thorax, they 
are all of them contained within its cavity, and even the 
bones of the feet are only extended beyond the horny box 
which protects them, when the animal is employing them 
in progression. 
What a contrast to this solid and compact structure 
is exhibited by the form of the lithe and tortuous Ser- 
b 
