Shielded Reptiles. REPTILES. Land Tortoises. 
68 
its two extremities, the head and tail. The plastron 
is equivalent to the breast-hone or sternum in birds 
and mammals, and is composed of nine pieces, which 
in general are firmly united together — fig. 21. It covers 
all the lower part of the belly of the animal, is solid 
in the land and most of the fresh-water species, but 
varies very much in form and structure. Round the 
edge of the carapace there are a series of bones joined 
together, ivhich represent the cartilages which join the 
ribs to the sternum in birds, &c. From this structure 
Fig. 21. 
there results, of course, a complete immovability in 
all these parts, and an immense degree of strength. 
Their head is generally rather small, and of a flattened 
form, and the jaws are covered with a hard, sharp, 
horny beak, the lower portion of which shuts within 
the upper. This structure supplies the place of teeth, 
and the portions of food are cut or snapped otf on the 
principle of shears. Though they do not bite very 
readily, jmt, when they do, they bite very severely. 
There is no possible means of making them let go 
their hold. Even killing them will not always suffice. 
They will retain the piece unless the jaws be completely 
broken. So forcible, indeed, and so violent is their 
bite, “ that I have known,” says Mr. Bell, “ a stick of 
half an inch in diameter at once snapped asunder by 
the jaws of a Snapping Turtle ; and a specimen of 
Trionyx, lately in the possession of Mr. Cross of the 
Surrey Zoological Gardens, snapped off the finger of a 
sailor when on his voyage to this country.” The 
limbs of tortoises and turtles present a great contrast 
to that of most other vertebrated animals. They are 
short and thick, and in all are far removed from the 
centre of gravity. The form and structure of the feet 
differ much in the different groups, according to their 
habits of life. In the Land tortoises they are too short 
to be able to sustain for a long time the weight of the 
body, or to elevate it above the level of the ground 
sufficiently to make locomotion easj'. They are clumsy 
and club-shaped, and these animals therefore only drag 
themselves slowly along the ground, their plastron or 
breast-plate almost pressing upon it ; and as they move 
along, their walk is tottering, uncertain, and extremely 
slow. The marine species, or Turtles, and those which 
live in rivers, have their feet changed into regular 
paddles or oars, and endowed with great muscular 
power. They are thus able to swim well, and their 
motion through the liquid element, in which they live, 
is rapid and not without grace. Those species which 
live in ponds are intermediate between the other two 
groups, and have the toes webbed and the claws sharp. 
They are thus able to move along both in the water 
and on the land ; whilst the Land tortoises would perish 
in the water ivere they to live in its immediate neigh- 
bourhood, and are consequently only found on dry 
land. Tlie neck in tortoises and turtles is generally 
cylindrical and capable of great extension, .and though 
the skin is almost always covered with small scales, 
which are separate and hard, it is the most defenceless 
part of the animal, and tliat in which it may most 
easily be killed. The legs and feet are generally 
covered with scales also, which serve as a considerable 
protection to them from accidents or injury ; and the 
texture of this skin is so solid, that the sharpest instru- 
ments can with difliculty penetrate it. The senses 
possessed by these creatures are in general far from 
being acute. The range of their sensations may be 
said to be confined to the strictest limits of necessity, 
or, in other words, merely to what is indispensable tor 
the purposes of self-preservation and reproduction. 
LAND TORTOISES {Testudinidce). 
The land species are all comprised in one family, 
Testudinidce, or Tortoises properly so-called; and of 
all the Chelonia are those which have their shell 
composed of the thickest and heaviest pieces. In 
the adult state it is covered with horny, concen- 
trically-grooved shields, which are marked with a 
permanent areola ; and thus the shell is never smooth 
on the surface, as is the case with marine turtles, 
&c. The head is in nearly all the species pro- 
portionally of the same size; in general it is short, 
thick, and quadrangular. T'he eyes are placed laterally 
and on the same level with the head. The eyelids are 
cleft obliquel 3 ^ in such a way that the anterior angle is 
nearly of the same height as the nostrils, whilst the 
hinder angle is a little higher. The nostrils open at 
the extremity of the muzzle. The tongue is thick and 
covered on the upper part with papillce. The horny 
sheaths which cover the bones of the jaws are very 
solid and sharp-cutting, or, in some, more or less 
toothed ; and the jaws themselves close like the lid of 
a box, and can onl}' act in one way, like the blades of 
scissors. The head and neck can alwaj's be withdrawn 
within the shell. But the most distinctive character 
of the Land tortoises resides in the structure of the feet. 
The hinder and fore legs are nearly or quite of the 
same length; the foot is hard, and of a truncated stump 
form, like that of the elephant. When they w'aUr, or 
as it w'ere drag themselves slowly along, this foot is 
turned obliquely outwards, for it never rests completely 
on the ground, the claws in fact forming the sup- 
