In the Land-Tortoises the bone analogous to the astragalus is larger and thicker ; and the fibular bone on the analogue of the heel is smaller. The four other bones exist, and that here called the meta tarsal of the little toe seems to make up the suite by its position and figure. It sometimes carries a vestige of a toe formed of one piece, which seemed to Cuvier to be wanting in many species. The meta tarsal of the great toe is very short and not flattened ; the others are longer. None of the four existing toes has more than two phalanges.
The tarsus of the Fresh-Water Tortoises is nearly the same, except that the fibular °aside, or calcaneum, when it is not united to the astragalus, is larger; that the ossicle which serves as a vestige of the little toe is longer ; and that the three toes which succeed the great toe have their phalanges very distinct.
In the tarsus of the Trionycea the fibular bone descends outside the three cuneiform or wedge-shaped bones, and carries half the head of the third metatarsal and the whole of that of the fourth. At its external border a large square bone adheres, that about which Cuvier expressed a doubt whether it was a metatarsal bone or one out of the rank. It carries the fifth metatarsal on the first phalanx of the little toe ; but in this case the little too would have three. It is true, Cuvier adds, that the fourth toe has four, without counting its meta tarsal. The great toe has two, and the two succeeding toes three each. In all three the last is large, wide, and pointed to carry a claw. In the fourth and fifth toe this last phalanx is very small and without a claw.
In the Mat: meta (Chelya) the fourth toe is, like the two preceding, composed of three phalanges, and armed with a claw ; the fifth also has three phalanges, and it would even have four if one regarded the bone as to which Curler has expressed his doubts as a tarsal bone; but the last is very small, cartilaginous, and without a nail. The tarsus is the same as in Trionyx, with this difference that the analogues of the astragalus and the calcaneum are divided transversely each into two bones ; so that what is detached from the calcaneum forms a fourth cuneiform bone for the fourth metatarsal, and that which is detached from the astragalus is a true seaphoid, which carries the first three cuneiform bones.
Muscular System—We have seen that the shoulder-blade is inter nal in the tortoises, that is, it is placed on the inside of the ribs ; the muscles, consequently, of the heed and neck, instead of being attached upon the ribs and spine, as in the other Vertebrate, are attached beneath them ; the same observation holds as to the bones of the pelvis and the muscles of the thigh ; so that, to use euvier's expression, a tortoise may be termed, in this respect, " un animal retournd "—an animal turnea inside out, or rather, so to speak, outside in.
The progressive motions to be accomplished by the bony and mus cular apparatus of the tortoises are those of walking and swimming or paddling.
The walk of a tortoise is proverbially slow, such as might be expected from a reptile whose limbs are so imperfectly developed. Short, and placed at a great distance from the centre, they form a sort of short crutches, calculated to drag the unwieldy body gradually along, and if the animal be turned on its back it becomes almost helpless. The feet are little better than stumps, the toes being only indicated externally by what may be termed a collection of hoofs, placed, as in the elephants, on the circumference of the apology for a foot, and which serve, so to speak, as a sort of grapplings to hold on the surface of the ground and drag the armed trunk onwards. We hardly need add that progression in a vertical direction is impossible; but many tortoises can burrow with some difficulty.
Nor is this slowness out of place : the preservation of the animal is provided for by the very strong bony carapace and plastron pro tecting the whole body, and only suffering the head, tail, and four feet to be protruded from its anterior and posterior part and its four angles ; these protruded parts eau be withdrawn into the shell upon the approach of danger, and the animal then rests secure in its portable arched castle, leaving the enemy to the hopeless task of besieging n garrison that can remain for months without food. A large Land Tortoise can defy the whole animal world except man, from whom nothing is safe.
The most complete defence is made by the Box-Tortoises ; for in them the pieces which form the sternum are moveable, and may be compared to doors or hinged lids, which shut upon the carapace and thus form a sort of closed coffer in which the head, neck, tail, and feet, in short, the only exposed parts, can at will he inclosed far more securely than a snail in its shell.