But this slowness is confined to the Terrestrial Tortoises ; for the aquatic species swim with great facility on or below the surface ; and Chelone and Sphargia for instance, with rapidity. But the well developed flipper that enables the Marine Tortoise to oar its way with swiftness, is even a worse organ for-land progression than the clumsy foot of a Land-Tortoise. Not but that they will shuffle back to the sea, which they have only occasion to leave in order to deposit their eggs, at s good pace, and they will deal heavy blows with their flippers to those who attempt to stop them (for they, as well as the Land Tortoises, are very strong), as those who have been foiled in turning turtles, have known to their cost.
But however powerfully the muscles which act upon the head, tail, and extremities are developed in this order of reptiles, those of the abdomen, as might indeed be expected, have little extent, and those of the ribs, as might also be divined, are non-existent ; for nature does nothing in vain : but the square muscle of the loins, whose principal office in mammals is to move the lumbar vertebra, acts in the tor toises, which have those vertebrae fixed, in another direction, and is employed in drawing up the moveable os ilii ; and the straight muscle (rectus abdominia) which extends from the pubis to the sternum, moves the whole haunch in the greater part of the Teatuelinata.
Digestive System.—The Chelonia have no teeth, although there are often a median groove and denticulated projections and hollows; but the mandibles are covered with a horny case, as in the birds. Tho Chtlydes and the Trionyeee, though they have the horny covering, have the mouth furnished with soft skin so as to form a kind of lips. The muscles that work the lower jaw, which is the only moveable one, are very powerful in many of the species ; and the force with which the great Turtles and many other Clielonians grasp n solid body in their vice of a mouth is prodigious. The Chetydes are the only Teatittlinata which have the jaws flat and the gape of the mouth very wide.
The food with which the Chelonia have to deal is various, and there are modifications in the digestive organs accordingly. The Melones and Teattufiru-s generally prefer a vegetable diet.. The Tri cares and Chelrles prey upon fishes and small aquatic birds ; and the Entycles attack the weaker *nimbi, such as Crustaceans, Insects, NVorma, and Mollusks.
These aliments are submitted in the Terrestrial Tortoises and in the Chelonians to the trenchant horny bill, well fitted to mince up vegetable fibre, assisted by the tongue, which draws the food into the mouth and the horny grooves and hollows of the jaws ; the Trionyees and Entiales seize their living prey in their sharp-edged beaks and tear it to pieces with the cutting and pointed claws of their fore feet : some of these dart out their head and long neck upon their prey from an ambush ; or, stealing along like the cats till they come within roach, suddenly extend their destructive apparatus with unerring aim. The Mirk., whose fleshy jaws are flat, swallow their prey whole, and in this respect, as well as in the general conformation of the head and the os hyoides, they resemble the Toads, and especially the l'ipas, like which they are obliged to be content with a victim of small dimensions snited to the calibre of their mouth, which is, in truth, autneiently large. They are said never to adze their prey till they are satisfied by its motions that it is alive, for they never feed on carcasses.
The tongue of the tortoises is fleshy, like that of the parrots, and its nervous papilla are very distinct. The msophagua is short, and in the Chelonians is furnished internally with a number of close-set car tilaginous points, directed so as to prevent the regurgitation of the food towards the stomach, which has a transverse position. The intestines are long ; the cloaca is situated beneath the tail, and rounded, and internally is found the orifice of amnia which terminate in the cavity of the peritoneum. The liver is voluminous, forming two masses or lobes placed transversely below the heart and in front of the junction of the (esophagus with the stomach. The pancreas is a very large gland, and the spleen is rounded, median, and situated at a considerable distance from the liver. The chyle is tranitlucid and aqueous in the vegetable feeders, but of a white and milky tint in those species which feed on animals.
The power of abstinence in tide order of Reptiles is very great.. Messrs. Dum6ril and Bihron state that they have seen a Long-Necked Ernys remain more than a year without food ; and Mali kept Land Tortoises fasting for eighteen months.