They are divided into two groups:—
I. Crocodilidæ, having the lower canines fitting into a notch in the edge of the upper jaw.
II. Alligatoridæ, having the canines fitting into a pit in the upper jaw.]
Crocodiles.
The Shielded Saurians, as Duméril designates the largest of living species of that order of reptiles, have the body depressed, elongated, and protected on the back with a solid carinated shield or buckler; the tail longer than the trunk, compressed laterally, annulated and crested above; having four very short feet; the toes of the posterior feet united, or web-footed, each foot having three claws only; head depressed and elongated into a muzzle; the gape of the mouth extending back beyond the skull; tongue fleshy, adherent; teeth conical, simple, hollowed at the base or towards the root, unequal in length, and in a single row. Such is a brief summary of the family by Duméril and Bibron.
If the Eagle is the king of the air, the Tiger and the Lion the tyrants of the forests, and the Whale the monarch of the deep, the Crocodile has for the exercise of his undisputed control the maritime shores of tropical seas and the borders of tropical rivers. Living on the confines of land and water, this formidable reptile is at all times the scourge of those human beings who are compelled to reside near its haunts. Much larger than the Tiger, Lion, or Eagle, the Crocodile surpasses all terrestrial animals, with the exception of the Elephant, Hippopotamus, and some Serpents, in its power of destruction.
Crocodiles have the head depressed and elongated into a muzzle, in the front of which the nostrils are seen close to a fleshy tubercule, and furnished with movable valves. The mouth opens up to the ears; the jaws are of commensurate length, and are armed, as we have seen, with conical-pointed teeth, bent back, and disposed in such a manner that when the mouth is closed they pass one under the other. These teeth are implanted in a single row, and continually maintained in a good condition by an organic system which ensures their immediate reparation. In short, each tooth is hollowed at the base in such a manner as to form the cell or sheath of another tooth of a larger calibre. The new tooth, which presses on, exercises a sort of absorption upon the base of the old hollow tooth, so that the first is developed while the second is decaying. In some species the front teeth of the lower jaw are so long and sharp that they perforate the edge of the upper jaw and appear above the muzzle when the mouth is closed. The lower jaw alone is movable, and that only in a downward movement. The mouth is without lips, consequently, whether walking or swimming, the teeth of Crocodiles are always visible.
This formidable conformation gives to the Crocodile an aspect at once terrible and alarming, which is increased by two wicked-looking eyes placed obliquely and close together, surmounted by a kind of eyebrow. The tail of these animals is very long, as thick as the body at the junction, and in shape it is flat, like an oar; this enables them to steer through the water like a fish, and to swim with rapidity. They have four short legs, of which the hinder have toes, united by a natatory membrane, and only three claws to each foot. The skin is coriaceous, thick, and resistant; being also protected by very thick knots intermingled with plates of different size, according to the parts of the body they protect. On the skull and face the skin adheres closely to the bone, and there is no trace of scales.
Nature has provided for the safety of these animals by covering them with a cuirass, the resistance of which is proof against almost everything. Thus the scales which defend the back and the upper part of the tail are square, and form hard transversal bands possessed of great flexibility, which prevents them from breaking. Down the centre of the back there is a hard crest, which adds to the strength of their armour. This cuirass is in many points proof against a bullet from a gun. The plates which cover the belly, the upper part of the head, neck, tail, and legs are also arranged in transversal bands, but less hard, and without crests. It is at these weaker and consequently vulnerable parts that those inhabitants of the waters which are enemies to Crocodiles manage to attack them successfully.
The general colour of the Crocodile is a dullish brown, with sometimes a shade of green along the back; the head and the sides are marked with green, or at least they have a greenish tint, with blackish spots; the under part of the legs and belly are of a yellowish grey. All these shades, however, vary with age and sex, and the nature of the water in which the animals live.