Crocodile, a genus of reptiles which, with the alligator of America and the gavial of the Ganges, constitute the family of crocodilians. Some authors elevate the family into an order, the emydosauri of Gray, the loricata of Fitzin-ger, and the rhizodonta of Prince Bonaparte, the latter including the large fossil ichthyosaurus and plesiosaurus. In the class of reptiles they are higher than the saurians, and second to the testudinata; among them are included some of the largest, most powerful, and best protected of their class. The crocodilians, including the alligator and gavials, are characterized as follows: the skin is tough and thick, and protected by firm scales, of different shapes and sizes, forming a coat of mail sword- and bullet-proof; different species have been distinguished according to their arrangement on the neck; they are square on the upper and under surfaces of the body and on the tail, large and ridged longitudinally on the back, small and rounded on the sides of the body and neck and limbs; on the head the skin is applied directly on the bone, following its eminences and depressions, and unprotected by scales, in this differing from the true saurians; the scales are thinnest below, and of a lighter color, almost white, the upper tints being greenish with dark spots, or an obscure brown.
Under the jaw, in the longitudinal folds of the skin, open the ducts of odoriferous glands, which secrete a viscid matter having a strong and disagreeable musky odor; similar pores open near the cloaca. For the details of the skeleton the reader is referred to Cuvier, Meckel, Oken, and other writers on comparative anatomy. The vertebras are concave anteriorly and convex posteriorly, and are 7 or 8 in the neck, 12 in the back, 5 in the loins, 2 in the sacral region, and from 34 to 42 in the tail; the number is the same in individuals of a species at all periods of life. The vertebrae of the neck have long articulated transverse processes, or cervical ribs, which prevent any extensive lateral motion of the neck; on the under surface of the caudal vertebra) is a series of V-shaped bones, the haemal arches, for the protection of the vessels. The ordinary ribs are 12 to 13 on each side. The sternum is prolonged even to the pelvis, and gives attachment to 6 or 7 pairs of cartilages, not extending to the spine; these serve to strengthen and protect the abdominal walls, and are represented in man by the transverse lines of the rectus abdominis muscle; the sternum is also prolonged as a point in advance of the ribs; there are no true clavicles, and the bones of the pelvis remain separate.
The lower jaw is longer than the cranium, because the condyles of the temporal bones, corresponding to ossa qnadrata, are placed considerably behind the articulation of the head with the spine, and are united to the skull as in the turtles; the gape of the mouth is really longer than the extent of the head, from this backward situation of the glenoid cavity. The muscles which move the jaws arise so far back, that they act in part upon the whole head, explaining the assertion made from the time of Aristotle to that of Cuvier, and at various times believed and disputed, that the crocodile has the ability to move both jaws; when the lower jaw is fixed upon the ground, the action of the muscles may raise the whole head, and with it the upper jaw, otherwise immovable. The jaws have no lateral motion, and none from before backward, the articulation being a simple hinge joint. There are no cutaneous lips, the teeth being visible even when the jaws are closed. The teeth are numerous, conical, isolated, unequal in size, hollowed at the base, arranged in a single row, implanted by a true gomphosis in the substance of the maxillary borders, in special alveoli directed from before backward, and provided with a kind of gum; the new teeth push up into the hollow of the old, and cause their absorption; the new teeth are larger, but the same in number at all ages.
The tongue is flat, wide, fleshy, and attached all around to the jaw bone; it is not divided at the tip, and cannot be extended, being apparent only when the jaws are separated, and forming the floor of the mouth; it cannot be used to seize or retain their prey, nor for respiratory purposes; it is for the most part smooth, except at the base, where irregularly contorted folds are prominent. The nostrils open at the end of the muzzle, near together, and may be closed by valves; their cavity forms two canals, extending along the cranium, and opening, not into the mouth, as in other reptiles and birds, but into the posterior fauces behind the soft palate, as in mammals; the hyoid bone sends upward a rounded cartilaginous continuation, which can be made prominent at the will of the animal; the soft palate hangs down to meet this, by which the cavity of the mouth can be completely shut off from the fauces; by this arrangement, when the animal is under water, with only the tip of the nose in the air, and even with the mouth filled with water, respiration can be perfectly carried on; and by the same mechanism the act of swallowing can be accomplished beneath the surface.
Unlike the saurians, this family have the external opening of the ears protected by two folds of the skin, resembling lids, by which the meatus can be closed; the opening is just behind the eyes. The eyes are very small, and provided with three lids, an upper and lower, with a third or nictitating membrane moving transversely, transparent, and evidently designed to protect the cornea and permit vision under water; the pupil is a vertical slit, and the crystalline lens almost spherical. The anterior limbs have five toes, the external two without nails; the posterior limbs are four-toed, more or less webbed, the external one without a nail; the limbs are so short that they barely raise the body from the ground, and are almost at right angles to the spine; their gait is, therefore, slow and awkward. The tail is longer than the trunk, flattened on the sides, surmounted with crests continued from the back, and serrated below; the powerful muscles of the dorsal region are carried to their greatest development in the sides of the tail, which is the principal organ of locomotion in the water.
The stomach is muscular, but in no way resembling the gizzard of a bird; in this cavity . are frequently found stones and pieces of wood, which were once supposed to be swallowed intentionally to assist in triturating the food, or for the purpose of distending the stomach during the season of hibernation which some of them undergo; it is altogether probable that such foreign bodies have been accidentally swallowed during the repasts of the voracious animal. The lungs consist of three principal cavities, communicating freely with each other; the walls are divided into innumerable cells, the fleshy compartments of which form a very intricate network, resembling the columns carneae of the heart; when fully expanded, they will contain a large quantity of air. The most interesting organ is the heart, as it shows an approach to, and as it were the connecting link with the birds. In reptiles generally the heart consists of three cavities, a ventricle and two auricles; the ventricle receiving both arterial and venous blood, and sending this mixed fluid over the system at the same time that it sends to the lungs blood of which a portion has just been received purified from them.
In the croc-odilians the ventricle has a complete division into right and left, and the circulation is so arranged that while the head and anterior half of the body receive pure arterial blood when the animal is in the air, the posterior half receives a mixed arterial and venous blood; the mingling of the two bloods taking place, not in the heart itself, but by an opening between the two aortas, a fact unknown to naturalists till the time of Meckel and Panizza. The ordinary course of the circulation would be through the venae cavae to the right auricle, thence to the right ventricle; from this more than half of the venous blood goes to the lungs by the pulmonary artery, the rest being distributed to the lower extremities through the left or venous aorta; from the lungs the pure blood comes to the left auricle, thence it passes to the left ventricle, and then by the right or arterial aorta to the head and anterior extremities and body generally, after mixture with the venous blood. In the common circulation, or when the animal is in the air, there would probably be but a trifling, if any, mixture of the bloods through the opening in the aortic wall, and during the contraction of the ventricles the pressure of the valves of the aorta) against the opening would prevent the mingling; but during the diastole of the ventricles, when the valves close to prevent regurgitation into the heart, the aortic opening would be free, and the bloods could mix in whichever direction the pressure was the strongest; the opening, however, performs its special function after the animal has been under water a long time, when there is no respiration nor pulmonary circulation, no blood in the left ventricle, and none sent through the true aorta; were it not for this opening, the head and anterior limbs, which are supplied by the right aorta, would be unprovided with blood; it has been naturally concluded that venous blood is sent through the opening from the left aorta to supply these parts.
By its four cavities the heart of the crocodilians resembles that of the birds, and also, by the mixture of the blood in the vessels, that of the fetal mammalia. Meyer compares the left aorta to the ductus arteriosus, and he believes this structure to be a temporary condition, disappearing as the animal advances in age. In the dissection alluded to above, the specimen was seven feet long, and old enough to be impregnated; the edges were firm and well defined, like those of a persistent foramen; and physiological reasons have been given why it should be permanent in this family, when the respiration ceases during submersion and hibernation. In the males the genital organs are simple; as in turtles and birds, the cloaca is longitudinal. The female alone prepares the hole in the sand in which the eggs, sometimes GO in number, are placed probably during the night; she covers them with sand and leaves to hide them from the ichneumon and certain reptiles which feed upon them; the eggs are hatched in from three to six weeks, according to season and latitude. The amphibious habits of the crocodilians are indicated by the nostrils, separation of the posterior fauces from the mouth, shape of the limbs and tail, and structure of the lungs and heart.
The crocodiles proper are distinguished from the alligators by their head being longer in proportion to the breadth, by the smaller number of teeth (30 below and 38 above, according to Cuvier), by the fourth lower tooth on each side being received into a groove in the upper jaw instead of a pit when the mouth is closed, by the dentated crest on the external border of the hind legs in most of the species, by the complete webs of the hind toes (at least the external), and by the larger cranial openings perceptible through the skin behind the eyes. Nothing is more characteristic than the narrowing of the muzzle behind the nostrils caused by the groove just alluded to, added to the perforation of the upper jaw by the first lower teeth; the plates of the nape occupy the middle portion only, a space before and behind being without them; as age advances the head becomes very rough. The species are difficult to distinguish from each other, and the variations within the limits of species are considerable. - Europe has no crocodile, nor crocodilian, in its present fauna; America has two, Asia two, and Africa one; other species are described, of unknown habitat, and of uncertain characters.
The following species will sufficiently characterize the genus: I. The common crocodile of the Nile (crocodilus vulgaris, Cuv.), one of the sacred animals of the Egyptians, is mentioned by Herodotus, and well described by Aristotle in his "History of Animals;" the latter also mentions the spur-winged plover (vanellus), which enters the mouth of the crocodile to pick out and eat the insects attached to the mucous membrane. This species has the widest jaws, 6 cervical plates, the dorsal plates quadrangular with 6 longitudinal series of moderate ridges; cranium rather flat; teeth 66, 36 above and 30 below, the longest being the 3d and 9th of the upper jaw, and the 1st, 4th, and 11th of the lower; 16 to 18 transverse rows of bony plates from the shoulders to the tail, and on the latter from 26 to 38 circles of scales surmounted by a thin, flexible, serrated crest, double for about half its length. The color of the upper surface is olive-green, spotted with black on the head and neck, and marbled with the same on the back and tail; two or three wide, oblique black bands on each flank; beneath greenish yellow; claws brown. It grows to the length of 20 to 25 ft., and possibly longer.
A variety of this (G. palustris, Less.), found in Asia, has the head rougher, the scales of the sides, flanks, and upper part of the neck convex and ridged, and the color above olive-yellow, marbled with blackish brown. A third variety (G. marginatus, Geoff.), a native of southern Africa, has the jaws narrower and elongated, the cranium slightly concave, six narrow nuchal plates, the upper parts deep bottle-green, with small brown waving lines disposed in a radiating manner. This variety grows to a large size, and is doubtless the one so often seen by Livingstone and Cumming in their journey-ings in South Africa. Livingstone says that 60 eggs have been taken from a single nest; they are about the size of a goose egg, of the same diameter at both ends, white, and partially elastic from having but little lime in their composition and a firm internal membrane. The nests are within a few feet of the water, and are used for successive years if undisturbed; the female assists the young out of the nest, and leads them to the edge of the water, where she leaves them to catch fish for themselves.
Fish is the principal food at all ages; a wounded animal, or even a man, going into a lake infested by them, is almost sure to be seized; they seldom leave the water to catch prey, but often come out to bask in the sun; they fish chiefly by night, and when eating make a loud champing noise. The natives are very fond of the eggs, eating only the yolk. The Egyptians kept crocodiles in their temples, where they were fed by the priests and ornamented with gold and precious stones; these were highly venerated by the people, and after death they were carefully embalmed and buried with great ceremony; it is very common to find mummies of crocodiles in their tombs, and many may be seen in our museums. The ichneumon, a carnivorous mammal allied to the civets, renders important service to man by destroying the eggs of the Nilotic crocodile. The common crocodile is not confined to Africa, but occurs in Asia, especially on the Malayan peninsula; it is often met with three or four miles at sea, and has been known to attack boats returning from fishing, and occasionally with the loss of human life. II. The most common Asiatic species is the double-crested crocodile (C. hipor-catus, Cuv.), so named from the two rough lines on the upper jaw extending forward from the anterior angle of each eye.
The lateral borders are irregularly convex, and deeply grooved for the lower teeth; the upper surface is very rough, especially in large individuals; the teeth are generally 66, 36 above and 30 below, the largest being the 2d, 3d, 8th, and 9th above, and the 1st and 4th below; the hind legs are as long as the trunk, the fore legs are a third shorter; the armature of the neck consists of 6 shields, 4 in a square, and 1 on each side of these, of an oval shape and strongly crested; on the back are 16 or 17 transverse rows of ridged plates, of an ovoid form; the tail has 38 or 40 scaly rings, double-crested for half its length. The color is yellowish green, with black oval spots above. It grows to a length of at least 20 ft. In Gi-roniere's "Twenty Years in the Philippines" is an account of the capture of an immense individual of this species, measuring 27 ft. in length and 11 ft. in circumference under the armpits; the skull of this specimen is now in the cabinet of the Boston society of natural history, and measures nearly 4 ft. from the nose to the end of the lower jaw; the head and soft parts attached weighed over 400 lbs. It is found in most of the rivers and lakes of eastern Asia and the Indian archipelago.
III. The lozenged crocodile (C. rhombifer, Cuv.) of the West Indies has the forehead surmounted by two ridges diverging backward, the upper jaw much arched transversely, the jaws narrow, the body thick, the toes and swimming membranes short, the scales of the flanks, .sides, and upper part of the neck tuberculated, and the limbs without serrated crests; the sides of the upper jaw are very prominent between the 6th and 11th teeth; the teeth are 64, 34 above and 30 below, the largest being the 2d and 7th in the upper jaw, and the 4th and 10th in the lower; on the nape are 4 small shields in one row, and on the neck 6 oval ridged plates, 4 in a row and 2 behind these; dorsal scales square, in 18 transverse rows. The general color is dark brown above with zigzag lines of deep yellow, and spots of the same on the flanks and limbs; yellow and chestnut below. It attains a considerable size. IV. The long-nosed crocodile (G. acutus, Geoff.) is found in the West Indies, particularly in Hayti, and in the northern parts of South America; it has also been found on the coast of Florida. It is characterized by its lengthened muzzle, convex forehead, and the irregular disposition of the outer dorsal scales; the hind feet are strongly webbed; on the nape are 2 or 4 shields, and on the neck 6, as in the Nilotic species; the teeth 66, 36 above and 30 below, the longest being the 4th and 10th in the upper jaw, and the 4th in the lower.
The color is brown and yellow above and yellow below. It is said to grow to a length of 20 ft. The C. cataphractus (Cuv.) and C. Journei (Bory de St. Vincent) form the connecting links between the crocodile and the gavial. - Crocodilians existed in great variety in former geological epochs, and in countries further north than the present habitats of these reptiles. The most remarkable difference between the fossil and existing species is in the form of the vertebrae; the existing crocodilians have these bodies concave in front and convex behind, and the same is true of the species of the tertiary epoch; but the fossils of the older strata have the vertebral bodies flat, or biconcave, as in fishes, or else the anterior face convex and the posterior concave, just the opposite to the existing forms. Those of the tertiary epoch are generally found in fresh-water deposits, and near the mouths of supposed rivers, so that their habits were then probably the same as now; they have been found as far north as England and France, in Asia, and in the greensand of New Jersey. During the secondary period there existed crocodilians with flat or biconcave vertebrae, resembling gavials in their lengthened cranium; from their stronger armature, more numerous ribs, and the strata in which they have been found, they were probably marine.
Among the genera are teleosaurus (Geoff.), mystriosaurus (Kaup), macrospondylus (H. von Meyer), gnathosaurus (H. von Meyer), etc, found in the liassic, oolitic, and calcareous strata. Those with an anterior convexity and posterior concavity, of which the type is steneo-saurus (Geoff.), resembled the gavials, and have been found in the lias and oolite of England.
Egyptian Crocodile (Crocodilus vulgaris).
Double-crested Crocodile (Crocoiilus biporcatus).