Page:The American Cyclopædia (1879) Volume V.djvu/500

496 CROCODILE 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 foetal mammalia. Meyer compares the left aorta to the ductus arteriosus, and he believes this structure to be a temporary con- dition, 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 hi- bernation. 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 60 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 struc- ture 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 be- low 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 habi- tat, and of uncertain characters. The follow- ing species will sufficiently characterize the genus: I. The common crocodile of the Nile (crocodilu* 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 men- tions the spur-winged plover (vanellus), which Egyptian Crocodile (Crocodilus vulgaris). 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 quadran- gular 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 llth 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, ob- lique black bands on each flank ; beneath green- ish yellow; claws brown. It grows to the length of 20 to 25 ft., and possibly longer. A variety of this ((7. 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 (0. marginatus, Geoif.), 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 radia- ting manner. This variety grows to a large size, and is doubtless the one so often seen by Livingstone and Gumming 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 par- tially 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 undis- turbed; 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