REPTILIA. 283 
by the comparatively short, broad skull. In Alligator, again, the fourth 
tooth of the lower jaw, or canine, is received into a cavity of the palatal 
surface of the upper jaw, where it is concealed when the mouth is shut: in 
old individuals the upper jaw is completely perforated by these large canines. 
The entire genus is confined to the New World. In Crocodilus, the first 
tooth in the lower jaw perforates the palatal process of the intermaxillary 
bone when the mouth is closed: the fourth tooth in the lower jaw is 
received into a notch cut in the edge of the upper jaw, and is visible 
externally when the mouth is closed. ‘The genus is represented in the West 
India Islands, but probably not on the continent of America: it is also found 
in both Asia and Africa. The commissure of the jaws, in both species, 
presents a sinuous or waved margin, and the teeth are of unequal size. In 
Gavialis the jaws are very straight, and greatly elongated, so as to form a 
sub-cylindrical beak. The teeth are nearly equal in size, and similar in form, 
in both jaws; and the first, as well as the fourth tooth, on each side of the 
lower jaw, passes in a groove in the margin of the upper jaw when the mouth 
is closed. The best known species, Gavialis gangeticus, or the common 
gavial, is found in the Ganges, and probably in other rivers of Asia. The best 
known species of alligator proper is A. mississippiensis, a conspicuous inhabi- 
tant of North America. On the Atlantic coast, it occurs as far north as Cape 
Fear River in North Carolina. They were formerly very abundant in Florida, 
and of great size, individuals of 20 feet in length having been met with. They 
construct a curious nest, consisting of a cone of about four feet in diameter 
and height, composed of alternate layers of eggs and mud mixed with grass. 
The males in spring make a noise resembling the bellowing of a bull. PI. 
88, fig. T, represents one of the South American alligators. The genus 
Crocodilus is illustrated by C. vulgaris (pl. 88, fig. 8), or the common croco- 
dile of the Nile. 
The Crocodilide of the present day all possess vertebrz with concavo- 
convex articulations, or the anterior face concave and the posterior convex.- In- 
stances of this same character occur in the fossil species. Others, how- 
ever, as Pleurosaurus, Teleosaurus, Macrospondylus, &c., have concave 
articulations at both extremities. In a third series the reverse of the first 
takes place; the anterior articulations being convex, the posterior concave, 
as in Streptospondylus, Cetiosaurus, &c. About T0 fossil members of the 
family are known, comparatively few of these, however, belonging to the United 
States. Many species were of enormous size, exceeding those of the present 
day, although some of the latter have been known upwards of thirty feet in 
length. 
Fam. 9. Enaliosaurii. The remaining families of Saurians are all com- 
posed of extinct species; many of them of enormous size, and of most 
remarkable organization, fitting them for the water, the air, the land. The 
enaliosaurians are the most highly aquatic of all known saurians, and 
perhaps of all reptiles. or this mode of life they were well calculated, by 
the highly unique structure of the extremities. While all other known 
reptiles never have more than five toes, nor more than five joints to each toe, 
the enaliosaurians have to each foot an indefinite number of toes, of an 
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