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 Avhen the mouth is shut : iu 

 old individuals the upper jaAV is completely perfoi-ated by these large canines. 

 The entire genus is confined to the Ne^v World. In Crocodiliis, 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 

 Gavialls 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 Avhen the mouth 

 is closed. The best known species, Gavialls 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. mississippie?isis, 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, ßg. 7, represents one of the South American alligators. The genus 

 Crocodilus is illustrated by C. vulgaris ( pi. 88, ßg. 8), or the common croco- 

 dile of the Nile. 



The Crocodilida. of the present day all possess vertebrae with concavo- 

 convex articulations, or the anterior fiice concave and the posterior convex. In- 

 stances of this same character occur in the fossil species. Others, how- 

 ever, as Pleurosauriis, Teleosaiiriis, Macrospondylus, öcc, 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. <fcc. About 70 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. For 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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