. Comparative zoology, structural and systematic. For use in schools and colleges. Zoology. 312 COMrARATIVE ZOOLOGY. are firmly united, and furnished M'itli numerous teeth im- planted in distinct sockets. The lower jaw extends back of the cranium. The heart has four cavities, but the pul- monary artery and aorta communicate with each other, so that there is a mixtui-e of venous and arterial blood. Tliey have external eai--openings, closed by a flap of tlie skin, and eyes with movable lids; a muscular gizzard; a long, compressed tail; and four legs, with feet more or less web- bed, and having l
. Comparative zoology, structural and systematic. For use in schools and colleges. Zoology. 312 COMrARATIVE ZOOLOGY. are firmly united, and furnished M'itli numerous teeth im- planted in distinct sockets. The lower jaw extends back of the cranium. The heart has four cavities, but the pul- monary artery and aorta communicate with each other, so that there is a mixtui-e of venous and arterial blood. Tliey have external eai--openings, closed by a flap of tlie skin, and eyes with movable lids; a muscular gizzard; a long, compressed tail; and four legs, with feet more or less web- bed, and having live toes in front and four behind. The existing species are confined to tropical rivers, and are car- nivorous. The eggs are covered with a hard shell. There are three representative forms: the Gavial of the. Fig 293—AI1i„U )r ( 1 Mtbsissijjn «*' ) '~'uiit itin States Ganges, remarkable for its long snout and uniform teeth ; the Crocodile of the Nile, whose teeth are unequal, and the lower canines fit into a notch in the edge of the npper jaw, so that it is visible when the mouth is closed; and the Alligator of the Mississippi, whose canines, in shutting the mouth, are concealed in a pit in the upper jaw. The toes of the Gavials and Crocodiles are webbed to tlie tip; those of the AlHgators are not more than half-webbed. In the mediasval ages of geological history, the class of Eeptiles was far more abundantly represented than now. Among the many forms which geologists have unearthed. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Orton, James, 1830-1877. New York, Harper and brothers
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