File:Image from page 98 of "Water reptiles of the past and present" (1914) (14769833011).jpg

Identifier: waterreptilesofp1914will Title: Water reptiles of the past and present Year: 1914 (1910s) Authors: Williston, Samuel Wendell, 1851-1918 Subjects: Aquatic reptiles Publisher: Chicago, Ill., The University of Chicago Press Contributing Library: Boston Public Library Digitizing Sponsor: Boston Public Library

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Text Appearing Before Image: maxilla; m, maxilla; po, post-structure of its paddles some- orbital; j, jugal.what intermediate between that of the earlier Plesiosaurus and the later Trinacromerum.The skull of the long-necked plesiosaurs is surprisingly smallin comparison with the remainder of the skeleton, often verysnake-like in shape, though very un-snake-like in structure. Theshort-necked plesiosaurs had often a relatively larger skull, mPlio-saurus, for instance, more than five feet long, sometimes ratherbroad and short, sometimes remarkably long and slender. Theexternal nostrils were situated far back, very near the eyes, andwere very small. The eyes, of considerable size, though by nomeans so large as those of the ichthyosaurs, were directed laterally,and were provided with a ring of bony sclerotic plates—rathersmall and weak ones, however. The quadrate bones—bones pecu-liar to the reptiles and birds—to which the lower jaws are articu-lated, are, as in the ichthyosaurs and crocodiles, rigidly fixed and

Text Appearing After Image: 88 WATER REPTILES OF THE PAST AND PRESENT immovable. The lower jaws, always rather slender, are firmlyunited in front, sometimes for a long distance, as in the moderngavials. The teeth of the broad-headed plesiosaurs are long,slender, pointed, and recurved, of a murderously cruel shape; theyare deeply implanted in sockets, and number from twenty tothirty on -each jaw above and below. There are no teeth on thebones of the palate, such as the mosasaurs possessed. The slender-jawed, gavial-like plesiosaurs have more numerous, but smallerteeth. The surface of the skull on each side behind, for the attach-ment of the muscles closing the mandibles, is of great extent; insome this surface is increased by a high, thin crest in the middle,as in strongly carnivorous animals, all of which give conclusiveevidence of the powerful muscles used in biting and seizing. Thereis but one temporal opening on each side, as in the ichthyosaurs

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