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: nd themiddle, each mandible has a remarkable joint, quite unknown inland lizards, though a trace of it is found in the monitors, per-mitting much movement between the front and back parts, bothlaterally and vertically, though chiefly in the former direction.Furthermore, as in land snakes but not as in land lizards, thefront ends of the two sides of the jaws were somewhat looselyattached to each other by ligaments. This looseness of the twosides of the jaws, not only in front but also behind, together withthe joint in each, was of the greatest use in swallowing prey, aswill be explained farther on. As in most other aquatic reptiles, the neck was short and strong,the vertebrae being less in number than in most other lizards.The trunk was long and slender, more especially so in the surface-swimming kinds, with from twenty-two to thirty-four vertebrae. SQUAMATA 155 The tail was long, no longer than the tail of some land lizards,but more powerful, and broader and natter. It was expanded or

Text Appearing After Image: Fig. 72.—Skulls of mosasaurs. Upper figure, Clidastes, from the side; middlefigure, Platecarpus, from below; lower figure, Tylosaurus, from above: an, angular;bs, basisphenoid; c, coronoid; ep, epipterygoid; fr, frontal; j, jugal; I, lacrimal; m,maxilla; na, nasal; oc, occipital condyle; pa, parietal, palatine; pm, premaxilla;pf, prefrontal; pt, pterygoid; po, postorbital; q, quadrate; sp, splenial; sq, squa-mosal; Ir, transverse; v, vomer. dilated more or less toward the free end, that is, with the beginningof a terminal caudal fin, such as the more specialized ichthyosaursand crocodiles possessed. The vertebrae were procoelous, that is, 156 WATER REPTILES OF THE PAST AND PRESENT concave in front and convex behind, like those of most modernlizards and all modern snakes and crocodiles, but quite unlike thebiconcave vertebrae of all other aquatic reptiles. This kind ofarticulation of the backbones gave greater firmness and strengthto the spinal column, but decreased the flexibility,

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