File:Image from page 167 of "Water reptiles of the past and present" (1914) (14773054745).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: ital; eo, exoccipital; pf, ^ other swimming animalspostfrontal; st, stapes; pt, pterygoid; q, . . , ,,. quadrate. having a powerful propelling tail, were larger than thehind ones, though not very much so. The bones of the firsttwo segments, that is, the arm, forearm, and thigh and legbones, were all short and broad, resembling those of the ichthyo-saurs more than those of any other reptiles, save perhaps thethalattosaurs, discussed below. The articular surfaces of all thethe limb bones, as in other aquatic animals, were restricted in extent,indicating limited motion between the joints, though doubtlesshaving great flexibility. In the most specialized types, such asTylosaurus, the wrist and ankle bones were almost wholly carti-laginous, just as they are in the water salamanders, and in whalesand porpoises. This tendency of the ends of long bones, the wristsand ankles as well as other bones of the skeleton, to become morecartilaginous, or less well ossified, in animals purely aquatic in

Text Appearing After Image: SQUAMATA 157 habit is a marked one. So much is this the case that paleontolo-gists always suspect water habits in reptiles showing it, even thoughbut few parts of the skeleton are known. Increase in the number of bones of the digits is a more or lessconspicuous characteristic of all mosasaurs. In those forms in

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