File:Image from page 230 of "Water reptiles of the past and present" (1914) (14792961713).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: the controversy as toits homologies is notyet quite settled. Mostauthors, until recently,have believed that its peculiar shape (Fig. 113) is due to theco-ossification of the procoracoid with the scapula instead of asusual its loss or union with the true coracoid, so called. We arenow pretty sure that this is not true, since in reality there is nosuch bone as the procoracoid, the bone so called being the real ortrue coracoid; and because, inthe second place, the long anteriorprojection called the procoracoid is really only an outgrowth of thescapula itself and not a fused, separate bone. Hence the bone isproperly called the scapula-proscapula, and not the scapula pro-coracoid, as it usually has been. The coracoids are elongate andflattened and without the usual supracoracoid foramen, so gener-ally present in reptiles. The only other reptiles having a simi-lar structure of the scapula are the plesiosaurs, and it has beenbecause of this apparent resemblance that some good paleontologists

Text Appearing After Image: Fig. 113.—Toxochelys; coracoid and scapula 220 WATER REPTILES OF THE PAST AND PRESENT have thought the turtles and plesiosaurs were allied. The sacrumis composed of two vertebrae only, and the pelvis of the usualthree bones, the ilium, the ischium, and the pubis, all covered overby the shell. In every known turtle the neck is composed invariably of eightvertebrae, but they are peculiar in many respects. In the earliestknown turtles the neck vertebrae were, as would be supposed,biconcave, but they soon became very variable in all; in each neck some are biconcave, somebiconvex, some opisthocoe-lous, and some procoelous.And Dr. Hay tells us thatthe neck has increased inlength in the later forms.The skull also is verypeculiar in that it hassome very primitive char-acters and others veryaberrant. The temporalroof, as has been said, hasno holes through it, thoughit is often reduced by theemargination of theborders, whether from be-low or behind, until insome the whole temporalregion is ex

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