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: heir mates or with contiguousbones. The crocodile has at leasttwo pairs of bones which havedisappeared in turtles. On theother hand, the turtle has at leastone pair of free bones which havebeen fused with adjacent bones inthe crocodiles, and one pair thatis fused which is free in the latter.The lizard has one pair of bonesthat has been wholly wanting inother reptiles for millions of years,while on the other hand it has lostsome bones that are present in all other modern reptiles. Thefour parts of the occipital bone of mammals, basioccipital, exoccipi-tals, and supraoccipital, are almost invariably free and there is asingle occipital condyle, except in the Theriodontia. In this reduction or fusion of parts, or in addition thereto, therehas been a general lightening-up of the whole skull-structure inreptiles from the rather massive and protected form of the olderto the lighter, less protected, and more fragile type of thelater ones, since speed, greater agility, better sense organs, and

Text Appearing After Image: Fig. 6.—Labidosaurus, a cotylosaur.Skull from above: pm, premaxilla; n,nasal; m, maxilla; /, lacrimal; p, pre-frontal; fr, frontal; pf, postfrontal;po, postorbital; j, jiigal; pa, parietal;sq, squamosal; ds, dermosupraoccipi-tal; pf, parietal foramen. THE SKELETON OF REPTILES 23 doubtless greater brain power have rendered unnecessary or uselesstrie older kinds, just as modern methods and modern arms haverendered useless the coat of mail of the Middle Ages. The old reptiles had a continuous covering or roof for the skull,pierced only by the openings for the nostrils in front—the nares—the orbits for the eyes near the middle, and a smaller median open-ing back of them for the so-called pineal eye. The temporalregion, that is, the region back of the orbits on each side, wascompletely roofed over by bone for the support and protection ofthe jaw muscles. In later reptiles this region has been lightened.

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