File:Researches on the Structure, Organization, and Classification of the Fossil Reptilia. VII. Further Observations on Pareiasaurus (1892) (14802932243).jpg

Identifier: philtrans03281945 (find matches)
Title: Researches on the Structure, Organization, and Classification of the Fossil Reptilia. VII. Further Observations on Pareiasaurus
Year: 1892 (1890s)
Authors: Seeley, H.
Subjects: Proceedings of the Royal Society of London Philosophical Transactions of the Royal Society
Publisher: Royal Society of London

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. Baini, it will be shown that the vertebral articulation # G. A. Boulenger, Zool. Soc. Proc., 1890, p. 665. AND CLASSIFICATION OF THE FOSSIL BBPTILIA. 319 of the skull with the vertebra was not transversely ovate or formed only by thebasi-occipital bone; nor did it terminate in two condyles as this specimen might havesuggested, but was circular and terminated posteriorly in a conical cup. This conicalcup is probably a primitive condition of the small pit which occurs between theex-occipitals and basi-occipitals of such a reptile as Chelone, and which is seen as arelic of the notochordal condition more or less marked in the centre of the condyle inIchthyosaurus, and many other reptiles. The persistence of this unossified conditionof the occipital condyle is particularly suggestive in relation to the double condyleswhich are developed upon the basi-occipital bone in Labyrinthodontia. For if theex-occipital bones extended backward so as to contribute to the occipital condyle (as Fig. 3.
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%nat Superior aspect of the basi-occipital bone of Mastodonsaurus giganteus, showing the two condyles formedby the basi-occipital bone. The letters EO, are placed npon the surfaces which gave attachmentto the ex-occipital bones. (From a cast of the type in the Natural History Museum.) they do in numerous reptiles both existing and fossil), the Labyrinthodont articulationwould approximate nearer to the condition in Pareiasaurus. But the Labyrintho-dontia are not amphibian in this respect, since they retain the primitive mode ofunion of the vertebral column with the skull, by means of the basi-occipital boneonly, to which Ichthyosaurus offers a nearer parallel than is found in Pareiasaurus.(It is exceptional for the skull to unite with the vertebral column by thebasi-occipital bone only, but two condyles like those of Mastodonsaurus orActinodon, formed by the basi-occipital bone, are in better osteological harmonywith the structure of Reptiles, than would be two condyles formed by the 3philtrans03281945

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