Further observations on Pareiasaurus / by H.G. Seeley.

  • Harry Govier Seeley
Date:
1892
Catalogue details

Licence: Public Domain Mark

Credit: Further observations on Pareiasaurus / by H.G. Seeley. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    tory chamber in Ichthyosaurus; and, behind that, what I regard as the opisthotic bone diverges outward and backward. The palate, as a whole, gives the impression of carrying four parallel rows of teeth in the middle, and three oblique rows on each side. The inner longitudinal rows number about 35 teeth; the outer longitudinal rows contain 50. There are about 20 teeth in each of the pairs of lateral oblique rows except the hindermost, in which there are a dozen. The rows of teeth are approximately in the same horizontal plane, but tlie palatine rows ascend a little as they extend outward. I am acquainted with no other South African genus of Reptile in which teeth are developed to the same extent in rows on the palate. There is an interesting though distant approximation to this condition in the palate of Procoloy)hon, which may probably be referred to a division of the same ordinal group. Teeth occur upon the palate in rows in Endothiodon, but in that genus there are no teeth on the aveolar border. It is only in Ilypcroda'pcdon that the individual teeth on the palate are anything like as numerous, or the rows as numerous. The only genera in which teeth have been recorded on the vomers, palatines, and pterygoid bones are Champsosaurus and Ophiosaurus* In Rhopalodon teeth are figured upon the pterygoid bones. The basi-sphenoid extends backward behind the palate, as an oblong mass, with concave sides and a concave median channel. Its rounded lateral ridges descend anteriorly, and expand into buttresses which support the palate on each side of the posterior nares. The specimen gives no certain evidence that the pterygoids overlap the inferior surface of the basi-sphenoid in the way which the specimen figured (‘ Phil. Trans.,’ 1888, B, Plate 15) appeared to indicate, though the bone is fractured in an almost identical way. The posterior transverse sutures on the basi-sphenoid are evident, but curve forward in the middle line, instead of backward, and indicate the close structural union between the basi-sphenoid and basi-occipital bones. There is au indication of the presphenoid imperfectly j)reserved. The basi-occipital region has the infeiior part of the condyle prominent and defined inferiorly by a groove which separates an infero-lateral process on each side. Its inferior margin is partly obscured by a large intercentral bone (Plate 20, to), similar to that figured' Phil. Trans.,’ 1888, Plate 20, behind the interclavicle, and it was probably the close union of this element with the basi-occipital which suggested my interpretation of the imperfectly preserved condyle as rounded inferiorly, loc. cit., p. 70. The ex- occipital bones are not preserved, but there is a transverse suture imj)erfectly exposed which shows the position they occupied ; and the posterior articular aspect of the basi-occipital is a large V'shaped concavity. This concavity defines two lateral areas, which extend backward 2’5 centims. beyond the transverse line, on the superior surface. The margin of this articular border is obscured by its close union on the right side with the displaced wedge bone. From other evidence, subsequently referred to in the skull of P. Baini, it will be shown that the vertebral articulation * G. A. Boulengee, ‘ Zool. Soc. Proc.,’ 1890, p. G65.
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