On Pareiasaurus bombidens (Owen), and the significance of its affinities to amphibians, reptiles, and mammals / by H.G. Seeley.

  • Seeley, H. G. (Harry Govier), 1839-1909.
Date:
1888
Catalogue details

Licence: Public Domain Mark

Credit: On Pareiasaurus bombidens (Owen), and the significance of its affinities to amphibians, reptiles, and mammals / 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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    the posterior origin of the supra-narial canal, which appears to expand towards the orbit, just as it expands towards the narine. There is no recognisable lachrymal perforation, and the lachrymal bone is either absent, or represented by a scale in the mucus-canal which appears to be perforated. The bones which form the superior border of the orbit are very thick, but the maxillary bone below is comparatively thin. The measurement from the upper border of the orbit to the median line of the skull is 10 centims., and the transverse measurement over the skull at the lower orbital border would be about 28 centims. These are apparently the only vacuities in the skull, though minute temporal fossse, like those seen in Capitosaurus, may exist in the posterior region in the area of the squamosal bone, which is badly preserved; but the evidence on this point is very unsatisfactory. The Premaxillary and Sub-narial Bones. (Plate 14, fig. 1, pm. in.) The premaxillary bones are separated from each other by a median suture. They are narrow, and rise above the lower nasal border in an inter-narial process, which is fractured. There is no evidence which is quite conclusive as to the form and size of the bone. In the type-specimen of P. bombidens (British Museum Register, 43,525) 1 am clear that each bone only contains two teeth. But besides the suture, which extends obliquely outward, upward, and backward, giving an apparent superior width of 7‘5 centims. to the bone, there is also a suture which ascends over the second tooth inward to the lateral margin of the ascending premaxillary process. These two sutures define a triangular plate, the apex of which descends between the second and third teeth, and the base of which extends along the narine. I regard this bone as a dermal plate, which hides the suture between the premaxillary and maxillary bones. It may be termed sub-narial, aud is- regarded as belonging to the same series as the supra-orbital, infra-orbital, and lachrymal bones of other animals. Professor W. K. Parker, F.R.S., has described skeletal elements above the maxillary and below the nasal, forming a floor to the nostril, as characterising Urodeles and Anurous Batrachia, Varanian and other Lizards, and Snakes,* with which this ossification may, I think, be compared. In the specimen of Pareiasaurus now described, the structure of this region of the jaw is less clear, because the sub-nasal scale is so perfectly blended with the bones beneath, that its sutural limits are not very distinct. Hence the premaxillaries are narrow bones, formed on the Amphibian rather than a Mammalian type, which become narrower as they extend superiorly towards the nares. Their external surface is flattened, and retreats a little as it ascends, in harmony with the convex rounding of the snout. The fractured superior surface of the premaxillaries is oblong, having an antero-posterior extension * ‘ Phil. Trans.,’ 1878, p. 412.