On the Gomphodontia / by H.G. Seeley.

  • Seeley, H. G. (Harry Govier), 1839-1909.
Date:
1895
Catalogue details

Licence: Public Domain Mark

Credit: On the Gomphodontia / 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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    forming its floor for l-^- inch behind the front of the alveolar margin, defined by a well-marked transverse suture. Behind the pre-maxillaries, the slight median ridge which divides the palate anteriorly into two shallow concave channels dies away posteriorly; and the palatal plates of the maxillary bones form a hard palate for a length of 1-j^y inch, meeting each other in the median line, and extending back as far as the first three molar teeth (fig. 7). Behind the maxillary bones the hard palate is continued backward by the palatine bones which join the maxillary plates by a W-shaped transverse suture, and extend back for about inch. The width of the palate is narrowest at this suture, where it is -If inch between the inner alveolar- borders. Where the hard palate terminates transversely in a concave posterior truncation, its bony vault is distinctly concave from side to side. The truncation exposes the posterior nares, which are seen as two vertically ovate channels, which appear to be separated by the median vomerine ridge, which descends to meet the palatine bones. The palatine bones are prolonged backward laterally, parallel to the maxillary bones, with which they are in contact, so that they are wedged between the vomer and the alveolar plates of the maxillary bones. They, therefore, form the entire walls of the posterior nares, except for the median dividing- vomerine ridge. From the palato-nares, the two convex ridges which extend back- ward on each side of the median ridge become smaller and narrower as they pass backward beyond the median ridge, and form two small compressed rounded eminences which approximate towards each other. A distinct ossification is seen in this specimen upon the right side, which is external to the palatine bone. It is compressed from above downward, is directed downward and backward. It extends inward to the ridge, terminating in the small mammillation just described. Its external border is reflected forward, so as to present a vertical lateral truncation, more than | inch wide and about inch deep, as preserved. This would, therefore, be the transverse bone, and it is developed with exactly the same form as that element of the skull in Lizards and Crocodiles, in contrast to the Dicynodonts, in which no transverse bone, or such an ossification, is found. The distance from the termination of the hard palate to these processes is about 2 inches, and the transverse width across them, when complete, was somewhat more. Thus far the palate is 5^ inches long. There appear to be four incisor teeth in each pre-maxillary bone, but the central four, two in each pre-maxillary, were lost before fossilization. The teeth are com- pressed from front to back, so as to form sharp lateral borders. The outermost tooth on the left side shows the edge to be serrated. The external surface is slightly ridged, and the base of the crown is thickened, so that its inner side is more convex than the outer side. The transverse measurement in a straight line over the pre- maxillary teeth is l-x% inch. Each crown is -]_%■ inch high as preserved, but all are broken. The outermost left tooth, which is enamelled for half its length, appears to have been worn with use during life; this tooth is below the pre-maxillary suture. There is an external scale-like sub-narial ossification behind this suture reaching MDCCCXCV.—B. D