On the anomodont Reptilia and their allies / by H.G. Seeley.

  • Seeley, H. G. (Harry Govier), 1839-1909.
Date:
1889
Catalogue details

Licence: Public Domain Mark

Credit: On the anomodont Reptilia and their allies / 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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    height there is no indication of its existence in the figure; but in the specimen the bone projects forward a little, and is well defined by a groove above it. Its inner border is convex, and the pterygoid unites with that border, just above the condyle, by an attachment which is 2 centims. deep. The attachment was not firm, for dn D.pardiceps and other species the quadrate bones are lost from the otherwise perfect skull. The Dicynodon pardiceps (Owen), South African Cat., No. 70 ; Brit. Mus., No. 47,045, in many respects the most instructive of all the specimens, has never- been adequately described. It shows details of structure, owing to the softness of the matrix, which manifest the union between many of the bones. The remarkably elongated zygomatic arch I find formed chiefly by the squamosal bone, which extends forward to the orbit. The maxillary bone also contributes to form it. extending below and behind the squamosal backward, almost to the descending process. The malar bone forms the lower border of the orbit. It rests externally upon the squamosal, and internally upon the maxillary; its posterior extremity supports the post-frontal bone, and its anterior extremity appears to extend forward to the lachrymal, and inward to meet what I take to be an outwardly directed process of the palatine. The post-frontal is a slender transverse bar, and meets the frontal by a well defined suture. The small parietal lies in front of the parietal foramen; but I do not feel certain that the long oblique posterior processes are rightly referred to that bone, and it would seem as though the analogous structure in Lizards had suggested an explanation which has not been questioned. These bones seem to me to diverge anteriorly to expose the parietal, and they diverge posteriorly to support the squamosals. If they are separate ossifications, they may represent external elements in the Amphibian skull which have remained after a deeper seated ossification was developed, j ust as in some types basi-temporals remain after the sphenoid is ossified. In Dicynodon pardiceps a groove connects the upper posterior corner of the nasal aperture with the orbit, much as in Pareiasaurus, though the depression is but slightly marked. In D. leoniceps the region behind the nares is impressed over the depth of the apertures. In Dicynodon tigriceps (Owen) the configuration of the zygoma and temporal fossa is stated to be most nearly paralleled in Chelydra, though the difference is considerable. In another specimen referred to the same species, the inter-orbital space is said to be more completely ossified than in modern Crocodilia, Chelonia, or Lacertilia, and is an approximation to Mammalian structure. The upper anterior angle of the pterygoid is said to join the anterior extension of a cranial bone which may correspond with the pre-sphenoid of Crocodiles, or the orbito-sphenoid of Chelonians. The reference of this specimen to D. tigriceps is on several grounds open to question. But the bone which the author regards as pre-sphenoid (5) seems to me to be the median plate of the pterygoid. It is possible that a small ossifica- tion above this, which extends obliquely forward and upward, may be the pre- sphenoid, for it is in the position which the pre-sphenoid should occupy. The bone