Note on the pelvis of Ornithopsis / by H.G. Seeley.

  • Harry Govier Seeley
Date:
1889
Catalogue details

Licence: Public Domain Mark

Credit: Note on the pelvis of Ornithopsis / 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.

    5/10 page 393
    Mr. ITulke does not expressly determine these pelvic bones as right or left, and he is equally indefinite with regard to the remains of the Wealden Ornithopsis. Still the fact that Professor Marsh figured the external surface of the pelvis of Atlantosaurus, and that Mr. Hulke has copied that figure reversed in pi. xiv. Quart. Journ. Geol. Soc. vol. xxxviii. in illustration of what I regard as Ornithopsis Hullcei, is some evidence that the figured surface was regarded as external, and the bones as belonging to the right side of the skeleton *. However this may he, I had no doubt that the figured surface in Ornithopsis Leedsii is the internal or visceral surface, and therefore the bones are of the left side; and the Wealden specimen shows substantially the same characters. This difference in inter- pretation involves a totally different conception of the nature of the pelvis, and supposing the ilium to have been correctly determined, its chief extension may he varied, as I traced the sutural surface on the pubic bone which extends in the median line of the body of the animal. Mr. Alfred N. Leeds had the kindness to remove these massive specimens from their positions in his museum, so that the bones from the right and left sides of the body might he adapted to each other in the inclined positions which I regarded them as having occupied during the life of the animal. It then became manifest that the bones were united in the median line almost throughout their length by a median suture, and that they formed a saddle- shaped surface from front to hack, as do the larger Plesiosaurs from the Oxford Clay. The left pubis becomes thickened at its anterior extremity, which shows a cartilaginous surface; hut internally there is a well- marked suture in the median line, which is bevelled at an angle of 45°. This articulation is six centimetres deep and about 24 centim. long, terminating posteriorly in a sharp point, where there is a small median foramen between the bones, with a well-ossified border. This suture ascends in level as it extends backwards. The internal surface of the pubis is flattened, and the external surface is convex transversely over this anterior portion of the bone. Behind this suture the bone is bent in an arch, so that its external surface is con- cave from front to back along the median line. On the inner margin the median sutural surface is prolonged for 25 centim., behind which the continuity of the bones is interrupted by a smooth border to a notch which may have separated the bones by 14 or 15 centim. In the middle, where it is strongest, this posterior part of the sym- physis is 4 centim. in vertical depth. It is inclined to the internal surface, but to a less degree than the anterior part of the symphysis, consequent on the arched form bringing the hinder part of the pubic symphysis into a superior position, so that the bones of the two sides meet at a less acute angle. The two pubic bones are thus so inclined to each other as to enclose an anterior basin and a posterior basin, which are separated by the intervening saddle-shaped arch. * Mr. Lydekker adopts this determination in the British Museum Catalogue, vol. i. p. 150, describing the bones as associated right ischium and pubis.
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