Licence: Public Domain Mark
Credit: On the os pubis of Polacanthus foxii / 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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![February 1892, Yol. xlviii.] On the Os Pubis of Polacanthus Poxii. By H. G. Seeley, Esq., E.ll.S., E.G.S., Professor of Geography in King’s College, London. The evidence of the systematic position of the Wealden fossil Polacanthus has not been very precise. Mr. Hulke in 1881 re- garded the dermal armour as closely resembling that of Scelido- saurus; and the dermal spines were compared with those of Acan- thopholis, Stegosaurus, and Omosaurus, with indications of some differences of structure. It is to the Wealden Hylceosaurus that Polacanthus was most closely allied, the resemblance in their dermal spines being very close, and their tibiae are stated to be remarkably alike. These views were adopted by Prof. Marsh, who in January ]882 placed Polacanthus in the Scelidosauridae, immediately after Hylceosaurus. When the great tuberculate shield which covers the pelvic region in Polacanthus became known in 1887 by the skill of Mr. J. Lingard in fitting it together and of Mr. Bichard Hall in removing the matrix, Mr. Hulke described the pelvis,1 and found the ilia so blended with the dermal bones that their exact form was not made out.2 The remains of the os pubis are said to be too fragmentary to give the shape of that bone; but it was thought that indications were recognizable of its division into posterior and anterior parts. I was unable to recognize any indication of that bone on the shield, and the lettering on Mr. Hulke’s figure only refers to the ischium and acetabulum. Further search fortunately resulted in detecting the missing pubis as an isolated specimen, collected by Mr. Fox with the other remains, east of Barnes Chine, in the Isle of Wight, in 1865. It appears to be indicated in Mr. Lydekker's ‘Catalogue of Fossil Beptiles in the British Museum,’ Pa t I. p. 190, by the description “a dermal scute bearing a short spine.” This bone I regard as the anterior portion of the left pubis, the short spine being the proximal portion of the post-pubis ; together they prove that the pubis in Polacanthus, while showing differences, was con- structed substantially upon what may be termed “ the Iguanodont plan.” The most obvious difference is that the anterior pre-aceta- bular portion is relatively shorter than in any genus hitherto described. The thin anterior plate of the pubis, which was vertical and compressed from side to side, thickens as it extends backward to form the superior articular surface for the ilium, the margin of the acetabulum, and the small inferior articulation with the ischium, which was not sutural. From its inferior internal side is given off the so-called post- 1 Phil. Trans. Roy. Soc. vol. clxxviii. B, pis. viii., ix. 2 The outline of the ilium is shown in pi. ix. (op.cit.), except that the inner anterior border of the bone is less clearly defined in the drawing than in the specimen.](https://iiif.wellcomecollection.org/image/b22412724_0005.jp2/full/800%2C/0/default.jpg)
