Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/95

1869.] to my mind. On the other hand, my present knowledge of the strange characters of the pelvis in the Dinosaurian reptiles led me to suspect that those bones might prove to be the pubis and ischium in situ, and in their natural connexion with the right ilium, the posterior part of which bone (numbered 62 in the plate cited) was conspicuously visible. Careful search revealed the anterior end of the bone overlying the arch of the posterior vertebræ of the dorsal series.

With the permission of the Keeper of the fossil collection, therefore, the specimen was subjected to a further careful removal of the matrix in the requisite directions. The result has been the complete verification of my conjecture, and the specimen now affords a view of the ventral elements of the pelvis in their natural relations (Pl. II.).

The middle part of the right ilium is covered, and, seemingly, a little crushed in, by the left foot. But its broad postacetabular portion (b), and its relatively narrow and pointed præacetabular part (a) are completely exposed. I suspect that the ilium is broken in the middle, and, as a consequence, that the distance from the posterior to the anterior ends of the visible parts of the bone (6⋅6 inch) is somewhat greater than it should be. Hence the acetabulum probably appears to be longer than it naturally is. The postacetabular process (c), which should articulate with the ischium, is swollen and thick, but thins off, above and behind, into a thin vertical plate, the posterior curved margin of which is broad and turned in, like a narrow shelf. The præacetabular prolongation is slender, and its broken narrow end (a) rests on the arch of the seventeenth vertebra.

The anterior boundary of the acetabulum is formed by a broad, somewhat flattened, facet of bone (d), which looks backwards and a little outwards. The osseous mass, of which this forms the posterior aspect, rapidly narrows forwards, and is prolonged above into a slender ridge, or process, with a free rounded end (a). In front, it has a sinuated free edge; anteriorly and below, it is continued into a slender rod-like pubis (Pb), between six and seven inches long, which passes downwards and backwards parallel with the ischium. On the outer surface, in front of the lower part of the articular surface, lies an oval foramen (e). The posterior edge of the bone is concave and free. Posteriorly and below, it ends in a broad thin prolongation, which passes backwards, internal to the ischium. The part of the bone which bears the facet answers very well to the præacetabular process of the ilium of Megalosaurus and of Thecodontosaurus. The perforation is indeed somewhat like that which is so generally found in the pubis of Lizards; but, on a future occasion, I hope to be able to show its analogue in the ilium of an undoubted Dinosaurian. If this part of the acetabular wall answers, as I believe it does, to the descending præacetabular process of the ilium, all trace of the suture between it and the pubis has disappeared.

The right ischium (Is) lies in undisturbed relation with the pubis. Its acetabular end has a free superior concave edge which bounds the acetabulum below, a broad thin anterior process which