Page:Quarterly Journal of the Geological Society of London, vol. 29.djvu/609

1873.] centrum in the same block of stone with the skull further enabled Mr. Huxley to identify Hypsilophodon with the Mantell-Bowerbank skeleton.

In the discussion which followed the reading of this paper I alluded to part of a reptilian skeleton from the same cleavage-bed, shown me by Mr. Fox in 1869, which I considered to belong to Hypsilophodon. It consisted of a connected chain of several pre- and postsacral vertebræ, the right ilium with the proximal end of the femur in the acetabulum, and the distal half of the leg with the tarso-metatarsus. The ilium was prolonged forward for a considerable distance in front of the acetabulum. The knee-joint had been worn away; but its position in the block, ascertained by prolonging the directions of the remaining parts of the tibia and femur, made it very probable that the leg was longer than the thigh.

The above are all the published notices of the anatomy of Hypsilophodon Foxii with which I am acquainted.

In several visits to the Isle of Wight I have obtained additional evidence of its structure; and having quite recently been so fortunate as to exhume from the same Cowleaze bed great part of a skeleton of this reptile, I am now able to communicate many details respecting its dentition, and also the form of the mandibular symphysis, not illustrated by Mr. Fox's skull, as well as the forms and proportions of several bones of the shoulder and hip-girdles, and fore and hind limbs, before unknown.

Probably the entire skeleton was present; but its immaturity and the fissured state of the clay in which it was lying were so unfavourable to the preservation of the bones, that most of them were too much shattered to bear removal, and of many I could only bring away ideas, the bones themselves falling into numberless small pieces, which no pains or ingenuity could join.

Skull.—The only remnants of this which I could save were parts of the jaws and of one orbit. In the clay filling the orbit were several small osseous scales, which I judged to be vestiges of a sclerotic ring; and deeper than these was a large and extremely thin bony lamina, apparently an extensively, if not, indeed, completely, ossified interorbital septum.

The largest piece of jaw is the right mandibular ramus (Pl. XVIII. fig. 1). The outer surface and dentary border are laid bare. Its length from the front of the symphysis to the front of the quadratic joint (behind which the bone is defective) is 2⋅5 inches. The upper border slants from the quadratic joint steeply upwards to the coronoid process, the top of which is wanting; and from here it declines gently forwards through a space of 1⋅6 inch, which comprises the entire tooth-bearing portion. In front of this, at the distance of ⋅35 inch from the symphysis, it abruptly falls; and the surfaces, which behind this point look inwards and outwards, acquiring an upward and downward aspect, one half of an edentulous mental interdentary groove (fig. 1, a) repeats in miniature the characteristic depressed symphysis of iguanodon. In front of this extremity of the mandible, and quite distinct from it, is a thin triangular plate, which I suspect