Page:Quarterly Journal of the Geological Society of London, vol. 29.djvu/616

530 from it a fourth and smaller metatarsal. I have extricated them from the matrix, and placed them at the inner side of the pes, as the form of the metararsal plainly indicates it to have had this position. The three toes following this inner one, counted from the tibial to the fibular border of the foot, have respectively 3, 4, 5 phalanges. They answer therefore to the 2nd, 3rd, and 4th toes in the foot of existing lizards; and I assume the small displaced toe to be the 5th; in which case it wants the basal phalanx. The other basals and the intermediate phalanges are stout, moderately long, and their distal, pulley-shaped, articular surfaces are strongly marked. The unguals are large, long, straight, and sharply pointed. They have a very conspicuous marginal claw-groove. The third is the stoutest toe; and although it has one phalanx less, it is longer than the 4th, the basal 2nd, 3rd, and 4th phalanges of which are shorter than any others, in which respect they somewhat resemble those of the corresponding toe of the Iguanodon.

Comparing Hypsilophodon with what is known of Iguanodon (for its anatomy has still many voids), the following seem to me to be some of the most striking resemblances and differences. Hypsilophodon resembles the larger Dinosaur in the peculiar form of the anterior extremity of its mandible, in the general facies of its compressed sculptured teeth (longitudinally ridged and marginally serrato-lamellated), in the form of the bones of the shoulder-girdle and also in that of the haunch-bone, in the greater size of the hind limb, the greater length and stoutness of the third toe (which corresponds in the number of the phalanges to the middle toe of Iguanodon). It differs from Iguanodon in having four toes, in the absence of that extreme shortness which marks the phalanges, especially of the outer toe of Iguanodon, and in the form of the unguals, which are long, tapering, and pointed—in the tibia being longer than the femur, the reverse of which obtains in Iguanodon—in the inner femoral trochanter being nearer the proximal end of the thigh-bone, and in the want of overhang of the margins of the anterior intercondyloid groove which marks the thigh-bone of Iguanodon and of Hadrosaurus—and particularly, as regards the manus, in the straight, symmetrical, distinctly claw-grooved unguals, which are wholly unlike the shapeless depressed unguals of Iguanodon, devoid of distinct groove for attachment of claw.

Hypsilophodon resembles Scelidosaurus Harrisonii in the number of the pedal digits, and, superficially, in the facies of the compressed teeth. This last resemblance, however, is weakened by a critical examination of the specimens themselves. In both the crown is separated from the root by a cingulum, the sides of which run out on the lateral margins of the tooth; but in Scelidosaurus no ridges pass longitudinally from the cingulum to the trenchant edge of the crown, and the serration has quite a different shape.