son with a vertebra from the anterior dorsal region of the specimen in the British Museum, I can find absolutely no difference, except that the vertebra in Mr. Fox's specimen is a shade smaller. The centra of the anterior dorsals in the former are rather less than 0⋅7 inch long; in the latter the measurement is 0⋅63 inch. The difference, therefore, is not more than 120 of an inch. The vertebral column of the specimen in the British Museum has been particularly described by Professor Owen; but the caudal vertebræ have been much more completely cleared of the matrix since his memoir was written. The remains of eighteen vertebræ may be made out, in consecutive series, from the cervical to the posterior dorsal region; and the position of the ilium is such, that there can hardly have been more than two or three vertebræ between the hindermost of those which are visible and the sacrum. In the most anterior of these eighteen vertebræ (which may thus, probably, be the twentieth, or twenty-first., from the sacrum) the anterior, escutcheon-shaped, face of the centrum is distinctly convex from side to side, and slightly concave from above downwards, while the posterior face is markedly concave. The neuro-central suture passes through the capitular process; and the tubercular process springs much higher up upon the arch, beneath the præzygapophysis, the articular face of which looks as much inwards as upwards[1]. It is only the hindermost, or ninth, cervical vertebra of a crocodile which presents these characters. In all the more anterior cervicals the neuro-central suture passes above the process for the capitulum of the rib; I therefore conclude that, in all probability, the anterior vertebra of the Hypsilophodon skeleton belonged to the posterior region of the neck. I should think it very possible that there may have been seven, or eight, cervical vertebræ between the most anterior of those preserved and the head. In this case, the light head, borne upon the relatively long neck, will have given the fore quarters of Hypsilophodon much resemblance to those of a Monitor.
Professor Owen concludes, from certain striæ on the articular surfaces of the vertebral centra, that "the vertebral bodies of the Iguanodon were coarticulated by means of an intervertebral ligament, as in the class Mammalia;" and he emphasizes this conclusion by putting it in italics. I have little doubt that the vertebral centra of Hypsilophodon were so connected; but so are those of a Crocodile, and the fact does not constitute the slightest evidence in favour of the mammalian affinities of the Dinosauria.
In resuming my study of the specimen of Hypsilophodon in the British Museum, for the purposes of the present paper, the difficulty which had previously presented itself of reconciling what could be seen of the structure of the bones numbered 66 and 67 (tab. i. 'Fossil Reptilia of the Wealden Formation') with what is known of the tibia and fibula of the Dinosauria returned very strongly
- ↑ The two following vertebræ have similar characters; but the articular surface of the sixth appears to be slightly concave in front as well as behind. In this vertebra the transverse process springs from the arch, far above the neuro-central suture.
