Page:Quarterly Journal of the Geological Society of London, vol. 29.djvu/612

526 The general form and the facies of the cylindrical teeth of Hypsilophodon are so like those hitherto generally regarded as Hylæo- saurian that I cannot help suspecting that these reputed Hylæosaurian teeth may really be the as yet unknown premaxillaries of Mantell's Iguanodon; and the suspicion derives strength from the fact that these teeth are not very rare in those Isle-of-Wight Wealden beds which also yield Iguanodon remains, whilst other indisputable remains of Hylæosaurians are extremely infrequent anywhere in the island Wealden formation.

Vertebral Column.—All the vertebræ were crushed and mutilated beyond reparation. A few centra which I recovered show that both articular surfaces are nearly plane; or else the periphery is plane or gently swollen, and the middle is very slightly hollowed. The outer or non-articular surface is smooth. The sides are scarcely convex vertically, and slightly concave horizontally. In all the vertebræ the neurapophysial suture persists, as Prof. Owen found in the Mantell-Bowerbank skeleton; and the neurapophysis had, in most instances, separated from the centrum. The neural canal, in the neck-vertebræ, is very capacious; and the spinous processes are dwarfed here. The neural surface of the centrum has a narrow longitudinal median groove not covered by the neurapophyses, a fact mentioned by Prof. Owen. In some centra this groove has the form of a deep cleft, which sinks below the level of the middle of the centrum.

Two centra from, I think, a little in advance of the sacrum are respectively ⋅7 and ⋅65 inch long, and ⋅4 inch in their vertical diameter. A mutilated sacrum of an older individual consisted of four anchylosed centra, with a small remnant of a fifth.

Ribs.—Associated with the vertebral column of the base of the neck and front of the chest were many fragments of double-headed ribs.

Shoulder-girdle and fore limb.—The scapula, coracoid, and left humerus I found lying close together; and near these, in other blocks of clay (for the cliff was very fissured), was a forearm with its manus, and a flat bone, presumably the sternum.

The scapula (fig. 2, a) is a long thin slightly recurved blade, a little expanded at the vertebral end, and widening considerably towards its articular extremity. Its anterior margin, in the middle two thirds, is nearly straight; towards the ventral end it bends forwards and includes an acute angle with the coracoid border, whilst dorsally it curves backwards. The expansion of its dorsal and ventral ends renders the posterior border concave. The articular border is divided into two facets, of which one is longer, straight, anterior, for union with the coracoid; and the other, shorter, stouter, and posterior, forms half of the glenoid fossa (fig. 2, b). These two facets, in my specimen, include an angle of about 125°. A larger scapula, of a probably mature individual, had a longer and narrower blade, and what seemed to me a short precoracoid process.

Compared with the scapulas of other Dinosauria, that of Hypsilophodon (particularly when fully grown) resembles that of Iguanodon Mantelli in the length and narrowness of the blade, and, unless appearances have misled me, in the presence of the precoracoid