Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/461

 The centrum has unfortunately been broken across, and the greater part of it, including both articular faces, is missing. Only a small part of it, including the floor of the neural canal, remains, surmounted by a singularly framed superstructure, which, although much distorted by pressure, is yet sufficiently preserved to afford a good idea of its perfect form.

The bony tissue is very compact, which makes the outer surface very smooth, and even polished. It takes principally the shape of thin plates, many of which are not thicker than stout writing-paper. Where the interior of the stouter parts of the vertebra is exposed, the broken surfaces show a thin outer shell of bone enclosing an extremely coarse cancellated tissue, the spaces of which are immense, exceeding by many times those of the cancellous tissue of all the contemporary Dinosaurs yet known to us, and reminding us in some measure of those of Pterodactylian bones.

The neurapophyses (Pl. XXII. figs. 1 & 2, np), in their present mutilated state, measure about 5 inches from front to back ; but their real length was greater, for they have suffered by the compression of the back of the vertebra. How far they descended on the sides of the centrum is not determinable ; but their present height measures about 5 inches from the floor of the neural canal to the level of its crown ; and from that to the level of the root of the neural spine is nearly 1 inch more. Their anterior margin is stout, their posterior margin thinner ; and intermediately their substance is reduced to a very thin lamina, the outer surface of which is strengthened by a series of minor buttresses and arches projecting in high relief. The greater stoutness of their anterior margin has reference to the support of the large praezygapophyses.

These latter articular processes (prz) project directly forwards in front of the neural spine, and they overhang the entrance of the neural canal (nc). Their anterior inferior angle is borne by a stout buttress which springs from the front of the neurapophysis. They have two articular surfaces : — a larger upper one, of a flat, oblong, tabular form, at the level of the base of the neural spine (the crown of the arch), directed upwards and slightly inwards, for articulation with the corresponding large oblong face of the postzygapophysis ; and a smaller subtriangular articular surface directed inwards towards the middle line, forming the sides of a notch separating the two praezygapophyses (figs. 1 & 3, n). This notch is nearly 2 inches deep from front to back. Its width is .7 inch behind, and about 1.3 inch in front.

The postzygapophyses (fig. 4, psz) lie directly under the posterior pillars of the neural spine (to be presently described). Their size and shape correspond to those of the praezygapophyses ; and their direction is the reverse, viz. downwards and slightly outwards. No notch intervenes between them as between the anterior articular processes ; but their inner borders coalesce in the middle line, and from their junction a stout plate (fig. 4, w) descends vertically to the crown of the neural canal — in other words, to the summit of the neural arch. This plate measures nearly 2 inches vertically, and it is .9 inch thick.