OCR Text |
Show 236 DR. A. S. WOODWARD ON THE [Apr. 18, the side. The neural canal in transverse section is somewhat deeper than broad. The neural spines are laterally compressed, thinnest at their front rugose border, and hollowed at the apex ; they bear no lateral ridges, but their postero-lateral edges are produced into a pair of laminEe, which gradually expand downwards into the posterior zygapophyses. The next caudal vertebra in the same specimen is probably the fourth, and is comparatively well preserved with its neural spine complete (text-fig. 41, p. 235). The centrum is concave in front, but flattened or even slightly convex behind ; and it is much constricted between the prominent rims of its two faces, without any trace of lateral pits. It is slightly broader than deep, and the transverse processes (incomplete in the fossil) arise within the upper half. Each lower border is impressed by a facette for the chevron-bone, the hinder being larger than the anterior impression. The neural arch is very massive, and the neural canal is still somewhat deeper than wide. The bases of the anterior zygapophyses (az.) prove them to have been very stout; and a thin vertical lamina or lateral flange of bone extends downwards from the level of these zygapophyses to the transverse processes on the centrum. The neural spine is massive and placed above the hinder half of the centrum, slightly curved backwards but scarcely overlapping the next vertebra; it is laterally compressed, thinnest at its front rugose border, and somewhat hollowed and roughened at its truncated upper end. There is a slight oblique ridge extending upwards and backwards from the anterior zygapophysis on each side but soon disappearing ; and the posterior lateral edges of the spine are produced into rather stout laminae which would originally terminate below in the posterior zygapophyses. These zygapophyses evidently converged below into a short median ridge or zygosphene, which fitted into the zygantrum between the anterior zygapophyses of the succeeding vertebra. In this next vertebra part of the bony lamina above the transverse process on the left side is well preserved, while the oblique ridge above the anterior zygapophysis is comparatively strong. The four associated anterior caudal vertebrae of another specimen (Brit. Mus. no. 11. 1984) are also very short and broad, with deeply concave anterior face and nearly flat posterior face. The largest closely resembles the anterior caudals just described, and exhibits part of the lateral flange of bone which extends upwards from the transverse process to the level of the zygapophyses. The others are evidently intermediate between the most anterior and the middle caudals, and one of them is represented in text-fig. 42, p. 237. This specimen shows the complete length of the transverse processes. It has a less elevated neural arch than the vertebra? already described, and exhibits the lateral bony flange above the transverse process reduced to a slight rounded ridge. Apart from the specimens just mentioned, the few vertebra intermediate between the most anterior caudals and the middle caudals are unknown; but the latter are represented by a fine |