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Show 478 DR. W. B. BE^HAM ON AN ABNORMAL [June 5, a well-marked notch (x, fig. 6) between it and the facet for the occipital condyle. The dorsal limit of the neural arch of the " atlas " is fairly distinct, except on the right side ; elsewhere the hinder margin overlaps the anterior margin of the second vertebra in the usual way, but synostosis of the zygapophyses and arches has taken place : there is no hole between them. The centra, too, are entirely anchylosed, but the line of fusion is very distinct, and, as Howes has noted \ is marked out by a prominence or ridge. This line of fusion is not symmetrical, as the drawing showTs. The secoud vertebral piece (B) (figs. 7-11) possesses three neural spines (a, b, c), but is composed of only two vertebrae on the right side, each with a transverse process (III.', IV.') ; whilst on the left there are distinctly three vertebrae represented by three transverse processes (HL, IV., V.). If this compound piece be viewed from below (fig. 8), certain faint lines are seen crossing the compound centrum in oblique directions: they are not by any means distinct, and result rather from differences in structure than from any ridge; but they indicate the planes of fusion and suggest that this piece consists of the normal 3rd vertebra (III.), followed by a semi-vertebra (IV.) on the left side, and this again by a complete vertebra (IV.', V.). This suggestion seems to receive a certain amount of confirmation from the fact that the compound centrum is curved, the concavity being towards the right. This interpretation acquires further justification from the fact that there is a half neural arch with its spine (b) separating, on the left side, the more normally constituted arches. The first of these is, however, distorted, the neural spine (a) being directed distinctly towards the left side ; the anterior zygapophyses are asymmetrical, and other evidences suggest strong compression of the arch, resulting in a forward thrusting of the left half of the arch (HI.) by the extra half vertebra (IV.). The hinder region of this compound piece is symmetrical. Here, as before, the fusion between the arches dorsally is complete, but laterally the intervertebral foramina exist-a small one on the right side (fig. 10), just admitting an ordinary needle ; two larger ones on the left (fig. 9). The transverse processes are curiously unsymmetrical (figs. 7, 8, 11). The first on the left side (III.), the strongest, is bent downwards; the third (V.) on this side is directed nearly straight outwards as in the normal Frog; whilst on the right side the first transverse process (HI.') is quite short and ends in an irregular fashion ; the second (IV.') is long, and appears to correspond in size with that of the fourth vertebra in a normal column, and, like it, is curved upwards. The corresponding transverse process of the left side (IV.) is smaller and irregular ; whilst that marked V. is directed upward and agrees with that carried by a normal fifth vertebra. 1 Howes, "Notes on the Variation and Development of the Vertebral and Limb-skeleton of the Amphibia," Proc. Zool. Soc. 1893, p. 268. |
