473 DR. W. B. BENHAM ON AN ABNORMAL [June O,^ 



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 anehylosed, but the line of fusion is 

 very distinct, and, as Howes has noted ', is marked out by a pro- 

 minence or ridge. This line of fusion is not symmetrical, as the 

 drawing shows. 



The second vertebral piece (B) (figs. 7-11) possesses three neural 

 spiues (n, b, c), but is composed of only two vertebrae on the right 

 side, each with a transverse process (11 [.', IV.') ; whilst on the left 

 there are distinctly three vertebra? represented by three transverse 

 processes (III., IV., A 7 .). 



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 rat her 

 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 (HI.), 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 furl her justifica- 

 tion from the fact that there is a half neural arch with its spine (/>) 

 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 (III.) 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 til' (he 

 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, u Notes on the Variation and Development of the Vertebra] and 

 Limb-skeleton of the Amphibia," I'roc. Zool. Soc. 1893, p. 268. 



