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Show 270 PROF. G. B. HOWES ON THE DEVELOPMENT OF THE [Mar. 14, and certain other genera, and the more regular if not diagnostic ankylosis of the first two vertebrae of the living Pipa, Xenopus, Pelobates1, and others, and of the extinct Pedazobatrachus1. The fact that Ceratophrys and Pelobates, in which this tendency towards a greater fusion is well marked, are possessed of a relatively short So-called atlas of Eana and Siredon. Fig. 3. The so-called atlas of Eana macrodon, exceptional. Fig. 4. The so-called atlas of Rana esculenta : a, normal; b, exceptional. Fig. 5. The same in Eana catesbiana: a, normal; b, exceptional. Fig. 6. The same in the Mexican Axolotl, Siredon pisciformis. All from the ventral aspect. Figs. 3, 4, and 6 enlarged. n, nerve-aperture for exit of trans-atlantal nerve ; tr, transverse process; x, eminence at point of fusion of adjacent vertebral bodies. urostyle, invests the aforenamed anticipation with an amount of interest, by way of suggesting that the reduction in length of the urostyle and the vertebral ankylosis m a y be associated modifications. In the majority of Anuran skeletons that I have examined, in which co-ossification of adjacent vertebrae had been effected, all traces of their original lines of demarcation were lost on the ventral surface, the centra passing insensibly into one another. In the Frog first described this was otherwise, for its vertebral column when viewed from beneath (fig. 1 a) or from the side (fig. 1 c), revealed a couple of eminences (x) at the point of fusion of the two terminal vertebrae. There is no variation to which the Amphibian vertebral column 1 Cf. Hoffmann, in Bronn's Klassen und Ordnung. d. Thier-Eeichs, " Amphi-bien," (Bd. vi.) p. 57. 2 Cf. Walterstorff, op. cit., and Adolphi, loc. cit. p. 362. I have observed a similar fusion of the first two vertebrae in individuals of Eana guppyi and E. catesbiana. |
