270 PBOF. G, B. HOWES ON THE DETELOPSIEXT OF THE [Mar. 14, 



and certain other genera, and the more regular if not diagnostic 

 ankylosis of the first two vertebras of the Uving Pipa, Xenopus, 

 Pelobates\ and others, and of the extinct Palceobatrachus \ 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 atlaa of Sana and Siredon. 



Fig. 3. The so-called atlas of i?araa»!acro(^on, exceptional. Fig. 4. The so-called 

 atlas of Eana esctdenta : a, normal ; b, exceptional. Fig. 5. The same in 

 Eana cateshiana : 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, nerye-aperture for exit of trans-atlantal nerve ; tr, transverse pro- 

 cess ; 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 may be associated modi- 

 fications. 



In the majority of Anuran skeletons that I have examined, in 

 which co-ossification of adjacent vertebrae had been efi'ected, all 

 traces of their original lines of demarcation were lost on the ventral 

 surface, the centra passing insensibly into oiae 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 (.r) 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 Ordniing. d. Thier-Eeichs, " Amphi- 

 bien," (Bd. vi.) p. 57. 



* Cf. Walterstorff, op. cit., and Adolphi, loc. cit. p. 362. I have observed 

 a similar fusion of the first two vertebrae in individuals of Rana guppyi and 

 R, catesbiana. 



