268 PBOF. G. B. HOWES ON TKE DETELOPMENT OE THE [Mar. 14, 



5. Notes on Variation and Development of the Vertebral 



and Limb- Skeleton of the Amphibia. By G. B. Howes, 



F.L.S., F.Z.S., Assistant-Professor of Zoology, R. Coll. 



Sci. Lond. 



[Receiyed March 14, 1893.] 



Vertebral Column. — Numerical variation of the vertebra of 



Amphibia has been from time to time recorded by various authors, 



and in dealing with the living Anura, Adolphi, as the result of a 



recent extensive enquiry \ has been enabled to classify the types 



of variation met with into three orders, as chiefly determined by 



the fusion of adjacent vertebrae throughout this or that definitely 



restricted region. There has recently come into my possession 



the skeleton of an edible Frog {Rana esculenta) in which (fig. 1 a) 



the eighth and ninth vertebrae were immovably united; and 



although this union is in itself an apparently trivial matter, the fact 



that Adolphi found but one such case in 212 individuals of the 



Toad (Biifo var.) specially examined -, is sufficient testimony to the 



rareness of the occurrence to warrant its being placed on record. 



So far as I am aware, Adolphi's example and those herein recorded 



are the only ones in which this particular fusion has been yet 



described, the majority of recorded variations having chiefly 



involved the head of the urostyle and sacrum. Eare as the 



fusion of the terminal vertebrae of the living Anura would thus 



appear to be, it is a remarkable circumstance that Walterstorff, 



who has shown ^ the Tertiary genus Palaohatraclius to be possessed 



of a compound sacrum of usually three vertebrae, regards the 



fusion of these as normal and characteristic of the genus. 



On general morphological grounds there is good reason, as need 

 hardly be pointed out, for associating the compound sacrum and 

 the fusion of the sacral vertebrae together ; and it might therefore 

 reasonably be expected that in the Frog herein described (figs. 1 a, 

 1 6) a second sacral transverse process should appear on one or both 

 sides. Such, however, was not the case ; for the transverse pro- 

 cesses of the last two vertebrae were in no way exceptional either 

 in disposition or relationship. This is the more remarkable, as 

 the 8th vertebra of this animal is known to occasionally enter into 

 the composition of the sacrum on one or both sides, while still 

 free and independent. In the Toad described by Adolphi \ the 

 PalcTobatrachoid condition was much more nearly realized, as the 

 fusion had involved the transverse processes of the 8th and 9th 



1 Morpbolg. Jabrb. Bd. xix. pp. 331-375. As this author's list of refer- 

 ences is incomplete, the contributions of Sasserno and others having been 

 apparently overlooked, I am compelled to refer the reader to an earlier paper 

 of my own (.Tourn. Anat. & Phys. vol. 24. p. xvi app.) for a lull record up to 

 the time of writing. 



^ Loc. cit. p. 351. 



3 Jahrb. naturwiss. Vereins, Magdeburg, 1885-86. 



* Loc. cit. p. 366, pi. xii. fig. 4. 



