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Show 268 PROF. G. B. HOWES ON THE DEVELOPMENT OF THE [Mar. 14, 5. Notes on Variation and Development of the Vertebral and Limb-Skeleton of the Amphibia. ByGr. B. HOWES, F.L.S., F.Z.S., Assistant-Professor of Zoology, R. Coll. Sci. Lond. [Eeceived March 14, 1893.] Vertebral Column.-Numerical variation of the vertebrae 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 1, 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 vertebras 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 (Bufo var.) specially examined2, 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. Rare as the fusion of the terminal vertebras of the living Anura would thus appear to be, it is a remarkable circumstance that Walterstorff, w;ho has shown 3 the Tertiary genus Palceobatrachus 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, lb) a second sacral transverse process should appear on one or both sides. Such, however, was not the case; for the transverse processes 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 Adolphi4, the Palaeobatrachoid condition was much more nearly realized, as the fusion had involved the transverse processes of the 8th and 9th 1 Morpholg. Jahrb. Bd. xix. pp. 331-375. As this author's list of references is incomplete, the contributions of Sasserno and others having been apparently overlooked, I a m compelled to refer the reader to an earlier paper of m y own (Journ. Anat. & Phys. vol. 24. p. xvi app.) for a full record up to the time of writing. 2 Loc. cit. p. 351. 3 Jahrb. naturwiss. Vereins, Magdeburg, 1885-86. 4 Loc. cit. p. 366, pi. xii. fig. 4. |
