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Show 1893.] VERTEBRAL AND LIMB-SKELETON OF THE AMPHIBIA. 275 has long ago worked out * its fundamental relationships during development to the remaining osseous elements entering into the composition of the adult urostyle. v.aX. 71 c v.ee.TK ceJL Pelobates fuscus, coccygeal portion of developing vertebral column. Fig. 13 in a Tadpole of 92 millim., from beneath. Fig. 14 in an older Tadpole of 112 millim., from the side. cc, urostyle; nc, notochord ; v.a. IX-XI, vertebral arches. 2\ times nat. size. In view of this, and of my tadpole proving to be a Pelobatoid, I eagerly availed myself of the beautiful preparations of the larval skeleton of Pelobates fuscus placed upon the market by Fritsch of Prague. Great was m y delight to find that two of the three individuals purchased from him showed the ossification in question. This and certain other genera of living Anura are somewhat remarkable for the detailed mode of development of their vertebral bodies 2 and especially for the late appearance of their centra, those structures not being developed until the arches are in an advanced and directly articulated state. The rod above referred to (cc, fig. 14), which beyond doubt gives rise to at any rate the main portion of that which Goette calls3 the periosteal component of the urostyle, arises in the interval of time between the formation of the ossific neural arches and their corresponding bony centra. The figures sufficiently show that it first appears beneath the 10th pair of arches as ordinarily enumerated (v.a. x), and that it elongates in a backward direction with the superaddition of the 11th pair (v.a. xi). There is thus recognizable at this period of growth a provisional inversion of the order of development of the parts-the ossific neural arches appearing before their corresponding centra and the ossific body of the urostyle arising prior to the first deposition of the last (1 lth) pair of arches, with which it subsequently first unites. In consideration of the conflicting opinions concerning the morphology of the "hypochordal" constituent of the urostyle4, and especially of Goette's refusal to admit this homologous either with entire vertebrae or vertebral bodies 5, this 1 Loc. cit. pp. 108-111. 2 Cf. Balfour's ' Embryology,' vol. ii. p. 556. 3 Loc. cit. p. 933, and pi. xi. fig. 196. 4 Cf. Gegenbaur, loc. cit. pp. 32-33. 5 Loc. cit. p. 393. |
