On the cloacal region of Anura in particular of larval Ascaphus

Van Dijk, D. E. (D. Eddie) (1959-12)

Thesis (DSc)--University of Stellenbosch, 1959

Published in the Annals of the University of Stellenbosch, Vol. 35, Sect. A, No.4 (1959)

Thesis

ENGLISH ABSTRACT: The ontogeny of the cloacal region of Ascaphus is described from limited larval material (beginning approximately at the stage of hind-limb bud development). A comprehensive series of Bufo angusticeps larvae and late pre-larval embryos were used for comparison. The adult and/ or late larval conditions of the cloacal region in Ascaphus, Bufo, Bombina, Leiopelma, Rana and Xenopus arc compared. The rods of Noble supporting the cloaca in Ascaphus and the tendinous sheet connecting these with the epipubis are shown to be modifications of an interfemoral ligament present, with thickened lateral margins, in all the Anura studied. The cloacal lips differentiate early in metamorphosis in Ascaphus and Bufo and bear similar relations to the interfemoral ligament in these and other Anura, so that they are apparently homologous. The posterior part of the urodaeum is lengthened in the adult male Ascaphus to form the "tail" (phallus). The hind-limb anlagen of Ascaphus appear directly beneath the spinal myomeres and immediately behind the posterior tips of the abdominal muscle cords. In Ascaphus, Bufo and Bombina the abdominal muscles (metamerically disposed in Ascaphus and Bufo) are initially attached posteriorly to the spinal myomeres but are separated from them anteriorly. lt is probable that the mm. compressores cloacae are derived from the hind-limb anlagen. In all Anura examined, including members of all the South African families, the a. ischiadica and n. ischiadicus have a small muscle (designated m. circumflexor arteriae) associated with them; it is presumably capable of compressing the artery against the nerve. The cloacal region of Ascaphus appears to be less specialized than that of Rana and Xenopus, contrary to what is generally believed for the last two genera. Bufo, particularly and Bombina have undergone less specialization.

No Afrikaans abstract available.

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