| Summary: | Thesis (DSc)--University of Stellenbosch, 1959 === Published in the Annals of the University of Stellenbosch, Vol. 35, Sect. A, No.4 (1959) === 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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