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Urostyle, ū′rō-stīl, n. a prolongation backward of the last vertebra.—adj.

The main adaptive specializations of Anura, however, including loss of the adult tail, extreme reduction in number of vertebrae, formation of urostyle, elongation of the ilium and lengthening of the hind legs, must have appeared at a later time than the separation of that order from any possible common stem with Urodela, although they are only partially developed in the Triassic Protobatrachus.

Basiventral arcualia have been supposed to be represented by the hypochord, a median rod of cartilage beneath the shrinking notochord in the postsacral region, which at metamorphosis ossifies to produce the bulk of the urostyle.

Urostyle, the last vertebra, lying in the median line, a long, slender, blade-like bone, really formed by the fusion of several vertebr�.

As the tadpole approaches the frog stage the vertebral column in the tail is rapidly absorbed, and its vestiges appear in the adult as the urostyle.