The fully developed oral disc of tadpoles of Bufo regularis consists of dorsal and ventral labia bearing, respectively, two and three ridges with numerous horny denticles having a dental formula , many lateral papillae on the dorsal and ventral labia that may have a sensory function, and a horny beak provided with jaw sheath serrations. At metamorphosis, these structures regress and disappear. Keratinization of the labial denticles and the beak serrations of the labial teeth occurs by the activity of the tonofilaments, while keratinization of the beak serration takes place by the cytoplasmic free ribosomes.