The cerebellum of the bullfrog tadpole (Rana catesbeiana).

The cerebellum of the premetamorphic bullfrog tadpole differs from the cerebellum of other frog species in its morphology and maturational state. The cell mass beneath the floor of the lateral recess and bordering its lateral wall that has been reported to form the auricular lobe in other species is absent, the auricular lobe abutting the medial wall of the lateral recess instead and is continuous with the corpus cerebelli. The corpus cerebelli, although immature and yet to acquire an external granular layer, is already massive and displays an incipient molecular, Purkinje cell and granular layers. Cytodifferentiation in the auricular lobe and corpus cerebelli is similar, their constituent cells being in various stages of development. Fully mature cells are absent, but a small population of Purkinje cells and glia in the auricular lobe and along the marginal zone of the corpus cerebelli show advanced development. The orientation of these Purkinje cells is parallel to the pia and appears to approximate the course of the vestibulo-lateral commissural fibers. In the ventral part of the corpus cerebelli, developing climbing fibers are present but Purkinje cells are poorly developed.