Parasympathetic postganglionic nerve fibers in the fungiform papillae of the bullfrog, Rana catesbeiana.

An investigation was made of the precise origin of the unmyelinated nerve fibers in the fungiform papillae of the bullfrog's tongue. Some unmyelinated nerve fibers in the fungiform papillae originate from the parasympathetic postganglionic cells in the glossopharyngeal nerve. Axonal enlargements of the parasympathetic nerve fibers were in close contact with the Merkel-like basal or supporting cells in the taste disk. These results seem to provide morphological evidence for the existence of an efferent control system in the taste disk.