Ultrastructure of the Basilar Papilla, An Auditory Organ in the Bullfrog

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Abstract
The basilar papilla is one of two auditory organs found in the frog's inner ear. Examination of the papilla in the bullfrog, Rana catesbeiana, by light and electron microscopy has confirmed earlier descriptions of its gross morphology and revealed new details of its fine structure. The papilla is a tubular evagination of the saccule, terminating in a thin contact membrane which separates endolymphatic and perilymphatic spaces. Its sensory epithelium occupies a crest extending halfway around the tube and is surmounted by a tectorial membrane. Between 300 and 500 myelinated nerve fibers synapse with about 60 hair cells. Extending from the hair cells are sensory hair bundles, lodged in canals in the tectorial membrane. Each bundle consists of a group of stereocilia and a single asymmetrically placed kinocilium located on the side of the bundle facing the contact membrane. Each hair cell synapses at its base with several afferent terminals, but efferent synapses have not been found.