Light and electron microscopic studies of the basilar papilla in the duck, Anas platyrhynchos. II. Embryonic...

The intent of this study was to describe certain morphological aspects of cytodifferentiation of the basilar papilla in the duck, Anas platyrhynchos. The duck, with a longer incubation period than that of the chicken, has proven useful in identifying the earliest morphological changes during cyto-differentiation of the basilar papilla. Most of these changes occur first at the neural margin of the presumptive genu, at the site of initial contact by cochlear nerve fibers. A wave of differentiation of hair cells radiates abneurally, proximally, and distally, concurrent with the establishment of afferent innervation. Extracellular channels form in the papilla between cell bases just before the nerve fibers penetrate the basal lamina. Nerve fibers abut hair cell bases in the genu at the time the hair cells separate from the basal lamina on day 9. Hair cell bases contain granular vesicles and lie among the nuclei of supporting cells on day 10. Synaptic bodies are present opposite nerve endings on day 11. Efferent nerve endings appear on short hair cells in the genu on day 15 and on tall hair cells on day 17.