Embryogenesis of the inner ear - I. Development and differentiation of the mammalian crista ampullaris in vivo and in vitro

The embryonic development of the crista ampullaris in the CBA/CBA mouse was followed comparatively in vivo and in vitro after explantation of the 13th gestational day otocyst. Special attention was paid to hair cell differentiation. In general the in vivo and the in vitro groups of inner ears showed a similar morphological maturation of hair cells on the ultrastructural level. The first sign of hair cell differentiation occurred on the 14th day in vivo and after 1 day in culture showing a thickening of microvilli presumably indicating the development of future sensory hairs. On the 16th day or after 3 days of in vitro culture the sensory hairs were regularely arranged with the kinocilium located at the cell periphery. Afferent nerve endings were identified on the 17th gestational day and some nerve terminals were suspected to be of efferent character appearing on the 18th day. On the day of birth there did not occur complete nerve chalices but a differentiation of hair cells into type I and type II was indicated on the 19th gestational day by a slight difference in hair cell configuration and extension of innervation.