Embryogenesis of the inner ear. IV. Post-natal maturation of the secretory epithelia of the inner ear in correlation with the elemental composition in the endolymphatic space.

The rise of the potassium concentration in the endolymphatic space occurred between the 4th and 8th day after birth (DAB). During this time morphological maturation of the stria vascularis was ended. The increasing concentration of potassium in the developing endolymph parallelled in the vestibular and cochlear parts of the labyrinth. The dark cell epithelium surrounding vestibular organs was, however, ultrastructurally mature at birth except for an increase of the number of intercellular digitations toward the basal membrane maturing during the first days postpartum. The maturation of endolymph thus took place prior to the development of the endocochlear potential.