Development of vestibular receptor surfaces in human fetuses.

The development of human vestibular receptors was studied between the 7th and 14th gestational weeks using scanning electron microscopy. The development phase appeared to last longer than previously described. At 7 weeks, no receptors were individualized, the vestibular epithelium was plicated, and scarce nascent hair bundles could be seen grouped in a small area. At 8 weeks, all receptors were well differentiated. Modifications in crista shapes were evaluated qualitatively and quantitatively along the length of their profile. Their growth occurred in two quick steps with a pause between the 9th and 12th weeks, during which growth slowed and a transformation occurred. In the utricle, the epithelium decreased in thickness, and this process underwent a pause between the 8th and 11th weeks. These results demonstrate pauses in the maturation process of the vestibular receptors and show that the utricles develop one week in advance of the cristae. At 14 weeks, all receptors had an adult profile, but the cristae had only reached 55 per cent of their adult size. The ciliary apparatus appeared to be nearly mature in the utricle but was still growing in the cristae. The differentiation of ciliary tufts in the cristae displayed an apex-base gradient. These developmental patterns were compared with those described in the mouse.