Surface Structures of the Human Vestibular Sensory Regions.

The hair bundles and other surface organelles of the human vestibular sensory regions have been studied with SEM and TEM. The material was taken from individuals of different ages, from the fetal period to old age. The hair bundles have a remarkably mature appearance in fetuses three to four months old. Each hair bundle consists of one kinocilium and of many stereocilia of different length. Some hair bundles are shorter than the majority. There are indications that these short hair bundles, which are especially numerous at the edges of the maculae, belong to type II sensory cells. In old individuals, laminated inclusions are often seen in the cytoplasm close to the cuticular plate. Each supporting cell is equipped with microvilli and a solitary kinocilium in the fetal period. In adults these microvilli are shorter and more scanty, and the kinocilium is usually missing.