ABSTRACT
Cochleae of guinea pig, cat, and human fetus were studied under SEM. After tbe treatment with osmic and tannic acids, they were dehydrated by a critical point drier, then coated with carbon and gold, and observed under a JSM-35 scanning electon microscope.The organ of Corti looks like a spiral staircase winding around the modiolus. It is wider at apex and narrower at base. The vestibular membrane is composed of squamous epithelia covered with microvilli. The tectorial membrane is mainly composed of parallel fibrils, but at its surface and marginal region, the fibillae interwoven. There are three rows of outer hair cells (OHC) and one row of inner hair cell (IHC) in the organ of Corti, and the head plate of pillar cells is set in between both kinds of cells. The stereocilia of OHC are arranged in W-form, whereas those of IHC are in a curved arrangement. All the cells observed have microvilli, however, in some of the animal specimens, the stereocilia are irregularly arranged, damaged or entirely disappeared owing to noise exposure.In the four-month fetal cochlea, the cuticular plates of OHC looks just like velvet balls, which afterwards become W-shaped stereocilia, while on the surface of IHC, primitive hair bundles develop into a curved arrangement.Certain broken organ of Corti shows cylindrical body of OHC and its cup-like supporting structure. Phalangeal processes of Deiter ceils and OHC are obliquely arranged forming an angle. The pillar cell body is thin above and thick below, and twined with very thin nerve network.The tunnel cavity can be exposed by removing the roof structures, then longitudinal nerve fibers going along the tunnel bottom may be clearly seen. These fibers belong to the spirotunnel bundle——an efferent branch of olivo-cochlear bundle.