Scanning electron microscopic observations of the canine inner ear

The sensory epithelia of the inner ear of the dog have been investigated using scanning electron microscopy (SEM). The surface appearance of the cristae ampullares of the semicircular canals and of the macula utriculi are very similar to other mammalian species. The crista ampullaris of the anterior vertical semicircular canal is divided by a non-sensory septum cruciatum, found in cats and rats but not, for example, in man. The vestibular sensory cells possess two distinct types of stereocilia, one is thick and rigid appearing, the other is thin and limp. Neither type of stereocilium is restricted to a particular hair cell type. From SEM views of the undersurface of the tectorial membrane of the cochlea we show evidence that some inner hair cell stereocilia may be attached to the tectorial membrane. This observation is made only in middle to upper cochlear regions (those subserving transduction of low frequencies of sound).