vestibular duct vestibular duct the vestibular duct or scala vestibuli is a perilymph-filled cavity inside the cochlea of the inner ear that conducts sound vibrations to the cochlear duct. not to be confused with bulb of vestibule. vestibular ductinner ear, with vestibular duct labeled near bottom.cross section of the cochlea.detailsidentifierslatinscala vestibulimeshd054738ta98a15.3.03.043ta26968fma61269anatomical terminology it is separated from the cochlear duct by reissner's membrane and extends from the vestibule of the ear to the helicotrema where it joins the tympanic duct. additional images the cochlea and vestibule, viewed from above. transverse section of the cochlear duct of a fetal cat. interior of right osseous labyrinth. diagrammatic longitudinal section of the cochlea.