The membranous labyrinth (latin: labyrinthus membranaceus) is a system of ducts and dilatations located within the bony labyrinth of the internal ear and it contains the receptors for hearing and balance.
The membranous labyrinth is composed of two functional parts: the vestibular labyrinth and the cochlear labyrinth.
The vestibular labyrinth includes two sacs (utricle and saccule), and three semicircular ducts (anterior, lateral and posterior semicircular ducts). The utricle and saccule ar enclosed by the bony vestibule, while the semicircular ducts are lodged in the semicircular canals of the bony labyrinth. The vestibular labyrinth contains balance receptors for appreciation of the impact of gravitation (static balance) - located in the utricle and saccule, and of the impact of acceleration (kinetic balance) - located in the semicircular ducts.
The cochlear labyrinth is the content of the osseous cochlea, including the cochlear duct. The cochlear labyrinth is a fluid-filled membrane housing the Corti organ with receptors for detecting sound stimulus.
The space inside the membranous labyrinth is filled with endolymphatic fluid, while the outside of the membranous labyrinth is filled with perilymph, separating the membranous labyrinth from the walls of the bony labyrinth. In some places the structures of the membranous labyrinth are fixated to the walls of the bony capsule.