The receptors for the senses of equilibrium and hearing are housed within a collection of fluid filled tubes and chambers known as the membranous labyrinth. The membranous labyrinth is lodged within the bony labyrinth

Bony labyrinth

The Bony labyrinth or osseous labyrinth consists of three parts: the vestibule, semicircular canals, and cochlea. These are cavities hollowed out of the substance of the bone, and lined by periosteum; they contain a clear fluid, the perilymph, in which the membranous labyrinth is situated....

 and has the same general form; it is, however, considerably smaller and is partly separated from the bony walls by a quantity of fluid, the perilymph

Perilymph

Perilymph is an extracellular fluid located within the cochlea in two of its three compartments: the scala tympani and scala vestibuli. The ionic composition of perilymph is comparable to that of plasma and cerebrospinal fluid...

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In certain places, it is fixed to the walls of the cavity.

The membranous labyrinth contains fluid, the endolymph

Endolymph

Endolymph is the fluid contained in the membranous labyrinth of the inner ear. It is also called Scarpa's fluid, after Antonio Scarpa.-Composition:...

, and on its walls the ramifications of the acoustic nerve are distributed.

Within the osseous vestibule, the membranous labyrinth does not quite preserve the form of the bony cavity, but consists of two membranous sacs, the utricle, and the saccule

Saccule

The saccule is a bed of sensory cells situated in the inner ear. The saccule translates head movements into neural impulses which the brain can interpret. The saccule is sensitive to linear translations of the head, specifically movements up and down...

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The membranous labyrinth is also the location for the receptor cells found in the inner ear.