What space lies between the osseous and membranous labyrinths, and what fluid fills it?

The perilymphatic space (spatium perilymphaticum) lies between the walls of the bony and membranous labyrinths and is filled with perilymph.

Where is the endolymphatic sac anatomically located?

The endolymphatic sac (saccus endolymphaticus) is located within the dura mater on the posterior surface of the petrous part of the temporal bone.

How are the macula of the utricle and the macula of the saccule oriented relative to each other?

The macula of the utricle lies in the floor of the utricle roughly parallel to the cranial base, whereas the macula of the saccule is oriented vertically on the medial wall of the saccule.

Through which anatomical channel does the cochlear duct communicate with the saccule?

The cochlear duct communicates with the saccule via the uniting duct (ductus reuniens).

Where is endolymph produced?

Endolymph is produced by the vascular stria (stria vascularis), which forms the outer wall of the cochlear duct.

What is the function of the utricle and saccule?

Their sensory maculae contain statoconia (otoliths), which mediate the perception of linear acceleration and head position relative to gravity.

What is the function of the ampullary crests?

The ampullary crests, located within the membranous semicircular ducts, specialize in detecting angular (rotational) acceleration.

What constitutes the peripheral auditory receptor apparatus?

It is the spiral organ (organ of Corti), located on the basilar membrane of the cochlear duct. It contains hair cells that convert sound vibrations into nerve impulses.

Home › Human Anatomy › Membranous Labyrinth of the Inner Ear

Membranous Labyrinth of the Inner Ear

Labyrinthus membranaceus

For medical students2 min readUpdated 2026-10-10

The membranous labyrinth is a complex system of interconnecting ducts and cavities located within the osseous labyrinth of the inner ear. It closely mirrors the shape of the bony framework, though it is smaller in size and filled with a specialized fluid called endolymph.

LocationWithin the osseous labyrinth

Fluid contentEndolymph

Sensory apparatusReceptors for hearing and balance

Main componentsUtricle, saccule, semicircular ducts, and cochlear duct

General Overview

The membranous labyrinth (labyrinthus membranaceus) forms a closed system suspended inside the osseous labyrinth. Its primary feature is that it topographically mimics the contours of the bony labyrinth, yet is considerably smaller.

The entire internal cavity of this structure is filled with fluid—endolymph.

Anatomo-functionally, the membranous labyrinth is divided into several key components, each serving a distinct physiological role:

utricle (utriculus);
saccule (sacculus);
membranous semicircular ducts (ductus semicirculares);
cochlear duct (ductus cochlearis).

Vestibule: Utricle and Saccule

Two major expansions of the membranous labyrinth are located within the vestibule, responsible for vestibular functions.

The utricle (utriculus) lies in the elliptic recess (recessus ellipticus). The saccule (sacculus) is located in the spherical recess (recessus sphericus).

Specialized sensory areas called maculae are situated on the inner surface of these structures:

macula utriculi;
macula sacculi.

These regions contain otolith crystals known as statoconia (statoconia). Their main function is to detect linear acceleration and register changes in head position in space.

Both structures (utricle and saccule) are interconnected via the utriculosaccular duct (ductus utriculosaccularis). This duct continues as the endolymphatic duct (ductus endolymphaticus), which terminates blindly in the endolymphatic sac (saccus endolymphaticus).

Membranous Semicircular Ducts

The membranous semicircular ducts (ductus semicirculares) lie within their corresponding osseous semicircular canals.

Each of the three ducts features a characteristic dilation at one end called the membranous ampulla (ampulla membranacea). Inside the ampullae are sensory structures termed ampullary crests (crista ampullaris). Unlike the maculae of the utricle and saccule, the receptors of the ampullary crests specialize in detecting angular acceleration (rotational movements).

Cochlear Duct and Spiral Organ

The cochlear duct (ductus cochlearis) is located within the spiral canal of the cochlea (canalis spiralis cochleae). On cross-section, this duct has a distinct triangular shape.

The walls of the cochlear duct are formed by the following structures:

Basilar membrane (membrana basilaris) — the floor/lower wall.
Vestibular membrane or Reissner's membrane (membrana vestibularis) — the roof/upper wall.
Outer wall — formed by the vascular stria (stria vascularis). The vascular stria is responsible for secreting (producing) the endolymph that fills the membranous labyrinth.

The basilar membrane supports the primary organ of hearing, the spiral organ (organum spirale), also known as the organ of Corti. It serves as the peripheral auditory receptor apparatus.

The spiral organ consists of:

inner and outer hair cells (cellulae pilosae internae et externae), which act as mechanoreceptors;
supporting cells;
tectorial membrane (membrana tectoria), which overhangs the hair cells.

Mnemonic

Mnemonic for location: The Saccule lies in the Sphericus recess — both start with the letter "S".

Frequently asked questions

What space lies between the osseous and membranous labyrinths, and what fluid fills it?: The perilymphatic space (spatium perilymphaticum) lies between the walls of the bony and membranous labyrinths and is filled with perilymph.
Where is the endolymphatic sac anatomically located?: The endolymphatic sac (saccus endolymphaticus) is located within the dura mater on the posterior surface of the petrous part of the temporal bone.
How are the macula of the utricle and the macula of the saccule oriented relative to each other?: The macula of the utricle lies in the floor of the utricle roughly parallel to the cranial base, whereas the macula of the saccule is oriented vertically on the medial wall of the saccule.
Through which anatomical channel does the cochlear duct communicate with the saccule?: The cochlear duct communicates with the saccule via the uniting duct (ductus reuniens).
Where is endolymph produced?: Endolymph is produced by the vascular stria (stria vascularis), which forms the outer wall of the cochlear duct.
What is the function of the utricle and saccule?: Their sensory maculae contain statoconia (otoliths), which mediate the perception of linear acceleration and head position relative to gravity.
What is the function of the ampullary crests?: The ampullary crests, located within the membranous semicircular ducts, specialize in detecting angular (rotational) acceleration.
What constitutes the peripheral auditory receptor apparatus?: It is the spiral organ (organ of Corti), located on the basilar membrane of the cochlear duct. It contains hair cells that convert sound vibrations into nerve impulses.

Go deeper

Cellular organization of the spiral organ (organ of Corti)
Endolymph circulation and the physiological role of the saccus endolymphaticus
Histology of hair cells and supporting cells
Anatomical relationships between membranous structures and the osseous labyrinth