Vestibule

The vestibule (Latin: vestibulum labyrinthi, vestibulum auris) is the central part of the bony labyrinth of the internal ear that houses the utricle and saccule of the membranous labyrinth. The vestibule is oval-shaped.

Structure of the vestibule

The lateral wall of the vestibule is projected to the tympanic cavity and has two openings: the oval window (or vestibular window, Latin: fenestra vestibuli) and the round window (or cochlear window, Latin: fenestra cochleae). The oval window is the upper opening closed by the base of the stapes. The round window is the lower opening in the lateral wall of the vestibule, and it is closed by the secondary tympanic membrane.

The medial wall of the vestibule has two depressions - spherical recess and elliptical recess - that are separated by a ridge called the vestibular crest. The spherical recess is located anteriorly and is occupied by the saccule. The elliptical recess is the posterior depression in the medial wall of the vestibule, and it is occupied by a portion of the utricle between the posterior ampulla and common crus.

The vestibule sends information to the posterior cranial fossa via the vestibular aqueduct. The vestibular aqueduct is a membranous structure that starts from the vestibule, then goes through the temporal bone, and ends with an opening on the posterior surface of the petrous portion of the temporal bone. The orifice of the vestibular aqueduct is a part of the medial wall. The aqueduct contains a small vein and a tubular extension of the membranous labyrinth, the endolymphatic duct.

The anterior wall of the vestibule has an opening connecting the vestibule to the spiral canal of the cochlea. The posterior wall of the vestibule has five openings for the semicircular canals: two for the lateral semicircular canal, one for the anterior and one for the posterior semicircular canal, and one for the common crus of the anterior and posterior semicircular canals.