Structure
The bony labyrinth is the rigid bony outer wall of the inner ear inside the petrous part of the temporal bone. It appears as the densest portion of the temporal bone on radiographic imaging.
The bony labyrinth consists of three parts, the cochlea, vestibule, and semicircular canals (anterior, posterior and lateral). These contain a clear fluid, the perilymph, in which the membranous labyrinth is situated.
The cochlea is concerned with hearing. It is a long, tube-like canal, which is coiled around a bony pillar (the modiolus) to impart a shell-like appearance to it. The modiolus contains vessels and cochlear nerve branches. The spiral canal of the cochlea begins at the vestibule and makes 2.5 turns around the modiolus.
The vestibule of the bony labyrinth is a chamber which encloses both utricle and saccule. The vestibular chamber contains an oval window in its lateral wall. The base of the stapes (a middle ear ossicle) attaches to the oval window.
The semicircular canals lie posterosuperior and lateral to the vestibule, into which they open at five different locations. Each canal forms two-thirds of a circle and is dilated at one end to form a swelling called the bony ampulla.
Related parts of the anatomy
Key Features & Anatomical Relations
The vestibule is in communication with the bony cochlea anteromedially, the semicircular canals posterosuperior and laterally, and with the posterior cranial fossa by the vestibular aqueduct. The vestibular aqueduct contains the endolymphatic duct and opens on the petrous part of temporal bone, posterolateral to the internal acoustic meatus. Lodged within the vestibule are the utricle and saccule (parts of membranous labyrinth).
The large basal turn of the cochlea produces an elevation called the promontory inside the posterior wall of the middle ear/tympanic cavity. The bony cochlea houses the cochlear duct, which divides the bony cochlea into two channels, the scala vestibuli above and the scala tympani below.
The semicircular canals lie in three different planes (anteroposterior, side-to-side, and horizontal) and are positioned at right angles to each other (Spoor & Zonneveld, 1998)
References
Spoor, F. & Zonneveld, F. (1998) Comparative review of the human bony labyrinth. American Journal of Physical Anthropology, 107(S27), 211-251.
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Bony Labyrinth
The mammalian inner ear is anatomically defined by the bony labyrinth, a hollow periosteum-lined structure within the temporal bone, and consists of hearing (cochlear) and balance (vestibular) organs.
