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The vestibule is the central part of the
bony labyrinth The bony labyrinth (also osseous labyrinth or otic capsule) is the rigid, bony outer wall of the inner ear in the temporal bone. It consists of three parts: the vestibule of the ear, vestibule, semicircular canals, and cochlea. These are cavities ho ...

bony labyrinth
in the
inner ear The inner ear (internal ear, auris interna) is the innermost part of the vertebrate ear The ear is the organ of hearing and, in mammals, balance. In mammals, the ear is usually described as having three parts—the outer ear T ...

inner ear
, and is situated medial to the
eardrum In the anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, ...
(tympanic membrane), behind the
cochlea The cochlea is the part of the inner ear Inner Ear (established in 2007 in Bodø, Norway) is a Norwegian record label initiated and led by the brothers and jazz musicians Tore Johansen and Roger Johansen (musician), Roger Johansen. They opene ...

cochlea
, and in front of the three
semicircular canal The semicircular canals or semicircular ducts are three semicircular In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space ...
s. The name comes from the Latin ''vestibulum'', literally an entrance hall.


Structure

The vestibule is somewhat oval in shape, but flattened transversely; it measures about 5 mm from front to back, the same from top to bottom, and about 3 mm across. In its lateral or tympanic wall is the
oval window The oval window (or ''fenestra vestibuli'' or ''fenestra ovalis'') is a membrane-covered opening from the middle ear to the cochlea The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, ...
(fenestra vestibuli), closed, in the fresh state, by the base of the
stapes The ''stapes'' or stirrup is a bone in the middle ear of humans and other animals which is involved in the conduction of sound vibrations to the inner ear. This bone is connected to the oval window by its Annular ligament of stapes, annular ligam ...
and annular ligament. On its medial wall, at the forepart, is a small circular depression, the recessus sphæricus, which is perforated, at its anterior and inferior part, by several minute holes (macula cribrosa media) for the passage of filaments of the
acoustic nerve The cochlear nerve (also auditory or acoustic neuron) is one of two parts of the vestibulocochlear nerve, a cranial nerve present in amniotes, the other part being the vestibular nerve. The cochlear nerve carries auditory sensory information from th ...
to the saccule; and behind this depression is an oblique ridge, the
crista vestibuli A crista (; plural cristae) is a fold in the inner mitochondrial membrane, inner membrane of a mitochondrion. The name is from the Latin for ''crest'' or ''plume'', and it gives the inner membrane its characteristic wrinkled shape, providing a larg ...
, the anterior end of which is named the pyramid of the vestibule. This ridge bifurcates below to enclose a small depression, the fossa cochlearis, which is perforated by a number of holes for the passage of filaments of the acoustic nerve which supply the vestibular end of the ductus cochlearis. The orifice of the aquæductus vestibuli is the hind part of the medial wall; it extends to the posterior surface of the petrous portion of the
temporal bone The temporal bones are situated at the sides and base of the skull The skull is a bone A bone is a rigid tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function ...

temporal bone
. It transmits a small vein and contains a tubular prolongation of the membranous labyrinth, the
endolymphatic duct From the posterior wall of the saccule a canal, the endolymphatic duct, is given off; this duct is joined by the ductus utriculosaccularis, and then passes along the aquaeductus vestibuli and ends in a blind pouch (endolymphatic sac) on the posterio ...
, which ends in a cul-de-sac between the layers of the
dura mater Dura mater is a thick membrane made of dense irregular connective tissue that surrounds the brain and spinal cord. It is the outermost of the three layers of membrane called the meninges that protect the central nervous system. The other two mening ...
within the cranial cavity. On the upper wall or roof, there is a transversely oval depression, the recessus ellipticus, separated from the recessus sphæricus by the crista vestibuli already mentioned. The pyramid and adjoining part of the recessus ellipticus are perforated by a number of holes (macula cribrosa superior). The apertures in the pyramid transmit the nerves to the utricle; those in the recessus ellipticus are the nerves to the ampullæ of the superior and lateral semicircular ducts. Behind, the five orifices of the semicircular canals can be found. In the frontal view, there is an elliptical opening which communicates with the scala vestibuli of the cochlea.


Additional images

File:Sobo 1909 783.png, Right osseous labyrinth (lateral view). File:Gray923.png, The cochlea and vestibule (view from above). File:Gray919.png, Chain of ossicles and their ligaments, seen from the front in a vertical, transverse section of the tympanum. (Vestibule visible at center right.) File:Sobo 1911 773.png, Internal liquid structures of the cochlea and semicircular ducts, vestibule at centre.


References


See also

*
Vestibular system The vestibular system, in vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, ...
Ear {{Portal bar, Anatomy