The three semicircular canals (SCCs) are components of the bony labyrinth within the petrous temporal bone, along with the cochlea and vestibule. They contain the semicircular ducts, part of the membranous labyrinth which are responsible for kinetic balance.
There are three semicircular canals on each side, the superior, posterior and lateral canals, each forming two-thirds of a full circle, which are oriented perpendicular (at right angles) to each other.
The lateral semicircular canal opens directly into the vestibule, whilst the superior and posterior semicircular canals form a common crus before entering the vestibule. They have differing and variable lengths but uniform diameters of ~1 mm.
Superior (anterior) semicircular canal (SSCC)
- oriented in the vertical plane perpendicular (transverse) to the long axis of the petrous temporal bone
- it lies under the arcuate eminence on the anterior surface of the petrous temporal bone
- hair cells of the superior semicircular duct supplied by the superior division of the vestibulocochlear nerve (CN VIII)
Posterior semicircular canal (PSCC)
- oriented in the vertical plane parallel to the long axis of the petrous temporal bone
- hair cells of the posterior semicircular duct supplied by the inferior division of CN VIII
Lateral (horizontal) semicircular canal (LSCC)
- oriented 30° to the horizontal
- shortest of the semicircular canals
- hair cells of the lateral semicircular duct supplied by the superior division of CN VIII