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One of three membranous tubes forming a part of the vestibular labyrinth of the inner ear. They lie within the semicircular canals and bear corresponding names: anterior, posterior, and lateral. The semicircular ducts originate from the utricle as a single common tube (crus communale). The three ducts then branch, and each follows the course of a different bony semicircular canal. At their far ends the ducts widen into an ampulla that contains a specialized endothelium that is sensitive to motion of the endolymph. Axons from receptor cells in these sensory epithelia transmit motion information to the brain via the vestibular division of the vestibulococchlear nerve (CN VIII). See: labyrinth for illus.
See also: duct