semicircular canal

:  any of the loop-shaped tubular parts of the labyrinth of the ear that together constitute a sensory organ associated with the maintenance of bodily equilibrium, that consist of an inner membranous canal of the membranous labyrinth and a corresponding outer bony canal of the bony labyrinth, and that in all vertebrates above cyclostomes form a group of three in each ear usually in planes nearly at right angles to each other—see semicircular duct