part of vestibular system semicircular canal BTO:0003383 BrendaTissueOBO Three membranous semicircular tubes contained in the bony labyrinth of the inner ear. They are concerned with equilibrium and the interpretation of the bodys position in space. The three canals are set anterior, posterior, and lateral, at right angles to each other and are situated superior and posterior to the vestibule. ductus semicirculares