(sem'ē-sĭr'kyū-lăr kă-nalz' bō'nē lab'i-rinth) The organ of balance; the three bony tubes in the labyrinth of the ear within which the membranous semicircular ducts are located; they lie in planes at right angles to each other and are known as anterior semicircular canal, posterior semicircular canal, and lateral semicircular canal.