Anterior semicircular canal - Canalis semicircularis anterior
The anterior (superior) semicircular canal (canalis semicircularis anterior), 15 to 20 mm. in length, is vertical in direction, and is placed transversely to the long axis of the petrous portion of the temporal bone, on the anterior surface of which its arch forms a round projection.
It describes about two-thirds of a circle. Its lateral extremity is ampullated (Anterior bony ampulla), and opens into the upper part of the vestibule; the opposite end joins with the upper part of the posterior canal to form the common bony limb (crus commune), which opens into the upper and medial part of the vestibule.
This definition incorporates text from a public domain edition of Gray's Anatomy (20th U.S. edition of Gray's Anatomy of the Human Body, published in 1918 – from http://www.bartleby.com/107/).