To study the sense of spatial orientation, understanding the coordinate system of the labyrinth is indispensable. The 100-year-old stereoscopic photograph of the labyrinth shows the three semicircular canals arranged as if a three-coordinate axis. Behavioral observation of canal nerve stimulation 40 years ago disclosed that electrical stimulation of the canal nerve moved the eyes along the canal when the head was fixed. When the head was free to move, it moved the head in the same direction, and it moved the animal in space when the animal was free to move.Stereo-measurements of the labyrinth determined that the semicircular canals are not orthogonal to each other, and the synergistic pairs of canals in the right and left ears are not on one plane. The semicircular canal nerves sent information regarding head rotation velocity on the non-orthogonal canal coordinate axis. A three-dimension analysis of the vestibulo-ocular reflex (VOR) before and after canal plugging enabled precise measurements of semicircular canal contribution to VOR. The summed gain and phases of plugged VOR were comparable to the VOR of normal; LC (four vertical canals plugged) +VC (bilateral lateral canals plugged) =Normal, and RALP+LARP (sum of one pair of vertical canals intact) =VC, however, rotation in light did not change after plugging. These findings indicate that a semicircular canal coordinate system is firm and does not adapt after inactivation, although, sufficiently compensated by vision while moving in light.