It is believed that the saccade system uses the horizontal and vertical Cartesian coordinates, based on the clinical and lesion studies. However, the present study revealed that the saccade system uses the semicircular canal coordinate rather than the horizontal and vertical coordinate. Using intracellular recording techniques, we analyzed synaptic connections from the superior colliculus (SC) to vertical ocular motoneurons (MNs) and tectoreticular saccade neurons (TRNs) in the opposite SC in anesthetized cats. TRNs in the medial and lateral SC activated superior rectus and inferior oblique MNs and inferior rectus and superior oblique MNs via the riMLF, respectively. These innervation patterns are similar to those in the VOR from the anterior and posterior canal, respectively. Stimulation of the SC and recording from TRNs in the opposite SC showed that inhibitory commissural connections exist between the medial (lateral) SC representing upward (downward) saccades side and the opposite lateral (medial) SC representing downward (upward) saccades. This pattern of reciprocal inhibition between the SCs is very similar to that seen between the bilateral vestibular nuclei in the vertical VOR evoked by head rotation in the plane of the anterior canal on one side and the posterior canal on the other. These similarities of the motoneuronal innervation patterns and the commissural inhibitions in the VOR and saccade systems strongly suggest that both systems use the common semicircular canal coordinate. However, if the saccade system uses the semicircular canal coordinate, then the saccade system may violate Listing's Law (LL), because it is well known that the VOR does not obey LL. We found a strong commissural excitation between the symmetrical parts of the rostral SCs; TRNs in the medial and lateral SC received commissural excitation from the opposite medial and lateral SC, respectively. When TRNs in the medial (lateral) SC on both sides are activated by commissural excitation, torsional components of individual eyes may cancel each other and upward (downward) saccades occur. Therefore, these tectotectal commissural excitatory connections are considered to minimize torsional eye movements and help to maintain LL in the saccadic system.