A comprehensive analysis of the transient north-south anisotropy that is a characteristic feature of Forbush decreases has revealed that the direction of axial anisotropy is determined by the inclination of the associated interplanetary shock wave with respect to the ecliptic plane. The study included all recorded cosmic ray events (15) for which the sense of the anisotropy vector could be determined by a rigorous statistical procedure and for which the associated shock orientation is known. In contrast, similar examination of the same set of events showed that there is no correlation between the sense of the north-south anisotropy and either the heliolatitude of the associated solar flare or the inclination of the interplanetary magnetic field. An additional investigation of the collection of heretofore puzzling events during which the direction of anisotropy flips suddenly has shown that the reversal is associated with the arrival of a second shock, presumably having an inclination that is opposite to that of the earlier one associated with the onse of the Forbush decrease. These results provide new insight into the key role played by shocks in the transient modulation mechanism.