Fig. 4. Graphs of vertical translations (dotted lines) and pitch rotations (solid lines) of the head during single representative cycles of (A,B) walks and (C,D) gallops by (A,C) hanumans and (B,D) bonnets. Horizontal lines below each graph depict the support phases of the left hind limb (LH), left forelimb (LF), right forelimb (RF) and right hind limb (RH). Note that the phase relationship between head translation and head rotation is variable during the walk cycle, ranging from nearly 180° out of phase to more closely in phase. By contrast, head translation and rotation are nearly in phase over most of the gallop cycle, with small counter rotations occurring primarily when the head reaches maximal heights and depths of translation. Also note that in the depicted hanuman walk cycle (A), the head pitched downward (>20°) throughout the cycle as the monkey looked down at the support surface. In the remaining three cycles depicted (B–D), by contrast, the monkeys rotationally stabilized (<20°) their heads.