Movie 4.

Animation of a horse, then dog, hindlimb with horizontal straight-line motion of the foot under the hip and vertical limb forces supported by a series of isometric tension elements (red lines) that broadly match the cranial femoris (early stance), rectus femoris (midstance) and tensor fascia latae (late stance) and result in a series of Watt's 6-bar linkages. See Figure 5. Note in early stance the cross-over link of the proximal 4-bar linkage formed by the biceps femoris couples limb retraction with limb shortening; and the uncrossed link of the tensor fascia latae, loaded in late stance, couples limb retraction with limb extension.