Fig. 4.

Grasping with digits, pressing a grasped object against an abutment. In the feet of primates, this is commonly the hallux; in the hands, the pollex (a) may be replaced by (b) the soft tissue over the heads of the metacarpals, or the thenar plus hypothenar eminences. Increased length of the autopodia (hands and feet), which increases the span of the grip, nevertheless reduces the contact pressure (c). Reduced width of the hand (d) leads to higher pressure over the contact area. Because friction depends on the contact pressure, this allows the transmission of greater rotating moments.