An analysis of the muscular limitation on opposability in seven species of Cercopithecinae

Cercopithecinae have long been considered to have a manus capable of opposition. Observations of manipulation in seven quadrupedal species of Cercopithecinae show that three opposable grips are used, ranging from the ultimate refinement of the “precision grip,” the refined opposition, where contact is made between the distal pads of the first digit (d1) and the second digit (d2), to the cup, where the pollex is equidistant from, and presses an object against, the palmar pads of the other digits. The most frequently used hand position was the quasi‐opposition, where the distal pad of d1 contacts d2 anywhere along its lateral aspect. Dissections of the muscles of the pollex showed that in all the species studied refined opposition depends on the abductor brevis and opponens pollicis. In general the other pollical muscles, which enhance opposition in man, are limiting factors on this movement. The differences among the species, however, tend to reflect use of the hand. Thus, those species subsisting principally on a diet of seeds and grasses were found to have the highest frequency of refined opposition, and their pollical anatomy shows a muscular configuration facilitating opposition. The suggestion is made that manipulation as in procuring, conveying and preparing food may have been a more important adaptive pressure than locomotion in retention of the generalized form of the cercopithecine hand.