An Analysis of the Muscular Limitation on Opposability in Seven Species of Cercopithecinae FRANCES D. BURTON Deportment of Anthropology, University of Toroltto, Toronto 5, Ontario, Canada KEY WORDS Primates . Musculature . Opposition . Adaptation. ABSTRACT 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 (dl) 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 dl 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 loco- motion in retention of the generalized form of the cercopithecine hand. One of the factors most influencing the evolution of man has been his ability to manipulate objects. The phylogenetic de- velopment culminating in this ability has received relatively little attention. The majority of studies on the non-human hand have concentrated on it as a part of the locomotor complex (e.g., Keith, 1894; Jouffroy and Lessertisseur, '60; Ox- nard, '63; Bishop, '64; Tuttle, '67). The major exceptions include the two papers by Alison Bishop on the Prosimii ('62, '64), both behavioral studies, Hall and Mayer's work on Erythrocebus patas ('66), and the work of J. R. Napier since 1955, which has concentrated on cer- tain aspects of the anatomy of the hand of non-human primates in general while including behavioral aspects. The progres- sion from convergent (represented by Tar- sier) to prehensile (represented by Cal- lithrix) to pseudo-opposable (represented by Cebus) to opposable (represented by Cercopithecoidea, Pongidae and Homo) AM. J. PHYS. ANTHROP., 36: 16S188. (Napier, '61; Napier and Napier, '67) has, according to Napier, led to a hand capa- ble of opposition, and its refinement, the precision grip. Opposition is defined as a combination of movements - flexion, abduction and conjunct rotation - which rotate the thumb on its longitudinal axis so that the palmar surface of the tip of the thumb comes in contact with the palmar pads of the other digits (Duchenne, 1858, cited in Kaplan, '53; du Bois Reymond, 1895; Schultz, '26; Haines, '44; LeGros Clark, '59; Napier, '60; Jones, '67). The ability to oppose is intrinsic to the cercopithecine hand due to the carpometacarpal saddle joint. The degree to which opposable grips are used, however, varies from species to species within the taxon. The limitations on the use of opposi- tion may coincide with two factors: the type and nature of foods eaten in the wild 1 Editor's Note: The photographs were taken under field conditions. 169