Comparative morphology of skeletal muscles in man and macaque

The size of skeletal muscle fibre are differentiated into thicker, and thinner fibres by the muscle functions, the former producing more force, the latter fine movements. Histochemically, fibres can also be divided in the thicker, "white", last-twitch variants and the thinner, "red", slow-twitch fibres. The present study investigates the fibre distribution in several muscles of humans, macaques, and (partly) chimpanzees. In the mono-articular muscles of the thigh, in the m. triceps surae, and in the m. tibialis anterior, the macaques have thinner and less numerous fibres than humans. The intrinsic foot muscles of macaques contain fewer fibres than those of man, and the thenar group as well as the interossei are stronger developed than in humans. The latter possess relatively heavy flexors and extensors of the elbow joint; in macaques (and more so in chimpanzees) the forearm muscles are strongly developed. The laryngeal muscles in humans contain a higher percentage of "red" fibres than those in macaques, which have more "white" fibres, while all are thinner than in humans. The outstanding trait in humans is the low number of laryngeal muscle fibres which are innervated by a single nerve fibre. The differences found can be related to the diverging locomotor and vocal hehavior of the respective forms.