Prehension in man revisited: lesson from the monkey (Macaca fascicularis).

The manus in human is capable of performing intricate movements. To determine whether human dexterity is the result of neuromuscular co-ordination arising from a rich cortical network or due to biomechanical adaptation, the multitendoned extrinsic flexor muscles and intrinsic flexor musculature of the hand were examined in nine human cadavers and compared to those in three macaque monkeys. The flexor pollicis longus was present in all the upper limbs of the human cadavers and absent in all the upper limbs of the monkeys. An accesory origin of the flexor pollicis longus was seen in the upper limb of an Indian cadaver. The opponens pollicis which is possibly the most important intrinsic muscle of the hand was observed to be present in the manus of both human and monkey. Although the macaque monkey lacks a flexor pollicis longus, its digital dexterity has been reported to be equal to man. In this context, it would appear that neural output is the more important factor in prehensile activities.