hand, terminal part of the forelimb in primates. The human hand consists of the wrist, palm, four fingers, and thumb. In humans and other primates, the thumb is opposable, i.e., it can be moved into a position opposite to the other four digits. Opposable thumbs make possible precise movements such as grasping small objects. In vertebrates other than humans, the primary function of the hand is locomotion; the human hand, due to the evolutionary development of bipedalism, is freed for manipulative tasks. There are 27 bones in the human hand. The wrist, which joins the hand to the forearm, contains eight cubelike bones arranged in two rows of four bones each. The metacarpus, or palm, is composed of five long metacarpal bones. Fourteen phalangeal bones constitute the four fingers and thumb (three in each finger, two in the thumb). Ligaments interconnect the bones of the hand. The bones of the digits are anchored to muscles in the hand and to muscles in the arms and shoulders, through connections to tendons, permitting a wide range of movements. Among humans, the undersides of the fingers and palms have distinctive ridges, which improve grip and can be used as identification marks.
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