Hand

A hand is a prehensile, multi-digited appendage located at the end of the forearm or forelimb, primarily found in primates such as humans, chimpanzees, monkeys, and lemurs. A few other vertebrates, like the koala—which possesses two opposable thumbs on each hand and fingerprints remarkably similar to humans—and the raccoon, which lacks opposable thumbs, are also commonly described as having hands. The technical anatomical term for the distal portion of a forelimb is the manus, and some evolutionary anatomists use "hand" more broadly to refer to the forelimb’s digit-bearing appendage, such as when comparing the three digits of a bird’s hand to those of a dinosaur’s hand.

The human hand typically has five digits: four fingers and one thumb, though these are often collectively called five fingers. It contains 27 bones, excluding sesamoid bones (which vary in number among individuals). Of these, 14 are phalanges (proximal, intermediate, and distal) for the fingers and thumb. The metacarpal bones connect the fingers to the eight carpal bones of the wrist. Fingers house some of the densest nerve endings in the body, providing the richest tactile feedback and the greatest positioning capability, making the sense of touch intimately linked with the hands. Like other paired organs, each hand is dominantly controlled by the opposite brain hemisphere, so handedness—the preferred hand for single-handed tasks like writing—reflects individual brain function. Hands are crucial in human body language and sign language, and the ten digits of two hands, along with the twelve phalanges of four fingers (touchable by the thumb), have inspired number systems and calculation techniques.

The hand is located at the distal end of each arm. Its areas include the palm (volar), which has dermal papillae for friction and fingerprints; the opisthenar (dorsal) area; and the heel of the hand, which bears pressure during support activities like handstands. The five digits include the thumb (opposable, allowing it to be brought opposite the fingers) and four fingers: index, middle, ring, and little finger. The skeleton comprises eight carpal bones in proximal and distal rows, five metacarpals, and fourteen phalanges, with small sesamoid bones at the palmar aspect of the first metacarpophalangeal joints.