Fourteen phalanges and a debated thumb make a hand
Most people count five digits per hand, built on metacarpal bones and fourteen phalanges—two in the thumb, three in each of the other fingers. Dictionaries disagree whether thumb counts as a finger. Congenital polydactyly or oligodactyly, and amputations, push some hands off the usual five.
Pentadactyly is the default among tetrapods with grasping extremities, and fingertips wear keratin nails. English usage either includes the thumb as digit one or numbers only four fingers starting at the index. Anatomically the thumb sits aside, meeting the trapezium; the palm's five metacarpals each feed a digit. Joints stack as metacarpophalangeal at the base, proximal interphalangeal in the middle, and distal interphalangeal near the nail—except the thumb, which lacks a middle phalanx.
Sesamoid bones nest in tendons around palm bases to add leverage and ease pressure; their exact count varies by person. Each finger can flex, extend, abduct, adduct, and circumduct, with flexion the strongest action. Two large muscles drive most finger bending, helped by others, though muscle bellies and tendons may blend so independent motion is partly shared.
That blended hardware is why a simple wave hides complex engineering: short bones, three hinge levels, and variable sesamoids turn a limb tip into a precision tool. When counts change by birth difference or injury, therapy and design alike must rethink what five once took for granted. Robotics and prosthetic design keep rediscovering the same lesson: independent digits look simple until you try to rebuild the joint stack, tendon routing, and partial muscle blending in hardware. Even a child's pointing gesture recruits that whole chain, which is why hand injuries punch so far above their weight in lost work and lost craft.
Source: Finger
