A bone of a digit, (finger or toe). The plural of phalanx is phalanges. Humans have two phalanges in each thumb and big toe; the remaining fingers and toes all have three phalanges. The synovial joints between phalanges of a digit (interphalangeal) and the phalanges and metacarpals are the knuckles. The phalanges are named according to their digit and position: proximal (closest to the body), middle, and distal (closest to the fingertip or toetip). A number is added to indicate which digit a phalanx is located: in humans, the thumb or big toe is I and the last is V.
Phalanx bones are named after the military phalanx, which is a tight formation of infantry in regular rows and files.