Muscle · Hand

Adductor pollicis

Musculus adductor pollicis

A large flat two-headed muscle deep in the palm, filling the web between the thumb and the index finger. One head is a fan spreading from the middle of the palm, the other a slip from the wrist bones and the bases of two metacarpals; both converge on the ulnar side of the thumb's first phalanx. It pulls the thumb hard across the palm toward the fingers, which is the movement behind every forceful pinch. Despite sitting at the base of the thumb it is not a thenar muscle: the thenar group is supplied by the median nerve, and this one takes the deep branch of the ulnar — which is why a hand can lose its pinch strength while the pad of the thumb still works.