Muscle · Hand

Dorsal interossei (hand)

Musculi interossei dorsales manus

Four two-headed muscles filling the spaces between the bones on the back of the hand. They spread the fingers apart, each pulling its finger away from an imaginary line drawn through the middle finger — the mnemonic is DAB, dorsal abduct. Beyond spreading, they help the lumbricals hold the fingers in the bent-knuckle, straight-finger shape that stabilises a grip. The first one, in the web between thumb and index, is the largest and the most visible muscle in the hand: when the ulnar nerve fails, that web hollows out, and it is often the earliest thing an examiner notices.