Muscle · Hand

Lumbricals (hand)

Musculi lumbricales manus

Four slender muscles in the palm with an arrangement found almost nowhere else in the body: instead of starting on bone, they start on the tendons of a muscle in the forearm and end in the fibrous hood over the back of each finger. That wiring lets them do two opposite things at once — bend the fingers at the knuckles while straightening them at the smaller joints beyond. It is the position the hand takes to hold a plate, a book, or a playing card, and it is also thought to make them fine sensors of how hard the long flexors are pulling. The radial two answer to the median nerve and the ulnar two to the ulnar, so this one muscle group sits across the hand's great nerve divide.