Lumbricals of the hand


 * For the foot muscles, see Lumbrical muscle of the foot

The lumbrical muscles are intrinsic muscles in the fingers that allow flexion at the metacarpophalangeal joints, while maintaining extension at the interphalangeal joints.

Structure
There are four of these small, worm-like muscles on each hand. These muscles are unusual in that they do not attach to bone. Instead they attach proximally to the tendons of flexor digitorum profundus and distally to extensor expansions on the dorsal surface (back) of the hand.

Innervation
The first and second lumbricals (i.e. the two that are most lateral) are innervated by the median nerve. The third and fourth lumbricals (i.e. the most medial two) are innervated by the deep branch of the ulnar nerve.

Blood supply
There are four separate sources of blood supply for these muscles: the superficial palmar arch, the common palmar digital artery, the deep palmar arch, and the dorsal digital artery.

Actions
The lumbrical muscles, with the help of the interosseous muscles, simultaneously flex the metacarpophalangeal joints while extending both interphalangeal joints of the digit on which it inserts.

Other lumbricals
There are also lumbrical muscles of the foot that have a similar action, though these are of less clinical concern.