Lumbricals of hand

The lumbricals (Latin: musculi lumbricales) are four deep intrinsic muscles of the hand that extend between the metacarpal bones. Together with the dorsal and palmar interossei, the lumbricals belong to the middle muscle group of the hand. The name of these muscles comes from the Latin word lumbricus which means "worm" because the lumbricals have a worm-like appearance. They are unique muscles as their insertion and origin sites are muscle tendons. The lumbricals provide movements of the fingers.

Lumbricals of hand
OriginTendons of flexor digitorum profundus muscle
Insertion Tendons of extensor digitorum muscle
Action

Flexion of proximal phalanges at metacarpophalangeal joints (2nd - 5th)

Extension of middle and distal phalanges at interphalangeal joints (2nd - 5th)

Innervation

Lumbricals I, II - median nerve (C8 - T1)

Lumbricals III, IV - ulnar nerve (C8 - T1)

Blood supply Superficial palmar arch, deep palmar arch, dorsal metacarpal arteries, dorsal digital arteries, common palmar digital arteries

Origin

The lumbricals originate from the tendons of the flexor digitorum profundus muscle.

Insertion

The lumbricals insert on the tendons of the extensor digitorum muscle.

Action

The lumbricals provide the flexion of the proximal phalanges at the second to fifth metacarpophalangeal joints and extension of the middle and distal phalanges at the second to fifth interphalangeal joints.

Innervation

The first and second lumbricals (lumbricals I, II) are innervated by the median nerve (C8 - T1), while the third and fourth (lumbricals III, IV) are innervated by the ulnar nerve (C8 - T1). Both nerves arise from the brachial plexus.

Blood supply

The lumbricals receive arterial blood supply from several arteries. They are supplied by the superficial and deep palmar arches, dorsal metacarpal and dorsal digital arteries and the common palmar digital arteries.