Lumbrical muscle

Lumbricals of the hand
The muscles of the left hand. Palmar surface. (1st lumbricalis labeled at bottom right of muscular group.)
Details
Origin	flexor digitorum profundus
Insertion	extensor expansion
Artery	superficial palmar arch, common palmar digital arteries, deep palmar arch, dorsal digital artery
Nerve	3rd and 4th deep branch of ulnar nerve, 1st and 2nd median nerve
Actions	flex metacarpophalangeal joints, extend interphalangeal joints
Identifiers
Latin	musculi lumbricales manus
Dorlands /Elsevier	m_22/12549749
TA	A04.6.02.065
FMA	37385
Anatomical terms of muscle []

The lumbricals are intrinsic muscles of the hand that flex the metacarpophalangeal joints and extend the interphalangeal joints.

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 the extensor expansions.

The first and second lumbricals (the most radial two) are innervated by the median nerve. The third and fourth lumbricals (most ulnar two) are innervated by the deep branch of the ulnar nerve.

This is the usual innervation of the lumbricals (occurring in 60% of individuals). However 1:3 (median:ulnar - 20% of individuals) and 3:1 (median:ulnar - 20% of individuals) also exist. The lumbrical innervation always follows the innervation pattern of the associated muscle unit of flexor digitorum profundus (i.e. if the muscle units supplying the tendon to the middle finger are innervated by the median nerve, the second lumbrical will also be innervated by the median nerve).

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.

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. The lumbricals are used during an upstroke in writing.