The structure indicated is the first lumbrical
muscle of the hand.
belong to the intrinsic
group of muscles which act on the hand. The intrinsic muscles include the following muscles/groups:
- Thenar group (act on thumb)
- Hypothenar group (act on little finger)
- Adductor pollicis
- Interossesus muscles
- Palmaris brevis
All the intrinsic muscles of the hand, except the thenar muscles and the lateral two lumbrical muscles are innervated by the deep branch of the ulnar nerve
. The thenar muscles and the lateral two lumbrical muscles are innervated by the median nerve
. A useful mnemonic for remembering this is MEATLOAF. “M
EAT” refers to the M
edian nerve, and LOAF
refers to the muscles which it innervates: L
ateral two lumbricals, O
pponens pollicis, A
bductor pollicis brevis, F
lexor pollicis brevis.
There are 4 lumbrical muscles
which originate from the tendon of the flexor digitorum profundus
muscle. The lateral lumbricals
, whereas the medial lumbricals
. The tendon of the lumbricals pass dorsally to insert onto the extensor expansions
associated with the tendons of the extensor digitorum
muscle. Because of the unique structure of the extensor expansions, the lumbrical muscles act to flex at the metacarpophalangeal
joint, and extend at the interphalangeal
Origin: Tendons of flexor digitorum profundus
Insertion: Extensor expansions of digits 2-5
Action: Flexion of metacarpophalangeal joints. Extension of interphalangeal joint
Innervation: Lateral two lumbricals: median nerve. Medial two lumbricals: deep branch of ulnar nerve.
Learn more about the anatomy of the hand muscles
in this tutorial.