Upper limb

Fourth Lumbrical

Musculus lumbricalis IV manus

Origin

Adjacent sides of the tendons of flexor digitorum profundus to the ring and little fingers (bipennate, no bony attachment)

Insertion

Ulnar side of the extensor hood and proximal phalanx of the little finger

Function

Flexion of the MCP joint with simultaneous extension of the IP joints of the little finger

Innervation

Ulnar nerve, deep (motor) branch

Movement & chain

Enables the combined MCP flexion/IP extension of the little finger, a functional part of the 'writing position' of the fingers in fine motor tasks.

Palpation

Deep adjacent to the 5th digit flexor tendon in the palm; cannot be isolated from surrounding tissue.

Clinical

Innervated by the ulnar nerve; paralysis produces isolated clawing of the little finger (Duchenne's sign of ulnar claw).

Segmental innervation

Ulnar nerve, C8-T1.

In clinical practice

The bony origin shown is an approximation; the actual origin is tendinous in the palm.

Region in the model

Upper limb