Upper limb

Third Lumbrical

Musculus lumbricalis III manus

Origin

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

Insertion

Radial side of the extensor hood and proximal phalanx of the ring finger

Function

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

Innervation

Ulnar nerve, deep (motor) branch

Movement & chain

Unlike the first and second lumbricals, which are innervated via the ulnar nerve, this enables the combined MCP flexion/IP extension of the ring finger, essential for fine grip movements.

Palpation

Deep in the midpalmar space between ring and middle finger flexor tendons; not individually palpable.

Clinical

Bipennate muscle innervated by the deep branch of the ulnar nerve; denervation produces clawing of the ring finger.

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