Palmaris longus muscle

The palmaris longus muscle is a superficial flexor of the forearm, notable for its significant anatomical variability.

Origin

It typically originates from the medial epicondyle of the humerus via the common flexor tendon, a shared attachment point with muscles like the pronator teres and flexor carpi radialis.

Insertion

The muscle features a slender, fusiform belly that transitions into a long, thin tendon. This tendon passes superficial to the flexor retinaculum and inserts primarily into the palmar aponeurosis, with some fibers also blending with and inserting directly into the flexor retinaculum (transverse carpal ligament).

Innervation

Innervation is via the median nerve.

Actions

The primary function of the palmaris longus muscle is to tense the palmar aponeurosis and assist in wrist flexion. However, it is generally considered functionally vestigial in humans.

Anatomical variations

Anatomical variations are common for this muscle. It may be absent unilaterally or bilaterally in up to 20% of individuals. Its tendon can also display variations such as bifurcation or trifurcation, and it may give rise to accessory muscles like the palmaris profundus.