The palmaris longus muscle is one of 4 muscles within the superficial layer of the anterior compartment of the forearm, and is responsible for flexion at the wrist joint. It is slender and spindle shaped with a long tendon which passes into the hand attaching to the flexor retinaculum and palmar aponeurosis.

The other muscles in this layer are the flexor carpi ulnaris, flexor carpi radialis and pronator teres. It is located between the flexor carpi radialis and the flexor carpi ulnaris.

The muscles of the superficial layer share a common origin from the medial epicondyle of the humerus.

The palmaris longus is absent in about 15% of the population.