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 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.
Medial epicondyle of the humerus (common flexor origin)
Flexion at the wrist