[TA] muscle of superficial layer of anterior (flexor) compartment of forearm; origin, medial epicondyle of humerus; insertion, flexor retinaculum of wrist and palmar fascia; action, tenses palmar fascia and flexes the hand and forearm; is absent about 20% of the time; when tensed, its tendon stands out sharply at the wrist and overlies the median nerve; nerve supply, median. SYN: musculus palmaris longus [TA], long palmar muscle.