The palmaris longus muscle is one of the most variable muscles in the human body. We describe an unusual duplication of this muscle that was found in a female cadaver in the course of a medical school anatomy dissection. The typical palmaris longus, which originates from the medial epicondyle of the humerus and inserts on the palmar apnoneurosis, was replaced by a main muscle that passed deep to the flexor retinaculum, and inserted onto the head of the second metacarpal and an accessory muscle that originated from the distal radius and inserted into the palmar aponeurosis. This variant of the muscle was found bilaterally. An understanding of the variations in the palmaris longus muscle is important, as tendinous portions passing deep to flexor retinaculum can cause median nerve compression and the muscle is often utilized for tendon transfers.
