Palmaris longus muscle substituting for the ring finger slip of flexor digitorum superficialis.

An unusual and unrecorded variation in palmaris longus muscle is described. The muscle had a normal appearance and origin from the common tendon arising from the medial epicondyle of the humerus and from the surrounding intermuscular septa. The distal tendon however entered the hand via the carpal tunnel medial and deep to the median nerve, split and inserted into the lateral and medial sides of the middle phalanx of the ring finger. It therefore substituted completely for the slip to the ring finger from flexor digitorum superficials, which was absent.