The split flexor digitorum superficialis.

Variations of the muscles of the anterior forearm are common. We report the cadaveric findings of an unusual variant of flexor digitorum superficialis (FDS). The deep part of the FDS was found to be split and showed two distinct fusiform muscle bellies. The medial belly originated from the common flexor tendon from the medial condyle of the humerus and continued as a thin tendon at the middle of the forearm to insert onto the fifth digit. The lateral belly blended proximally with the deep surface of the superficial portion of the FDS and ended in a relatively thicker tendon, which was inserted onto the second digit. The median nerve passed between the medial and lateral bellies of the deep part of the FDS. To our knowledge, this is only the second report of a split FDS in the extant literature. A review of neuromuscular variations of the anterior forearm is presented.