Bilateral accessory flexor muscle of the forearm giving rise to a variant head of the first lumbrical

Introduction Accessory flexor muscles in the forearm were first reported by Gantzer in 1813 [1]. These small accessory muscles typically arise from the medial arm and forearm [2] and the deep surface of the flexor digitorum superficialis [3]. Gantzer muscles insert via thin tendons into the tendon of the flexor pollicis longus, digitorum superficialis, or flexor digitorum profundus [2–4]. Here, we report a bilateral accessory deep flexor in the forearm that originated from the lateral side of the forearm and the tendon bifurcated distally into two branches, one of which was associated with a variant head of the first lumbrical muscle. To our knowledge, this bilateral anatomic variation has not been reported previously.