A case of an accessory brachialis muscle.

Functionally, the brachialis muscle serves a critical role as the primary flexor of the arm at the elbow. However, few reports exist in the literature, which describe variations of this muscle. We present a case of an accessory brachialis muscle (AcBr), found during routine dissection at Harvard Medical School during 2003. The AcBr originated medially from the mid-shaft of the humerus and the medial intermuscular septum. During its course medially, toward the elbow, the AcBr crossed both the brachial artery and the median nerve. The distal tendon split to surround the median nerve before inserting into the common tendon of the antebrachial flexor compartment muscles. Embryological origins and clinical considerations including median nerve entrapment are considered.