Bilateral aberrant biceps brachii muscles with special reference to their common nerve trunks.

Aberrant biceps brachii muscles (BB); the right aberrant head, the left aberrant head, and the left aberrant bundle, were observed bilaterally in a 94-year-old Japanese female cadaver during a regional anatomy of the upper extremities. We examined the nerve supply as well as scrutinizing these aberrant BB. The branches to the right aberrant head and the right brachialis muscle arose as a common nerve trunk from the musculocutaneous nerve, and both branches entered each muscle from the ventral aspect. The branches to the superior portion of the left aberrant bundle and the short head of the BB arose as a common nerve trunk from the musculocutaneous nerve, and both branches entered each muscle from the dorsal aspect. The branches to the inferior portion of the left aberrant bundle and the left aberrant head arose separately from the musculocutaneous nerve, but they were found to be closely related after peeling off the epineurium. From these observations, we speculated that the right aberrant head could have differentiated from the brachialis muscle, the left aberrant head from the long head of the BB, and the left aberrant bundle aberrant head from the short and long head of the BB, based on the formation of the common nerve trunk and the close relation of the nerve fibers. Our suggested muscular differentiation agreed with the entering aspect (ventral/dorsal aspect) of the innervating nerve.