Three cases of the musculocutaneous nerve not perforating the coracobrachialis muscle.

We encountered three anomalies in which the musculocutaneous nerve did not penetrate the coracobrachialis during a gross anatomy course in 1996. Two of the anomalies were present in the bilateral arms of the cadaver of an 89-year-old woman, and the other in the right arm of the cadaver of a 64-year-old man. In all of the anomlies the musculocutaneous nerve, the lateral cord of the brachial plexus, and the median nerve were contained in a common sheath of connective tissue. Thus, muscular branches to the flexor muscles of the upper arm and the lateral antebrachial cutaneous nerve seemed to arise from the cord and the median nerve. After the common sheath was removed, the musculocutaneous and median nerves were completely separated, or the fusion between the musculocutaneous and median nerves only remained partially. These variations are apparently not rare, and it is possible that the combined paralysis of the musculocutaneous and median nerves would occur. The present variation may be important to clinicians.