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A rare case of four-headed biceps brachii muscle with variation in the course of musculocutaneous nerve was observed in left arm of a 48-year-old embalmed male cadaver. One of the extra head (third) was fleshy throughout, originated from anteromedial surface of shaft of humerus and merged with the deep surface of short head. Fourth thin tendinous head originated just below lesser tuberosity of humerus and joined with the third head. Both accessory heads were lying under cover of short head of biceps. Musculocutaneous nerve was coursing between two supernumerary heads and subsequently between third head and short head of biceps brachii muscle. Origin of third head from shaft of humerus led to passage of nerve between this head and short head, before acquiring normal position between biceps brachii and brachialis muscles, and emerging out as lateral cutaneous nerve of forearm. Intramuscular course of nerve may be a potential site for nerve compression by hypertrophied biceps associated with strenuous regular physical activity of biceps or weight lifting.