An Anatomical Study on the Third Head of Biceps Brachii in Human.

Background : The supernumerary head of biceps brachii muscle is interesting not only to anatomists but also to the clinicians, from the phylogenetic point of view as well as from the surgical view due to the partial entrapment of either the musculocutaneous or median nerve in some cases. Objective: Was to describe and study a case of a biceps brachii muscle with an additional head. Methods: During the dissection of the anterior region of the arm, a three-headed biceps brachii muscle was observed in the flexor aspect of the left arm of a 60 year old male cadaver. Results: The additional head originated by tendinous fibres from an oblique line running from the proximal and medial to the distal and lateral side, along the middle of the anteromedial surface of the humerus. The insertion of the third head into the common tendon was more closely associated with the short head than the long head. It was inserted into the proximal part of the posterior aspect of the common biceps tendon. This common tendon was inserted into the radial tuberosity of radius. The third head has a vertical orientation situated anterior to brachialis and covered by the two conjoined heads (short and long) of biceps brachii muscle. Length of the third head of biceps brachii muscle was 12 mm, width and thickness close to its origin was 6 mm and 3 mm respectively. The innervation and arterial supply of the accessory head was from the branches of the median nerve and brachial artery respectively.The long and short heads each provided roughly 40% of total muscle mass, with the long head being slightly heavier, whereas the remaining 20% of the total mass was attributed to the third head. Conclusion:  Based on its innervations and relationships, the third head of biceps is probably derived from the muscles of the anterior compartment of the arm.