The most frequent supernumerary biceps muscle bellies originated from the humerus at the level of the coracobrachialis insertion, and inserting on the biceps muscle belly, tendon or
bicipital aponeurosis, while other origin and insertions were much less frequent, originating more superior on the humeral head, or laterally from the intermuscular septum.
In terms of the individual regions, the sternocostal head originates on the (1) anterior surface of the sternum, (2) the superior six costal cartilages, and (3)
aponeurosis of the external oblique muscle, and then inserts on the
bicipital groove.