HIGH-INCIDENCE OF THE 3RD HEAD OF BICEPS BRACHII IN SOUTH-AFRICAN POPULATIONS

Three different origins were found for the third head of the biceps br achii: (1) an origin from the humeral shaft inferior to and in common with the insertion area for the coracobrachialis; (2) a brachial origi n in which the muscle originated distally from the medial humeral shaf t, adjacent to and in common with the brachialis muscle; (3) a dual or igin in which the medial fibres originated from the short head of bice ps and the lateral fibres from the deltoid fascia and the insertion ar ea of this muscle. In all cases, the third head inserted together with the other 2 heads of biceps brachii into the bicipital aponeurosis an d the radial tuberosity. The third head receives its innervation from the musculocutaneous nerve, as do the other 2 heads of biceps. When th ere is a dual origin, partial innervation from the axillary nerve is p ossible since the fibres of the third head intermingle with those of t he deltoid. There was a 20.5% incidence of the third head in South Afr ican blacks and only an 8.3% incidence in South African whites. Statis tical analysis showed the difference between South African whites and blacks to be significant (P < 0.05). Not all of the blacks, however, h ad a higher incidence, since the Zulus showed a significant absence (P < 0.05) of the third head when compared with the other black populati ons.