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.