Unilateral Variation in Biceps Brachii Muscle With Four Heads

Abstract

Biceps brachii is one of the muscles of the anterior compartment of the arm. Normally it has two heads; long head which originates from the supraglenoid tubercle of glenoid cavity and short head from the tip of coracoid process of scapula. During routine Anatomy dissection for first MBBS students, in an adult male cadaver aged approximately 65 years, a biceps brachii muscle with four heads was observed. The short and long heads had their normal origin. In addition to this third head was found to be originating obliquely from the shaft of the humerus along the lateral side of insertion of the coracobrachialis muscle and the fourth head originated from superomedial margin of origin of the brachialis muscle. Both additional heads were directed downwards and laterally and joined the deeper surface of short head. All heads of this variant biceps brachii muscle were supplied by the musculocutaneous nerve. Earlier, Poudel PP and Bhattarai C (2009) reported the presence of 3 rd head in 6.2% and 4 th head also in 6.2% where as Standring (2008) reported the presence of 3 rd head in 10%. Knowledge of the existence of such variations of biceps brachii may be significant in surgeries of the arm in trauma, tumors, etc.