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This case report documents a variation in the insertion of the coracobrachialis muscle of the right arm of an adult male cadaver of unknown age. In addition to the normal insertion of the coracobrachialis muscle into the middle of the medial border of the humerus, an additional slender tendon passed inferiorly, crossing anterior to the median nerve and brachial artery before attaching to the medial epicondyle of the humerus. Most of the proximal part of the tendon gave rise to an aponeurotic expansion that inserted into the distal medial border of the humerus. The tendinous insertion and aponeurotic expansion may represent a variant of the coracobrachialis longus (Wood's) muscle and the internal brachial ligament, respectively. The median nerve and brachial artery traversed a tunnel bounded by the additional tendon and aponeurotic expansion as well as the usual humeral insertion of the coracobrachialis muscle. The clinical implication of this variation is that it may be a cause of median nerve entrapment and brachial artery compression.

Reports that describe the abnormalities and complexities of the anatomy of the arm are important with regard to surgical approaches. This case study reports a combined abnormal form of the coracobrachialis and biceps brachii muscles of the left arm of an adult male cadaver that was detected during the educational gross anatomy dissections of embalmed cadavers. The coracobrachialis muscle demonstrated two bellies which formed shortly inferior to its origin from the coracoid process of the scapula. One belly inserted into the middle of the antero-medial surface of the humerus, whereas the other belly inserted into the medial head of the triceps brachii muscle. The musculocutaneous nerve passed between the two bellies, giving a separate branch to each. We suggest that the two bellies of the coracobrachialis muscle may represent the incompletely fused short heads of the ancestral muscle. The biceps brachii muscle showed a third head, which originated mainly from the antero-medial surface of the humerus and partially from an aponeurosis belonging to the medial head of the triceps brachii muscle. These observations were confined to the left upper limb and were not accompanied by any other abnormality.