Fig. 1. The morphological types of the CBM. (A) Single belly CBM (type I) originating from the CP of scapula in common with the SH with superficial course of MCN. (B) Two-headed CBM (type II) shows superficial head (1) originating from CP and deep head (2) originating from SH with passage of MCN between them. (C) The three-headed CBM (type III) exhibits two superficial heads (1, 2) originating from the SH directly or through a common tendon and a deep head (3) originating from CP and inserts into the middle of anteromedial surface of humerus with passage of MCN between its superficial and deep heads. (D) The four-headed CBM (type IV) has two superficial heads (1, 4) originating from CP and SH respectively and two deep heads (2, 3) originating from CP directly and in common with SH with passage of MCN between the deep and superficial heads. The 4th head (4) fuses with the common tendon of biceps brachii muscle. CBM, coracobrachialis muscle; MCN, musculocutaneous nerve; LH, long head of biceps; LCF, lateral cutaneous nerve of forearm; MN, median nerve; LC, lateral cord of brachial plexus; LR, lateral root of MN; MR, medial root of MN; AX, axillary artery; BA, brachial artery; SH, short head of biceps; UN, ulnar nerve; CP, coracoid process; MC, medial cord; Cb, communicating branch; 3rd, third head of biceps; Lat. Dorsi, latissimus dorsi muscle.
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