Origin Clavicular head: anterior surface of medial half of clavicle; Sternocostal head: anterior surface of sternum, superior six costal cartilages, and aponeurosis of external oblique muscle Insertion Lateral lip of intertubercular groove of humerus Action Adducts and medially rotates humerus; draws scapula anteriorly and inferiorly; Acting alone: clavicular head flexes humerus and sternocostal head extends it Innervation Lateral and medial pectoral nerves; clavicular head (C5 and C6, sternocostal head (C7, C8, and T1) (C5, C6, C7, C8, T1) Arterial Supply pectoral branch of the thoracoacromial trunk
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