Clavicular head: flexes the humerus. Sternocostal head: Adducts the humerus. As a whole, adducts and medially rotates the humerus. It also draws the scapula anteriorly and inferiorly.
Innervation
lateral pectoral nerve and medial pectoral nerve, Clavicular head: C5 and C6, Sternocostal head: C7, C8 and T1
Udspring
Clavicular head: anterior surface of the medial half of the clavicle. Sternocostal head: anterior surface of the sternum, the superior six costal cartilages, and the aponeurosis of the external oblique muscle