Clavicular head: anterior border 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.
Lateral lip of the bicipital groove of the humerus (anteromedial proximal humerus).
The bicipital groove lodges the long tendon of the biceps brachii between the tendons of the pectoralis major on the lateral lip and the those of the teres major on the medial lip. Wiki
Adducts humerus; pulls arm across chest, medial rotation of arm.
Clavicular head: flexes the humerus. Sternocostal head: extends the humerus. As a whole, adducts and medially rotates the humerus. It also draws the scapula anteriorly and inferiorly.
Innervation – Nerve control
Lateral pectoral nerve and medial pectoral nerve.
Clavicular head: C5 and C6.
Sternocostal head: C7, C8 and T1.
Pectoral branch of the thoracoacromial trunk.
The pectoral branch goes back and forth between the two pectoral muscles. Healthline
Pictures of muscles
Trigger Point Referrals