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a. Clavicular and sternal heads.
Origin: (proximal attachments)
a. Clavicular head: medial half of the clavicle.
b. Sternal head: sternum, upper costal cartilages (1-6), and the aponeurosis of the external oblique.
Insertion: (distal attachments)
a. Lateral lip of the intertubercular (bicipital) groove of the humerus.
b. Crest of the greater tubercle of the humerus.
Both heads working together:
the arm at the shoulder joint.
Nerves & Nerve Roots:
a. Lateral pectoral nerve to the clavicular head (and possible cross innervation by the medial pectoral nerve).
b. Medial pectoral nerve to the sternal head (and possible cross innervation by the lateral pectoral nerve).
a. C5, C6, C7 (for the lateral pectoral nerve).
b. C8 and T1 (for the medial pectoral nerve).