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Pectoralis Muscle: (Musculus pectoralis major)

a. Clavicular head.

b. Sternal head.

Attachments: Origin & Insertion
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.

Clavicular head:
a. Flexes the arm at the shoulder.

Sternal head:
a. Extends the arm at the shoulder from a flexed position.

Both heads working together:
a. Medially rotate the arm at the shoulder.

b. Adduct the arm at the shoulder.

Nerves & Spinal Segments:
Nerves to the muscle:
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).

Nerve roots:
a. C5, C6, C7 (for the lateral pectoral nerve).

b. C8 and T1 (for the medial pectoral nerve).

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Cervical Vertebrae