Pectoralis major is an important adductor and rotator of the shoulder joint. It is attached medially to:
- The medial part of the clavicle
- The length of the anterior sternum
- The costal cartilages of ribs 1 - 7
- The external oblique aponeurosis
The muscle covers the anterior chest wall medially and flattens to a 5 cm long tendon which inserts into the proximal anterior humerus. It is deep to the breast and skin; pectoralis minor and serratus anterior lie deep to it, as does the chest wall. The pectoralis major forms the majority of the anterior border of the axilla.
The pectoralis minor is much smaller, and arises from the anterior ends of the 3rd to 5th ribs, beneath pectoralis major. It passes anteriorly and laterally, becoming much thinner, to insert into the coracoid process of the scapula. The pectoralis minor is an important landmark within the axilla, dividing many structures into three parts.
Lattisimus dorsi arises from a large area; the spines of T7 - T12, the thoracolumbar fascia and the posterior part of the iliac spine. It passes superior and lateral, beneath the inferior angle of the scapula, and passes beneath teres major to form the posterior wall of the axilla. It inserts into the humerus, just medial to the insertion of pectoralis major. It is deep to the skin of the back. It is anterior to teres major in the axilla, and overlain by the subscapularis muscle.