Pectoralis Major Muscles

Description

Across the anterior thoracic wall, the paired pectoralis major muscles dominate the chest as broad, fan-shaped sheets with a wide medial origin and a narrow lateral convergence onto the proximal humerus. Superior fibers arising from the clavicle lie anterior to the upper thorax and run inferolaterally, while the sternal and costal fascicles sweep laterally with a more horizontal to superolateral course toward the anterior axillary fold. Lateral to the sternum, the right and left bellies frame the midline and sit inferior to the clavicles and medial to the deltoid contours at the shoulder. Fiber direction is the teaching point in this anterior view, because the clavicular and sternocostal heads contribute differently to shoulder motion and to clinical examination of the chest and axilla. Contraction draws the humerus into adduction and medial rotation, and the clavicular head assists flexion while the lower sternocostal fibers can act from a flexed position to extend the arm back toward anatomical position. A clear depiction of the anterior axillary fold also supports surgical and sports-medicine discussions, since the pectoralis major tendon is a known site of rupture during heavy eccentric loading (classically the bench press), with retraction producing a visible deformity of the chest contour and axillary fold. Use this asset in gross anatomy and kinesiology teaching to explain fascicle orientation and functional compartmentalization, and in orthopedics or radiology content to orient readers before discussing MRI findings of tendon avulsion at the humeral insertion. It also suits patient-facing education on chest wall injuries and operative repair planning where surface landmarks matter. Anatomical accuracy verified by SciePro's Medical Advisory Board.