Pectoralis Major Muscle Beneath the Skin

Description

Prominently highlighted beneath the anterior thoracic skin, the pectoralis major forms a broad, fan-shaped sheet spanning from the medial clavicle and anterior sternum to the upper costal cartilages, its fibers converging laterally toward the proximal humerus. The clavicular head sits superior and slightly anterior to the sternocostal head, with the two portions blending as they course laterally toward the anterior axillary fold. Surrounding musculature in muted tones frames the region, including the sternocleidomastoid superiorly, the deltoid laterally, and the biceps brachii and brachialis on the anterior arm. Clear fiber direction. Understanding the split between clavicular and sternocostal fibers matters when teaching shoulder mechanics and when correlating exam findings to injury patterns, because each portion contributes differently to flexion, horizontal adduction, and internal rotation at the glenohumeral joint. This is also a practical view for reconstructive and oncologic planning: the pectoralis major myocutaneous flap relies on the thoracoacromial artery, and the muscle’s humeral insertion and lateral border define surgical planes during mastectomy and axillary dissection. Anterior contouring is also where you appreciate the relationship between the muscle belly and the anterior axillary fold in pectoralis major rupture, where a torn tendon can leave a visible step-off near the proximal humerus. Use this asset in gross anatomy and kinesiology modules to demonstrate regional anatomy of the chest and shoulder, or in surgical atlases discussing mastectomy approaches, flap design, and pectoral tendon repair. It also supports patient-facing education on chest wall strains and tendon ruptures without exposing deeper neurovascular detail. Anatomical accuracy verified by SciePro's Medical Advisory Board.