Upper limb
Pectoralis Major
Musculus pectoralis major
- Origin
- Medial half of the clavicle (clavicular head), sternum and costal cartilage of ribs 2-6 (sternocostal head), and aponeurosis of the external oblique abdominis (abdominal head)
- Insertion
- Crest of the greater tubercle of the humerus (lateral lip of the intertubercular sulcus)
- Function
- Adduction and internal rotation of the arm; the clavicular head flexes the arm, the sternocostal head is the primary depressor when the arm is raised
- Innervation
- Medial and lateral pectoral nerves (C5-T1)
- Movement & chain
- With a fixed arm, the fibers act as an accessory muscle of respiration by pulling the ribs upward; functionally crucial in pushing and throwing movements and in pulling the body upward (e.g. climbing)
- Palpation
- Easily seen and felt as the anterior axillary fold; the clavicular and sternocostal heads can be distinguished separately by resisting flexion and adduction respectively
- Clinical
- A tear or avulsion of the tendon at the humerus occurs in strength athletes (bench press); shortening contributes to a protracted shoulder posture
- Segmental innervation
- Myotome C5-T1 (clavicular head mainly C5-C6, sternocostal head C7-T1).
- In clinical practice
- The anterior axillary fold, formed by this muscle, is a landmark for locating the axillary lymph node stations during breast examination
- Region in the model
- Upper limb