Pectoralis major

The pectoralis major (Latin: musculus pectoralis major) is a paired thick, fan-shaped thoracic wall muscle that provides movements of the upper limb. It is the most superficial muscle in the pectoral region, and it covers the anterior surface of the thorax, stretching between the shoulder and sternum. The pectoralis major has three parts - clavicular, sternocostal and abdominal. Each part has its own origin site. In the lateral direction, they all merge and share a common insertion site.

Origin

The clavicular part of the pectoralis major muscle originates from the anterior surface of the medial half (sternal end) of the clavicle. The sternocostal part originates from the anterior surface of the sternum, as well as from the upper six costal cartilages. The abdominal part originates from the anterior layer of the rectus abdominis muscle sheath.

Insertion

As written above, all three parts merge and insert on the crest of the greater tubercle of the humerus.

Action

All parts of the pectoralis major muscle provide adduction and medial (internal) rotation of the arm. The clavicular part provides flexion of the arm, while the sternocostal part is responsible for the arm extension. The pectoralis major is also one of the accessory muscles of the inspiration.

Innervation

The pectoralis major is innervated by the lateral and medial pectoral nerves - branches of the brachial plexus. The lateral pectoral nerve arises from the fifth, sixth and seventh cervical (C5 - C7) nerve roots, while the medial pectoral nerve from the eighth cervical (C8) and first thoracic (T1) nerve roots.

Blood supply

The pectoralis major muscle receives arterial blood supply from the branches of the thoracoacromial and internal thoracic arteries.