pectoralis major muscle

The pectoralis major is a paired, superficial muscle located on the anterior surface of the thoracic cage. If you’re a gym lover, you’ll hear these muscles also being referred to as the pecs muscles. The pectoralis major has a broad origin, based on which it is divided into three parts: clavicular part, sternocostal part and abdominal part. All three parts converge laterally and insert onto the greater tubercle of humerus.
The pectoralis major muscle is a fan-shaped muscle that consists of three parts that originate from three different sites:
The clavicular part originates from the anterior surface of the medial half of the clavicle.
The sternocostal part originates from the anterior surface of sternum and the anterior aspects of the costal cartilages of ribs 1-6.
The smallest, abdominal part originates from the anterior layer of the rectus sheath.
The muscle fibers from all three parts run laterally, converging towards the proximal humerus. They give off a broad tendon that inserts along the crest of the greater tubercle of the humerus.
The pectoralis major muscle is innervated by the lateral and medial pectoral nerves (root value C5-T1), which stem from the brachial plexus.