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Pectoralis major

The pectoralis major (Latin: musculus pectoralis major) is a thick, fan-shaped muscle, situated at the chest of the human body. The pectoralis major muscle has three parts:

  • Clavicular part 
  • Sternocostal part
  • Abdominal part

Origin:

The clavicular part originates from the anterior surface of the medial half of the clavicle.

The Sternocostal part originates from the anterior surface of the sternum, as well as from the six costal cartilages

The Abdominal part originates from the anterior layer of the rectus abdominis sheath (m. rectus abdominis sheath)

Insertion

Greater tubercle of the humerus/Lateral lip of the bicipital groove of the humerus(anteromedial proximal humerus)

Action

Adduction and anteversion of the shoulder, medial rotation of the arm, retroversion of the arm. 

The antagonist muscle of the pectoralis major muscle is the Deltoid muscle.

Innervation

The Pectoralis Major muscle is innervated by the lateral and medial pectoral nerves which are the branches of the brachial plexus. The Clavicular head innervation arises from the spinal segments of C5 and C6, but the Sternocostal head innervation arises from C7, C8 and T1