The pectoralis major attaches to the upper bone of the arm, called the humerus, and is divided into two parts. The clavicular head makes up the upper part, and the sternal head makes up the lower part.
The muscle fibers of the pectoralis end in a flat tendon, which is inserted into a groove called the intertubercular sulcus, in the upper humerus located in the upper arm.
The pectoralis major controls various actions to move the shoulder joint:
- Clavicular head flexes the humerus, as in throwing an underhand ball
- Sternocostal head adducts the humerus, as when flapping the arms
- Pectoralis major medially rotates the humerus, as when arm wrestling
- Pectoralis major keeps the arm attached to the trunk
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