What additional structures are involved in the origin of the pectoralis major muscle?

The pectoralis major muscle primarily originates from two anatomical regions: the sternum and the first to sixth ribs. These structures provide the attachment points that are essential for the function of the muscle, which plays a significant role in movements such as flexion, adduction, and medial rotation of the humerus.

The pectoralis major muscle has a broad origin that allows for a wide range of motion in the shoulder joint. The attachment to the sternum allows the muscle to stabilize the shoulder girdle while the rib attachments enable it to assist with breathing, particularly during exertion. This anatomical setup supports various activities, including pushing and lifting.

In contrast, the other structures listed—such as the lateral and medial epicondyles, the greater tubercle of the humerus, and the medial olecranon process—are not involved in the origin of the pectoralis major. Instead, they are associated with different muscles or functions in the arm and elbow regions. This distinction is crucial for understanding muscle anatomy and their specific roles in movement and stability in the upper body.