Which of the following is not an action of the scapula?

The action of the scapula primarily involves movements that help facilitate shoulder motion and stability. Protraction, upward rotation, and elevation are all recognized movements of the scapula that contribute to the dynamic range of motion for the shoulder girdle.

Protraction refers to the movement of the scapula away from the spine, which allows for better reach in various activities. Upward rotation is essential for raising the arm above the head, as it enables the glenoid cavity to move in a way that aligns with the humerus. Elevation describes the upward movement of the scapula, as seen when shrugging the shoulders.

Supination, however, is not an action associated with the scapula. Instead, supination pertains specifically to the forearm's movement, referring to the rotation of the forearm that turns the palm upward. This differentiation highlights that while the scapula plays a critical role in shoulder motion, it does not participate in actions associated with the forearm and wrist, such as supination. Thus, the correct answer identifies a movement that is unrelated to the functions of the scapula itself.