The scapula, or shoulder blade, is a large, flat triangular bone that sits at the back of the shoulder. The three muscles that make up the scapula are the trapezius, latissimus dorsi, and pectoralis major. These muscles work together to move the arm and stabilize the shoulder joint.
The trapezius is the largest of the three muscles and extends from the base of the neck to the lower back. It is responsible for moving the scapula up, down, and sideways.
The latissimus dorsi is a large muscle that extends from the lower back to the upper arm. It helps to move the arm backward and downward.
The pectoralis major is a broad muscle that covers much of the chest.
