MEDICAL ANIMATION TRANSCRIPT: The shoulder joint is a highly mobile ball-and-socket joint made up of three bones: the humerus, or upper arm, the clavicle, or collar bone, and the scapula, or shoulder blade. The humeral head is the ball-like structure at the top of the humerus. The clavicle runs between the breastbone and the top of the scapula. The scapula is a flat, triangle-shaped bone that forms the back and top of the shoulder. The glenoid cavity, or socket, is a shallow depression in the part of the scapula closest to the arm. The ball of the humeral head fits into this socket. Articular cartilage is a tissue that covers the humeral head and lines the glenoid cavity. It allows the joint to glide smoothly. Four muscles start at the scapula and run toward the shoulder joint. These muscles are attached to the humerus with tendons, which are strong cords of tissue that connect muscles to bone. These tendons form the rotator cuff, which is a capsule that supports the bones of the shoul...