Shoulder and back anatomy. Artwork of the muscles and bones of a human shoulder and upper back in a posterior (rear) view. The muscles shown here include the posterior portion of the deltoid muscle, the triceps of the upper arm, the infraspinatus and teres major muscles of the shoulder (covering the scapula), and the trapezius and latissimus dorsi muscles of the back. The bones include the humerus (upper arm bone), the ribs, and the scapular spine, the upper edge of the scapula (shoulder blade, at top).