Shoulder and back muscles. Artwork of the muscles 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, and the trapezius and latissimus dorsi muscles of the back. At top (white area) is the scapular spine, the upper edge of the scapula (shoulder blade).