Upper back muscles
Click image to enlarge
These are located on the upper back. They hold and rotate the shoulders and also move the head backwards and sideways. They also pull the arm back to the side after it has been pulled across the chest (shoulder horizontal extension). The trapezius is the most superficial muscle of the back.
This is located on the back of the upper arm. It straightens the arm at the elbow (elbow extension) and also helps to move the arm.
This is a large sheet-like muscle located in the outer portion of the lower and middle back. It pulls the arm down at the shoulders (shoulder adduction), and draws it behind the back (shoulder extension).
Teres major (under lats)
This is a thick, rounded muscle which is located inferior (below) to the teres minor. It helps to form the posterior wall of the axilla (arm pit) (along with the latissimus dorsi and subscapularis). It is often called the ‘little lats’ as it serves the same functions.
Click to enlarge