Final answer:
The middle trapezius is part of the trapezius muscle on the back, the latissimus dorsi is a large back muscle that extends to the sides and arm, and the rhomboids are under the trapezius and help retract the scapula.
Step-by-step explanation:
The middle trapezius is part of the larger trapezius muscle that is located on the back, extending from the occipital bone to the lower thoracic vertebrae and laterally to the spine of the scapula. Its role is to retract the scapula and help in shoulder and neck movements.
The latissimus dorsi is a large, flat muscle on the back that stretches to the sides, behind the arm, and is partially covered by the trapezius on the back near the midline. This muscle is involved in the internal rotation, extension, and adduction of the shoulder joint.
The rhomboids are found beneath the trapezius and consist of the rhomboid major and rhomboid minor muscles. They connect the medial border of the scapula with the vertebrae of the spinal column and aid in retracting the scapula, moving it towards the spinal column.