Which muscle forms the large superficial muscle mass of the upper back and neck?

• A. Deltoid
• B. Latissimus dorsi
• C. Trapezius
• D. Rhomboid major

Answer: (C)

The muscle forming the large superficial muscle mass of the upper back and neck is the trapezius. This broad, flat muscle covers the back of the neck and the upper spine, creating that prominent mass you can feel on the upper back. It attaches from the skull and cervical and upper thoracic vertebrae to the clavicle, the acromion, and the spine of the scapula, and its fibers are organized into regions that help with different motions. Functionally, it elevates the shoulders and upwardly rotates the scapula, retracts the scapula, and assists in extending the neck. It’s innervated mainly by the spinal accessory nerve (with some sensory input from C3–C4).

The other muscles don’t form that large superficial back mass: the deltoid sits as the rounded shoulder cap, not the back mass; the latissimus dorsi is a large muscle of the lower back and flank region; and the rhomboid major lies deeper under the trapezius and is smaller, primarily retracting the scapula rather than forming the large upper back sheet.