Retraction of scapula is by:

Ans. B. Middle fibres of trapeziusThe trapezius is a large paired surface muscle that extends longitudinally from the occipital bone to the lower thoracic vertebrae of the spine and laterally to the spine of the scapula.The trapezius has three functional parts: The upper fibers elevate the scapulae, the middle fibers retract the scapulae, and the lower fibers depress the scapulae.