Abnormal morphology of the musculature of the neck Any structural anomaly of the neck region Any structural anomaly of the trapezius muscle, the large superficial back muscle that resembles a trapezoid. It extends from the external protuberance of the occipital bone to the lower thoracic vertebrae and laterally to the spine of the scapula. The trapezius has upper, middle, and lower groups of fibers. The ventral rami of C3 and C4 innervate the sensory functions of the trapezius. The spinal accessory nerve (cranial nerve XI) innervates the motor function of the trapezius. The function of the trapezius is to stabilize and move the scapula.