A nerve that arises by two sets of roots: the cranial set, arising from the side of the medulla, and the spinal set, arising from the ventrolateral part of the first five cervical segments of the spinal cord. These two roots form the accessory nerve trunk, which divides into two branches: the internal, which unites with the vagus nerve in the jugular foramen and supplies the muscles of the pharynx, larynx, and soft palate; and the external, which continues through the jugular foramen to supply the sternocleidomastoid and trapezius muscles. Also called eleventh cranial nerve.