arises by two sets of roots: cranial, emerging from the side of the medulla, and spinal, emerging from the ventrolateral part of the first five cervical segments of the spinal cord; these roots unite to form the accessory nerve trunk, which divides into two branches, internal and external; the internal branch, carrying fibers of the cranial root, unites with the vagus in the jugular foramen and supplies the muscles of the pharynx, larynx, and soft palate; the external branch continues independently through the jugular foramen to supply the sternocleidomastoid and trapezius muscles. Syn: nervus accessorius [NA], accessorius willisii, eleventh cranial nerve, spinal accessory nerve.