Definition:

1. nerve that arises by two sets of roots: the presumed cranial, emerging from the side of the medulla, and the presumed 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. Even though the accessory nerve was originally believed to have cranial and spinal roots, it is now the general view that the so-called cranial root is actually a portion of the vagus nerve.nervus accessorius [CN XI], accessorius willisii, eleventh cranial nerve [CN XI], spinal accessory nerve
   Stedman's Medical Dictionary, 28th Edition. 2006 Lippincott Williams & Wilkins