part of cranial nerve formation accessory nerve morphogenesis accessory nerve formation GO:0021608 The process that gives rise to the accessory nerve. This process pertains to the initial formation of a structure from unspecified parts. The spinal branch of this motor nerve innervates the trapezius and the sternocleidomastoid muscles. The cranial branch joins the vagus nerve and innervates the same targets as the vagus nerve. biological_process CN XI biosynthesis CN XI formation