the tenth cranial nerve, a mixed nerve with both sensory and motor fibers that serves many functions. The sensory fibers innervate the external ear, vocal organs, and thoracic and abdominal viscera. The motor nerves innervate the tongue, vocal organs, and—through many ganglia of the parasympathetic nervous system—the thoracic and abdominal viscera. Also called cranial nerve X; pneumogastric nerve.