a peripheral nerve coming from the brainstem: many animals, including humans, have twelve pairs of such nerves, including the olfactory, optic, trigeminal, facial, and auditory nerves
See cranial nerve in American Heritage Dictionary 4
noun
Any of several nerves that arise in pairs from the brain stem and reach the periphery through openings in the skull. There are 12 such pairs in mammals, birds, and reptiles and usually 10 pairs in amphibians and fish.