Cranial Nerves: Any of the twelve nerves which attach to the brain. They are the olfactory (I), optic (II), oculomotor (III), trochlear (IV), trigeminal (V), abducens (VI), facial (VII), vestibulocochlear (VIII), glassopharyngeal (IX), vagus (X), spinal accessory (XI), and hypoglossal (XII) nerves.