Cranial nerves arise from the brain and [[Hindbrain - Anatomy & Physiology|brain stem]], rather than the spinal cord. Nerves arising from the spinal cord are the [[PNS Structure - Anatomy & Physiology|peripheral nerves]]. There are 12 pairs of cranial nerves and these pairs of nerves passage through [[Skull and Facial Muscles - Anatomy & Physiology|foramina in the skull]], either individually or in groups. Cranial nerves are traditionally referred to by Roman numerals and these numerals begin cranially and run caudally.