In higher vertebrates, such as reptiles, birds and mammals, there are 12 pairs of cranial nerves. Lower vertebrates, such as fish and amphibians, have 10 pairs of cranial nerves.
In vertebrates, cranial nerves are any paired nerves of the peripheral nervous system that connect the muscles and sense organs of the head and thoracic region directly to the brain. Cranial nerves are comprised of motor neurons and/or sensory neurons. The 12 cranial nerves are olfactory, optic, oculomotor, trochlear, trigeminal, abducent, facial, vestibulocochlear, glossopharyngeal, vagus, accessory and hypoglossal. The vagus nerve is one of the most important nerves because it extends to many of the organs in the upper abdomen and chest.