How many?

In 2nd century AD, Galen established 7 pairs of cranial nerves in his De Anatomicis Administrationibus. 1500 years later, in the 17th century, Willis identified 9 pairs in his Cerebri anatome. 100 years later, Samuel Sömmerring numbered the twelve cranial nerves in his doctoral dissertation De basi encephali et originibus nervorum cranio egredentium libri quinque. However, Gray’s only picked up the 12 pairs another 100 years later in its 11th edition.

CN Zero

There is a Cranial Nerve Zero. It is also known as nervus terminalis. First identified in shark brains. It’s function is unknown. It is located near the cribriform plate.

The Pathetic Cranial Nerve

This was the last nerve to be identified. For about 200 years, it was known as the nervos oculorum patheticos, or the pathetic nerve of the eye.