Overview of the History of the Cranial Nerves: From Galen to the 21st Century.

Throughout history the description and classification of the cranial nerves has been linked to the development and characteristics of anatomy and the role that it played as a tool in providing rationality to medicine, together with social, cultural, religious, and philosophical factors. Anatomists were interested in the cranial nerves, but they disagreed on their number and their paths. We can divide the history of the cranial nerves into three different periods: the first, early or macroscopic period; the second or microscopic period; and the third period or ontogenesis and genoarchitecture. The main aim of this article is to show how the description and knowledge of the cranial nerves were developed in the course of these three periods, and to highlight the main changes produced and the factors related to these changes. We describe how the first period was mainly focused on establishing the definition, number and paths of the cranial nerves, through contributions ranging from Galen's studies in the second century to Sömmerring's Doctoral Dissertation in 1778 that described 12 cranial nerves for the first time. Then, the microscopic period was concentrated on the identification of the real nuclei of origin of the different cranial nerves located in the brain stem. Finally came the third period, or ontogenesis and genoarchitecture of the rhombecephalic and mesencephalic cranial nerve nuclei. Anat Rec, 302:381-393, 2019. © 2018 Wiley Periodicals, Inc.