A history of the enumeration of the cranial nerves by European and British anatomists from the time of Galen to 1895, with comments on nomenclature

The enumerations of the modern 12 pairs of cranial nerves by a number of anatomists are reviewed in a continuous historical perspective using original texts and modern translations. The history of the numeration of the nerves is traced from Galen's classification into seven pairs (second century A.D.), through to Willis' nine pairs (1664) and Soemmerring's 12 pairs (1778). Authors describing individual structures (e.g., trochlear and olfactory nerves) for the first time are particularly noted. The contributions made by medieval anatomists such as Achillini, Berengario da Carpi, and Massa are emphasized, as also are the political and religious constraints placed upon the practical activities of anatomists up until the 16th century. It is shown that although the classification of the nerves into 12 pairs was accepted after 1778 by European authors, British texts continued to classify them as nine pairs until the end of the 19th century.