Since their description by Sömmering in 1778, the cranial nerves have been grouped into twelve pairs, to which a 13th pair, the nervus terminalis, was added 100 years later by Fritsch in 1878 (cited in Haller von Hallerstein 1934). The central pathway character of the first and second pair was soon recognized and that of the 13th pair is still a subject of debate with respect to whether it is an independent cranial nerve or part of the olfactoretinal system (Szabo 1991). In the present endeavor we confine the discussion to the efferent nuclei of the “real” cranial nerves which emerge from the brain stem. As the classification of these nerves and nuclei is strongly associated with the various “head theories,” we start with a brief survey of them.
KeywordsCranial Nerve Branchial Arch Trunk Region Preganglionic Neuron Lateral Plate Mesoderm
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