A new approach using comparative neuromorphology is taken in this study dealing with the organization of the efferent nuclei of cranial nerves. The authors use the cobalt labelling technique to identify neuron types and follow their presence, or absence, in different animal species. They suggest a new classification which is free from a number of controversies inherent in the classical classification. The results suggest that evolutionary changes in the center and in the innervated periphary parallel each other with increasingly complex function.

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1 Introduction.- 1.1 Theories Regarding the Evolution of the Head.- 1.2 The Classification of Cranial Nerves.- 1.3 Inconsistencies and Contradictions in the Classification of Cranial Nerves.- 2 Materials and Methods.- 3 The Hypoglossal Nucleus: The Appearance of the Muscular Tongue.- 3.1 Frog.- 3.2 Lizard.- 3.3 Rat.- 3.4 Conclusion.- 4 The Control of Patterned Eye Movements: The Oculomotor, Trochlear, and Abducens Nuclei.- 4.1 The Positions of the Eye Moving Nuclei and the Organization of Muscle Innervation.- 4.2 Neuronal Morphology in the Eye Moving Nuclei.- 4.2.1 Frog.- 4.2.2 Lizard.- 4.2.3 Rat.- 4.3 Conclusion.- 5 The Protection of the Eye: The Accessory Abducens Nucleus.- 5.1 The Position of the Accessory Abducens Nucleus.- 5.2 The Neuronal Morphology in the Accessory Abducens Nucleus.- 5.3 The Function of the Accessorius Abducens-Retractor Bulbi System.- 5.4 Conclusion.- 6 Control of Jaw Movements and Facial Expression: The Trigeminal and Facial Nuclei.- 6.1 The Primary Mandibular Joint and Its Muscles.- 6.2 The Secondary Mandibular Joint and Its Muscles.- 6.3 The Control of Movements at the Primary Mandibular Joint: The Amphibian and Sauropsidian Trigeminal and Facial Nuclei.- 6.3.1 Frog.- 6.3.2 Lizard.- 6.3.3 Bird.- 6.4 The Control of Movement at the Secondary Mandibular Joint: The Mammalian Trigeminal Nucleus.- 6.5 The Control of Facial Expression: The Mammalian Facial Nucleus.- 6.6 Conclusion.- 7 The Muscles of the Middle Ear.- 7.1 The Central Innervation of the Tensor Tympani.- 7.2 The Central Innervation of the Stapedius.- 7.3 Conclusion.- 8 Deglutition and Phonation: The Ambiguus Nucleus.- 8.1 The Innervated Periphery.- 8.2 The Structure and Cytoarchitecture of the Ambiguus Nucleus.- 8.2.1 Frog.- 8.2.2 Lizard.- 8.2.3 Rat.- 8.2.3.1 The Position and Structure of the Ambiguus Nucleus.- 8.2.3.2 Somatotopic Organization of the Ambiguus Nucleus.- 8.3 Conclusion.- 8.3.1 Species Differences.- 8.3.2 Cytoarchitecture of the Ambiguus Nucleus.- 8.3.3 The Relation to the Accessory Nerve Nucleus.- 9 The Control of Head Movements: The Accessory Nerve Nucleus.- 9.1 The Periphery.- 9.2 The Accessory Nerve.- 9.3 The Topography and Cytoarchitecture of the Accessory Nerve Nucleus.- 9.3.1 Frog.- 9.3.2 Lizard.- 9.3.3 Rat.- 9.3.4 Conclusion.- 10 Neurons of the Cranial Parasympathetic Outflow.- 10.1 The Edinger-Westphal Nucleus and Ciliary Ganglion System.- 10.1.1 The Periphery.- 10.1.2 The Central Nucleus.- 10.2 The Medullary Parasympathetic Outflow.- 10.2.1 The Peripheral Targets.- 10.2.2 The Distribution of the Preganglionic Neurons.- 10.2.2.1 Rat.- 10.2.2.2 Lizard.- 10.2.2.3 Frog.- 10.2.3 The Organization of the Medullary Preganglionic Neurons.- 10.3 Conclusion.- 11 General Conclusions.- 11.1 The Arrangement of Cranial Nerve Motor Nuclei.- 11.2 Comments on the Morphological Classification.- 11.3 Trends in the Evolution of Cranial Nerve Nuclei.- 11.4 Corollary Considerations.- 11.5 Summary.- References.