1 Introduction.- 2 Materials and Techniques.- 2.1 Cytoarchitectonic Analysis.- 2.2 Immunohistochemical Procedures.- 2.3 Tract-Tracing Studies.- 2.3.1 Anterograde Degeneration Studies.- 2.3.2 Horseradish Peroxidase Retrograde and Anterograde Transport Studies.- 2.3.3 Retrograde Fluorescent Tracer Studies.- 2.3.4 Anterograde [3H] Leucine Tracing Studies.- 3 Gross Anatomy.- 3.1 The Brain Stem.- 3.2 The Cranial Nerves.- 4 Spinal Projections to the Brain Stem.- 4.1 The Dorsal Column Nucleus and its Afferent and Efferent Connections.- 4.2 Fiber Systems Ascending in the Lateral Funiculus.- 4.2.1 The Spinal Lemniscus.- 4.2.1.1 Spinorhombencephalic Projections.- 4.2.1.2 Spinomesencephalic Projections.- 4.2.1.3 Spinothalamic Projections.- 4.2.2 Spinocerebellar Projections.- 5 Organization and Connections of the Sensory Trigeminal Nuclei.- 5.1 Cytoarchitecture.- 5.2 Primary Afferents.- 5.3 Central Trigeminal Projections.- 6 The Solitary Tract and Related Nuclei.- 6.1 Cytoarchitecture : Viscerosensory Nuclei.- 6.2 Primary Afferents.- 6.3 Central Visceral and Taste Pathways.- 7 Cranial Nerve Motor Nuclei.- 7.1 Somatomotor Nuclei.- 7.2 Branchiomotor Nuclei.- 7.3 Visceromotor Nuclei.- 8 The Vestibular Nuclear Complex and Related Structures.- 8.1 Cytoarchitecture.- 8.2 Primary Afferents.- 8.3 Central Vestibular Projections.- 8.3.1 The Fasciculus Longitudinalis Medialis.- 8.3.2 Vestibulospinal Pathways.- 9 Acoustic Projections.- 9.1 Primary Acoustic Projections and Nuclei.- 9.2 The Superior Olive.- 9.3 The Torus Semicircularis.- 10 Visual Input to the Brain Stem.- 10.1 The Tectum Mesencephali.- 10.1.1 Tectal Lamination.- 10.1.2 Tectal Afferents.- 10.1.2.1 Visual Input.- 10.1.2.2 Nonvisual Afferents.- 10.1.3 Tectal Efferents.- 10.1.3.1 Ascending Tectal Efferents.- 10.1.3.2 Descending Tectal Efferents.- 10.2 The Nucleus of the Basal Optic Root.- 10.3 The Isthmic Nuclei.- 11 Forebrain Projections to the Brain Stem.- 11.1 Notes on the Organization of the Reptilian Forebrain.- 11.2 Basal Ganglia Projections to the Brain Stem.- 11.2.1 The Substantia Nigra and Ventral Tegmental Area.- 11.3 Diencephalic Projections to the Brain Stem.- 11.3.1 Thalamic Projections to the Brain Stem.- 11.3.2 Hypothalamic Projections to the Brain Stem.- 11.4 The Habenulointerpeduncular Tract.- 11.4.1 The Nucleus Interpeduncularis.- 12 Cerebellar Connections.- 12.1 Notes on the Cerebellar Cortex.- 12.2 The Cerebellar Nuclei.- 12.3 Afferent Connections of the Cerebellum.- 12.3.1 Spinal Afferents.- 12.3.2 Rhombencephalic Afferents.- 12.3.2.1 Vestibular Afferents.- 12.3.2.2 The Nucleus Prepositus Hypoglossi.- 12.3.2.3 The Inferior Olive.- 12.3.2.4 Other Rhombencephalic Afferents.- 12.3.3 Mesencephalic Afferents.- 12.3.4 Prosencephalic Afferents.- 12.4 Efferent Connections of the Cerebellum.- 12.4.1 Corticonuclear Projections.- 12.4.2 Projections of the Cerebellar Nuclei.- 12.4.3 The Red Nucleus.- 13 The Reticular Formation.- 13.1 Cytoarchitecture.- 13.2 Monoaminergic and Peptidergic Components.- 13.2.1 Distribution of Catecholamine Neurons in the Brain Stem.- 13.2.2 Distribution of Serotonin-Containing Neurons in the Brain Stem.- 13.2.3 Peptidergic Components.- 13.3 Ascending Projections.- 13.3.1 Ascending Projections of the Brain Stem Reticular Formation.- 13.3.2 Ascending Monoaminergic Systems in the Reptilian Reticular Formation.- 13.4 Descending Projections.- 13.4.1 Reticulospinal Projections.- 13.4.2 Descending Monoaminergic Projections to the Spinal Cord.- 13.4.2.1 Raphespinal Projections.- 14 Concluding Remarks.- 14.1 Ascending Projections.- 14.2 Descending Projections to the Brain Stem.- 14.3 Descending Projections from the Brain Stem.- 14.4 Cerebellar Connections.- 14.4.1 Cerebellar Afferents.- 14.4.2 Cerebellar Efferents.- 14.5 Research Perspectives.- Acknowledgments.- References.