This book gives a comprehensive survey of the structure and fiber connections of the brain stem in a well-differentiated lizard, the savanna monitor lizard, Varanus exanthematicus. It comprises a cytoarchitectonic analysis of the cell masses in the brain stem, a discussion of the localization of monoaminergic and certain peptidergic neuron systems and a review of the experimental data currently available on this lizard and on closely related species. The structure of the brain stem is discussed in terms of functional systems; wherever possible, the cell masses are treated in the framework of their interconnecting fiber paths as demonstrated by tract-tracing techniques and in relation to experimental data on other reptiles. Furthermore, some comments on the similarities and differences between the reptilian and the mammalian brain stems are presented. Research in "lower" vertebrates, including reptiles, has added much to our knowledge on basic features in the organization of the neuronal circuitry common to vertebrates.