Unique features of the present work include: - Only authorized English translation of the original Spanish text, adhering as much as possible to the letter, with correction of the obvious errors already predicted by Cajal in his Preface. - Added facts appearing in the French version, with correction of old as well as new errors, the latter probably due to inaccuracies in translating into French some nuances of the Spanish language. - Uniform of nomenclature according to contemporary scientific English. - Annotations on Cajal's changing concepts over time, the elucidation of certain structures...

Most scientists agree that the 21st century will be the "Century of Biology." The revolution that started a few decades ago with the extraordinary develop ment of molecular biology, has provided the basis for the understanding of the mechanisms that govern life through the regulation of cell function and cell-to cell interactions. Neuroscience will surely be one of the biological disciplines that will profit the most from this revolution. Neuroscience comprises the study of the brain, and the more difficult relationship of brain and behavior. It is indeed a very broad field of investigation...