Abstract
This article reviews evidence that the major components of the limbic system are present in the major lineages of jawed vertebrates, although divergent influences may make them difficult to recognize. The mammalian hippocampus and each of the major subdivisions of the amygdala have a unique set of topological, connectional, neurochemical, and genetic characteristics. Neuronal groups expressing similar characteristics are present in the forebrains of reptiles, birds, amphibians, teleosts, and primitive ray-finned fish, suggesting that they are homologous, regardless of differences in size and various movements away from their ventricular origins.