Phylogenetic and Ontogenetic Aspects of the Lemniscal Systems and the Pyramidal System

A more comprehensive understanding of encephalization during vertebrate evolution would be uniquely attained if one could compare the actual brains of the ancient common ancestors with those representing a sufficiently complete series of subsequent phyletic stages. Unfortunately, such a panoramic view can never be attained since the former and many of the latter brains are lost in the geological past. Therefore, at present, one can trace the process of the phylogenetic development of the brain only through the evaluation and reconstruction of paleoneurological and comparative neoneurological evidence. The phylogenetic interpretations presented below are made with the full awareness of the pitfalls inherent in evaluating data obtained from living descendents. Often only inferences can be made as to whether apparently similar structures found in modern forms are homologous, or are the products of convergent evolution.