ABSTRACT
General principles of fundamental organization could be determined by comparative studies of how parts and functions are correlated in different groups. A comparative approach using anatomy and physiology in studying the auditory modifications of heteromyid rodents has yielded several correlations. The concepts of the uniqueness of the mammalian forebrain were based on broad comparative studies of the forebrain in many vertebrates. Nonmammalian vertebrates have no six-layered neocortex, and until very recently there have been no data on projections of nonolfactory sensory modalities to their forebrain. Experimental neuroanatomy particularly using degeneration techniques has yielded results that force a revaluation of the old ideas on the evolution of the vertebrate forebrain. Only mammals were thought to have visual, auditory, and somesthetic projections to the dorsal thalamus and the neocortex the sensory systems were thought to terminate at midbrain levels in nonmammalian vertebrates.
