Comparative neuroanatomy: place, principles, practice and programme.

In this paper an outline is presented of the foundations of comparative neuroanatomy. The significance of topology (i.e. the geometry of distortion) for an accurate analysis of the kinds of morphological transformations to which central nervous systems are subjected is emphasized. The major tasks of comparative neuroanatomy are: (1) to sample the variation existing in the central nervous systems on the basis of an analysis of a multitude of carefully selected species; (2) to place the patterns of variation found, wherever possible, in an phylogenetic context; (3) to relate the morphological data and relations determined, to their putative biological (functional, behavioural) significance, and (4) to reflect on the question of which specific factors and processes might have caused the changes through which the brains of organisms have passed, and to develop explanatory scenarios.