[The development of the human cerebral cortex. A cytoarchitectonic theory]

In order to understand the over-all organization of the neocortex, its development in the embryos of certain mammals has been studied using the Golgi method.

The neocortex starts its development with a primary plexiform layer in the telencephalon, which precedes and is essential for formation of the cortical plaque. Layer I and the sublayer are derived from this primary plexiform layer which represents the primitive cortical organization shared with reptiles and amphibians. The other layers (II, III, IV, V and VI) are derived from the cortical plaque which is an innovation occurring in mammals. During the development of the cortical plaque, migration, early differentiation and morphological and functional maturity of the neurones occur. The neurones, guided by the radial glia, reach layer I, develop an apical dendrite and establish contact with the cells of Cajal-Retzius, after which the migratory neurones assume a common pyramidal morphology. During ascending cortical maturity, controlled by the thalamus, the neurones acquire their specific morphology and function. The cortical plaque represents a biologically non-specific stratified nucleus which increases the number of pyramidal layers during the evolution of the mammal.

In this paper we emphasis the importance of the Cajal-Retzius cells in neuronal migration, formation of the cortical plaque, morphology of the pyramidal cell and ascending stratification--morphological and functional--of the neocortex. We also introduce a new cytoarchitectonic theory of the phylogenetic evolution of the mammalian neocortex.