[Comparative analysis of the neocortex during the ontogenesis of cetaceae and primates]

Comparative ontogenetic investigation of cytoarchitectonics of the cerebral neocortex has been performed in Cetacea and Primates using paraffin frontal and sagittal cerebral sections stained after Nissl. Cerebral hemispheres of dolphins, whales, monkeys and human being have been studied at various periods of prenatal development and in mature individuals. The comparison has been made at similar stages of cytoarchitectonical differentiation of the cortical plate. At two first stages of the prenatal ontogenesis (formation of the cortical plate and its differentiation into layers) there is not any principle differences between the Cetacea and Primates. Peculiarities of the cerebral cortical plate differentiation in the Cetacea (absence of the internal granular layer IV) is determined at the stage of stratification. Similar agranular character of the cerebral cortex differentiation is maintained during the whole subsequent ontogenesis in the Cetacea (heterogenetic type of the neocortex after Brodman). Absence of the layer IV in the cerebral neocortex determines some other principles in the spatial organization of the cortical-subcortical and in the intracortical connections in the Cetacea brain. This is confirmed by modern data of morphological and electrophysiological investigations. Perhaps, a comparatively more simple initial architectonics of the Cetacea brain limited the level of their functional possibilities, the latter is comparable only with anthropoid apes.