[Quantitative characteristics of the inferior parietal cortical formation of the chimpanzee cerebrum]

In histological preparations of the left and right hemispheres a layer-by-layer investigation of cyto- and myeloarchitectonics of the radial system of fibers in the inferior parietal formation (fields 40, 39) has been performed; it is the homologue of the human inferior parietal formation and in chimpanzee it is immediately connected with manipulatory activity. The width of the cytoarchitectonic layers is measured, and in the fibrous layers 4, 5 and 6--also caliber (diameter) of the fibrous fasciculi and fibers in the fasciculi. Statistical parameters of distribution density of the layer widths, caliber of the fasciculi and fibers are estimated. The degree of their changeability is great. The variability coefficient of the layer widths is statistically significant, and there are no interhemispheric differences in width of analogous layers of both fields. Caliber of the fasciculi in the left and right hemispheres is distributed asymmetrically, being greater in the field 39 than in the field 40 of the right hemisphere. Similar regularity in the field 39 is noted in distribution of fibers. Overwhelming majority of fibers in the field 39 have, in comparison with the field 40, greater caliber. The data obtained demonstrate heteromorphism of the radial system in the fibers of the chimpanzee inferior parietal formation. This, evidently, ensures conduction of impulses of various modality.