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Abstract
The number of neuronal cell bodies has been counted in a narrow strip (30 micrometers)
through the depth of the neocortex in several different functional areas (motor, somatic
sensory, area 17, frontal, parietal and temporal and in many species (mouse, rat,
cat, monkey and man). With the exception of area 17 of the visual cortex in a number
of primates the same absolute number (congruent to 110) of neurons has been found
in all areas and in all species. In the binocular part of area 17 of the primates
there are approximately 2.5 times more neurons. Thus in mammalian evolution the area
of the neocortex increases in larger brains but the number of neurons through the
depth remains constant, except in area 17 of primates. From these and other findings
it is suggested that the intrinsic structure of the neocortex is basically more uniform
than has been thought and that differences in cytoarchitecture and function reflect
differences in connections.