THE STRUCTURE OF THE CEREBRAL CORTEX 275 



which is characteristic of the several cortical regions in each 

 ' species of mammals, and that this pattern is broadly similar in 

 all of the higher members of this group of animals. 



Data derived from physiological experiments made on dogs, 

 apes and other animals, and from the study of pathological hu- 

 man brains have shown also that the difference in structural 

 pattern of the cortical areas is correlated with differences in 

 the functions performed by them. To these functional ques- 

 tions our attention will next be directed. 



Summary. The cerebral cortex is the organ of the highest 

 individually modifiable functions, particularly those of the 

 intellectual life. It matures late in both phylogenetic and indi- 

 vidual development, and therefore has been called the neenceph- 

 alon. In early developmental stages it forms the roof of the 

 lateral ventricle of each cerebral hemisphere, but in the adult 

 human brain it is so enlarged as to envelop most other parts of 

 the hemisphere. The cortex of the two hemispheres is con- 

 nected by commissural fibers in the corpus callosum and the hip- 

 pocampal commissure. The various regions of each hemisphere 

 are connected by a complex web of association fibers, and some 

 parts of the cortex are connected with subcortical regions by 

 1 projection fibers. The sensory projection fibers discharge 

 among the neurons of the sensory projection centers, and the 

 motor projection fibers arise from neurons of the motor projec- 

 tion centers. The intervening association centers are connected 

 with the projection centers and with each other by very intricate 

 systems of association fibers. The cortex is laminated by bands 

 of horizontally arranged nerve-fibers and by an arrangement of 

 its cells in layers. The pattern of this lamination varies in 

 different regions, and charts of these structurally defined regions 

 are found to show a general correlation with the functionally 

 defined areas as physiologically and pathologically determined. 



IV. Lamina granularis interna, or inner granular layer, containing the 

 medullated fibers of the external line of Baillarger (in the visual area called 

 the stripe of Gennari). 



V. Lamina ganglionaris, or layer of large cells, containing in the motor 

 area the giant pyramidal cells or Betz cells, from which the fibers of the 

 pyramidal tract arise, and containing in most areas the medullated fibers of 

 the internal line of Baillarger. 



VI. Lamina multifonnis, or layer of polymorphic cells. 



