THE FUNCTIONS OF THE CEREBRAL CORTEX 289 



arising from the precentral gyrus. Each of the thalamo-cortical 

 projection tracts of vision, hearing, and tactile sensibility is, 

 moreover, accompanied by cortico-thalamic fibers which conduct 

 in the reverse direction and whose functions are not well known, 

 and there are other cortico-thalamic and cortico-mesencephalic 

 systems. The cerebral cortex is in direct connection with the 

 red nucleus of the cerebral peduncle by a cortico-rubral tract, 

 arising in the frontal region of the cortex, and by ascending 

 fibers from the red nucleus to the same general part of the 

 cerebral hemisphere. From the frontal, parietal, temporal, and 

 occipital association centers there arise large descending fiber 

 tracts to the nuclei of the pons (cortico-pontile tracts). These 

 connections between the cerebral cortex and the red nucleus 

 and pons put the cerebral cortex and the cerebellum into very 

 intimate relations, but the exact way in which the cerebrum and 

 the cerebellum cooperate functionally is obscure (see p. 192). 



From the preceding account it is plain that the cerebral cortex 

 is structurally differently organized in different parts, and that 

 each of these parts has its own characteristic fiber connections. 

 Physiological experiment and pathological studies have shown, 

 moreover, that some of these regions, the projection centers, are 

 functionally diverse, in that each one receives a particular type 

 of afferent fibers or discharges efferent impulses into a definite 

 subcortical motor center. Stated in other words, the cortex is 

 structurally a mosaic of diverse patterns ; and on the physiolog- 

 ical side there is a specific localization of function, at least in the 

 sense that the various systems of afferent and efferent projection 

 fibers connect each with its particular place in the structural 

 mosaic. 



Several English neurologists, notably Bolton, from studies on the 

 development and adult structure of the cortex in normal and abnormal men 

 and in other mammals, have been led to the conclusion that, in addition to 

 the mosaic localization pattern of which we have been speaking, there is a 

 functional difference between the different layers of neurons of the cortex 



the somesthetic area (2, 26, 2c, and 8), the visual area (7 and probably 76), 

 and the gustatory area (46 and 6). The remainder of the cortex is made up 

 of association centers, of which there are two groups, those which mature 

 soon after birth (lightly shaded areas 13-28), and the terminal areas (un- 

 shaded areas 28-36) which are the last to mature. (From Lewandowsky's 

 Handbuch der Neurologic.) 



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