STRUCTURAL ARRANGEMENTS OF CEREBRUM 431 



(b) The relative thickness of the various layers. 



(c) The character of the cells found in the various layers. 



(d) The arrangement and degree of development of the systems of 

 medullated fibres, both radial and transverse. 



The possibilities in such a method are at once apparent if, as in Figs. 221, 

 222 and 223, we compare the structure of the cortex from, e.g. the pre-central 



(5) 

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FIG. 222. Visuo-sensory. 



FIG. 223. Visuo-psychic. 



motor convolution, the visuo-sensory area of the occipital convolution, and 

 the ' visuo-psychic ' area. The finer differences are not so readily perceptible 

 without careful study and measurement of the various layers and the elements 

 constituting them. By this method we can mark out the cortex into areas, 

 which agree closely with the localisation of functions as arrived at by 

 experimental methods or by a study of the systems of fibres in the brain or 

 of the functional defects observed under pathological conditions. 



The localisation arrived at in this way is represented in the diagrams 

 taken from Campbell (Fig. 224). Thus in the motor area, the precentnil 



