CHAPTER IX. 



THE INTERMEDIATE PRECENTRAL AREA. 



THE necessity for contrasting the structure and discussing the function of the pre- and 

 post-Rolandic cortex conjunctively was so strong, that I have been prevented from considering 

 tin- area for which I now claim attention in its proper place, in connection with the "precentral" 

 or motor area. That it bears a structural likeness to the " precentral " cortex I hope to place 

 beyond question, and that physiological affinities likewise exist seems extremely probable. 

 Indeed the principal themes arising for discussion in this chapter all bear on the motor function ; 

 they include a consideration of the possible share taken by this cortex in the execution of 

 what we understand by skilled movements, of the stability of the term " psycho-motor," and 

 of the exact localisation of the cortical realm dominating the motor speech mechanism. And 

 in reference to the last topic it is interesting to know that the " intermediate precentral " 

 field embraces the classical area of Broca. 



TYPE OF FIBRE-ARRANGEMENT. (Plate XXI, fig. 1.) 



On examining with the naked eye a transverse section of the " precentral " and " inter- 

 mediate precentral " cortex, stained for the display of its contained nerve fibres, it may be 

 noticed, on passing from behind forwards, that although the transition in character from one 

 type to the other is by no means abrupt, still a diminution in the intensity of coloration of 

 the cortex, particularly of the radiary zone, signals the advent of the " intermediate " 

 arrangement. This change in the colour-tone betokens a decrease in the general fibre-wealth, 

 and as a result the line of Baillarger acquires a distinctness it did not have before, and, 

 moreover, becomes reduplicated. But it is curious to observe that the general fibre-loss is not 

 accompanied by a noticeable reduction in cortical depth. 



Examined under a microscope the following details become apparent. 



Zonal Layer. 



The passage from typical " motor " to " intermediate " cortex is marked by a distinct 

 deterioration in the representation of the zonal layer. The band formation loses in density 

 and its lower border becomes ill-defined. 



The layer is mainly composed of delicate varicose fibrils, only a few varicose fibres of the 

 coarse variety are recognisable, and the large evenly-medullated elements so characteristic 

 of the typical motor cortex are decidedly scarce. These observations apply to appearances seen 

 in the middle of the area, for the representation is better in the immediate neighbourhood of 



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