958 THE CENTRAL NERVOUS SYSTEM 



indicated that in the lower apes also excitation of the gyrus post- 

 centralis does not cause movements (C. and O. Vogt). 



It is in the light of the results obtained in monkeys, and by the 

 aid of histological, embryological, clinical, and pathological ob- 

 servations, that the ' motor ' areas in man have to a great extent 

 been mapped out. 



The histological differentiation of the various cortical regions recently 

 demonstrated by Brodmann and by Campbell are of especial interest 

 (Figs. 387-391). It has long been customary to divide the cortex into 

 layers, although the number and the boundaries of these layers are 

 somewhat arbitrarily fixed. Brodmann distinguishes six layers: (i) A 

 zonal or peripheral layer, containing many nerve-fibres and neuroglia 

 cells, but few nerve-cells; (2) a layer containing ' granules ' and small 

 pyramidal cells (external granular layer) ; (3) a layer of medium and 

 large pyramidal cells (pyramidal layer) ; (4) a layer of small irregular 



* . 



5 





Fig. 387. Cell- Lamination of Gyrus Postcentralis (Campbell). A, just behind 

 upper end of fissure of Rolando; B, from the posterior edge of the gyrus (inter- 

 mediate postcentral area of Campbell). 



cells (internal granular or stellate layer) ; (5) a ' ganglionic ' layer, con- 

 taining the largest pyramidal cells (deep large pyramids); (6) a layer 

 (lamina multiformis) of spindle-shaped or polymorphous cells. These 

 layers vary in their structural details, and especially in their relative 

 development in animals of different rank in the mammalian scale, in 

 one and the same animal at different periods in its embryonic and 

 extra-uterine growth, and also in different parts of the cortex in an 

 adult animal of given species. The region in front of the central 

 sulcus (fissure of Rolando), e.g., if, characterized by the presence of the 

 giant pyramids of Betz, which give origin to the pyramidal fibres 

 going to the trunk and limbs (Fig. 388). More than forty years ago 



