3 o 4 NORMAL HISTOLOGY. 



The spaces between these radial bundles are occupied by a delicate 

 interlacement, the interradial feltwork, which is composed in large part 

 of the lateral and collateral processes of the cells. Within the third layer, 

 the horizontally coursing- collaterals and processes of the large pyramidal 

 cells form a complex of unusual intricacy, which condensation gives rise to 

 the outer stripe of Baillarger. Beyond the outer ends of the radial fibre- 

 bundles, the intercellular ground-work is occupied by a second delicate inter- 

 lacement of processes and collaterals, the supraradial feltwork; while 

 immediately beneath the narrow subpial neurogliar zone innumerable delicate 

 terminal nbrillae course horizontally and parallel with the surface and con- 

 stitute the tangential fibre-layer. The components of this layer are the 

 terminal branches of the dendrites of the pyramidal and polymorphic cells 

 and the axones of the cells of Martinotti, as well as the main and secondary 

 processes of the fusiform elements of the stratum zonale. 



Local Variations in the Cerebral Cortex. While in the main 

 certain features are common to the cortex wherever well developed, more or 

 less evident variations occur in different localities. Such variations are, for 

 the most part, slight and depend upon the size and number of the nerve-cells 

 and the richness and direction of the nerve-fibres changes which produce 

 alterations in the relative proportions of the strata. The width of the stratum 

 zonale is almost constant and subject to little modification, being usually well 

 defined from the layer of small pyramidal cells. The layer of the large 

 pyramidal cells, on the contrary, exhibits considerable variation, either in 

 increased thickness, as in the precentral gyrus, or in diminished breadth, as 

 in the occipital lobe. The layer of polymorphic cells is fairly uniform, but 

 within the precentral convolutions is reduced almost to disappearance, 

 although the pyramidal cells of the superimposed (third) layer are here of 

 unusual size. Such variations in the histological features of the cortex are 

 probably correlated with differences in the function of its various regions, 

 although the exact relations between such differences are in many cases still 

 obscure. Disregarding the cortical regions which are profoundly modified 

 by their rudimentary character, such as the olfactory lobe, apart from minor 

 variations in details, the cortex of the greater part of the frontal, parietal, 

 occipital, temporal and limbic lobes and of the insula closely corresponds in 

 its structure. That of the motor (Rolandic) region, of the calcarine (visual) 

 area of the occipital lobe, and of the hippocampus, dentate gyrus and 

 adjacent part of the hippocampal gyrus, however, presents very evident 

 modification. 



The Rolandic cortex of the precentral gyrus, particularly towards the upper margin 

 of the hemisphere, of the paracentral lobule and of the adjoining part of the postcentral 

 gyrus the great cortical motor area of the hemisphere is distinguished by the great 

 breadth of the layer of large pyramidal cells, the unusual size of the last-named elements 

 and the feeble development of the layer of polymorphic cells. The pyramidal cells 

 collectively tend to larger size as the upper end of the precentral convolution is ap- 

 proached and, in addition, cells of extraordinary dimensions appear. These elements, 

 the giant pyramidal or Betz's cell's, reach their maximum size within the paracentral 

 lobule, where some attain a breadth of 65 ji or almost double that of the pyramidal 

 elements in other regions. The giant cells are further distinguished by their robust 

 and rounded form, their distribution in small groups of from three to five in the deeper 

 layers of the cortex, and the exceptional thickness of their axones. 



The Internal Nuclei. Embedded within the white matter of the 

 cerebrum, for the most part completely separated from the cortex, lie certain 

 paired masses of gray matter collectively known as the basal ganglia. 



