168 



THE CEREBRAL HEMISPHERES. 



frequently come off from the dendrites, instead of, as is usual, from the body of the 

 cell (Cajal). 



2. Layer of small pyramids. This layer, of nearly the same thickness as the 



Fig. 116. SECTION OF CEREBRAL CONVOLUTION 

 (Meynert). 



1, Superficial layer, with scattered cells ; 2, layer 

 of small pyramidal cells ; 3, broader layer of pyra- 

 midal cells, separated into columns by the radiating 

 nerve-fibres ; 4, narrow layer of small irregular cells ; 

 5, layer of fusiform and irregular cells in medullary 

 centre. 



last, is characterized by containing a large 

 number of small nerve-cells, mostly pyra- 

 midal, with dendrites extending mainly 

 into the superficial layer, and an axis- 

 cylinder process, which starts from the 

 base of the cell and after giving off a few 

 collaterals, passes downwards to the white 

 centre, possibly to the corpus striatum 

 as a projection-fibre. Some of the axis- 

 cylinder processes do not, however, reach 

 the white matter, but end in arborisations 

 between the cells of the next layer. 



3. Layer of large, pyramids. The third 

 layer is of paler tint and much greater 

 thickness. It contains pyramidal branching 

 cells, some large others smaller, arranged 

 with the pointed extremities towards the 

 surface of the convolution, and separated 

 into groups by the bundles of radiating 

 nerve-fibres. The innermost portion of the 

 layer, in which the cells are larger and the 

 separation into groups more distinct, is 

 sometimes described as a separate layer. 

 The axis-cylinder processes of these cells 

 give off 7 or 8 collaterals, which become 

 medullated and end by ramifying in the 

 adjacent grey substance. The axis-cylin- 

 der is then continued on into the white 

 matter as a medullated fibre. 



4. Layer of polymorphous cells. The 

 fourth layer is narrower, and contains 

 many small, irregularly-shaped corpuscles, 

 with numerous dendrites and a single axis- 

 cylinder process. The axis-cylinder pro- 

 cesses of most of these cells tend towards 

 the white centre, but some pass peripher- 

 ally, and reach the molecular layer where 

 they become continuous with some of the 

 nerve-fibres of that layer. 



5. Layer of fusiform cells. The fifth 

 layer, of greater width than the last, and 

 blending more or less with it, is com- 



