718 [Recess, 



one immediately above it by a tolerably sharp outline, but internally 

 it gradually passes into, or blends with, the next one below it, or the 

 fifth lamina. 



This fifth layer consists of the same kind of vertical and radiating 

 groups of small cells and nuclei ; but the groups are broader, more 

 regular, and, together with the bundles of fibres between them, 

 present a more distinctly fan-like arrangement. 



The sixth layer is again paler, and somewhat whitish, but contains 

 some cells and nuclei which have a general resemblance to those of 

 the preceding layers and are arranged only in a faintly radiating 

 manner. 



The seventh layer is of a reddish-grey colour, of about the same 

 depth as the preceding, and contains the same kind of cells and 

 nuclei, but in much greater numbers, and mixed with some others of 

 rather larger size : only here and there they are gathered into the 

 small elongated groups which give the appearance of radiations. 

 On its under side it gradually blends with the central white layer, 

 into which its cells are scattered for some distance. Both this and 

 the preceding lamina are traversed by nerve-fibres which run along 

 their planes, or parallel with the surface of the convolution. 



The eighth layer is the central white stem or axis of the convolu- 

 tion. As just stated, it contains, for some distance below its summit, 

 a gradually diminishing number of scattered cells and nuclei, extend- 

 ing from the lower side of the next upper layer. The cells are all 

 separate, and disposed with their longer axes at right angles to the 

 curved surface of the convolution, and therefore in the direction of 

 the fibres radiating from the central white stem, with which some, at 

 least, are continuous*. 



Course of the Fibres of the Central White Substance through the 

 Convolutions. From the central white stem bundles of fibres diverge 

 m all directions, in a fan-like manner, toward the surface of the con- 

 volutions. As they pass between the long and vertical groups of cells 

 (already mentioned) in the inner grey layers, some of them become 

 continuous with the processes of the cells, and others turn round to 

 become horizontal, both in a transverse and longitudinal direction 



* The presence of small cells and nuclei in the white substance of the cerebrum 

 and cerebellum, as well as of the spinal cord, was before pointed out by myself. 

 See Phil. Trans. 1859, p. 442 (note). 



