1863.] 717 



first or superficial layer is a comparatively thin stratum of fine and 

 closely-packed fibres, intimately connected externally with the pia 

 mater with which they are very liable to be torn away while in- 

 ternally they are continuous with fibres radiating from the grey 

 substance. 



The second layer is of a pale or whitish colour, and several times 

 the thickness of the one just described. It consists, first, of fibres 

 running parallel with the surface, both around the convolution and 

 longitudinally ; secondly, of fibres radiating across them from the 

 grey substance beneath, and crossing each other with different 

 degrees of obliquity ; and thirdly, of a small number of scattered 

 nuclei, which are round, oval, fusiform, or angular, and have their 

 longer axes in different directions, but mostly within-outward. 



The third layer is of a grey colour, from two to four times as 

 thick as the one above it. It is densely crowded with cells of small 

 size, but of different shapes, in company with nuclei like those of the 

 preceding layer. The cells are more or less pyriforni, pyramidal, 

 triangular, round and oval, or fusiform. The pyriform and pyramidal 

 cells especially in the outer portions of the layer lie for the most 

 part with their tapering ends toward the surface ; and the oval and 

 fusiform cells have generally their longer axes and their processes in 

 a similar direction. In the deeper portions of the layer, however, 

 their position is more irregular, many of them lying with their 

 longer axes parallel with the surface, and in connexion with a multi- 

 tude of fibres which run in the same direction and in great number 

 along the layer. They contain each a comparatively large granular 

 nucleus, which frequently nearly fills the cell. Two, three, four, or 

 more processes spring from the broader ends of the pyramidal cells, 

 and run partly toward the central white substance, and partly in 

 the plane of the layer, to be continuous with nerve-fibres in different 

 directions. 



The fourth layer is of a much paler colour. It is crossed, how- 

 ever, at right angles to its plane, by narrow long and vertical 

 groups of small cells and nuclei of the same general appearance as 

 those of the preceding lamina. These groups are separated from 

 each other by bundles of fibres radiating toward the surface from 

 the central white substance, and, together with them, form a beau- 

 tiful and fan-like structure. This layer is distinguishable from the 



VOL. XII. 3 E 



