THE NERVOUS SYSTEM. 381 



close to the ferrngineous layer, and tliej are, not unfrequently, at least 

 some of them, partly imbedded in its nuclei, in single or multiple layers, 

 and presenting 2-3, rarely 1-4, long and much branched processes, 

 directed particularly towards the outer surface of the convolutions, Avhich 

 are, almost without exception, at all events the strongest of them, given 

 off from the sides of the cells which look from the ferrngineous layer. 

 At their origin these processes are even 0-007, or as much as 0*008 of 

 a line thick, and extremely finely granular or very delicately striped. 

 As they proceed they become more homogeneous, and at the same time 

 divide into very numerous and extremely slender branches, so that at 

 last, from each process a large bundle of very fine filaments, having a 

 diameter, in the finest, of scarcely 0-0002 of a line, is produced, A 

 portion of these fibrils penetrate more horizontally into the gray layer, 

 although most of them stretch directly outwards, and appear to extend 

 nearly to the outer surface of the gray layer. That they extend very 

 far is certain, for in preparations made with chromic acid, I have iso- 

 lated some measuring 0-15-0-2 of a line, which were still not the finest ; 

 and in successful perpendicular sections through the cortical layers of 

 the convolutions, their principal branches appear as parallel, slightly 

 undulating fibres in close contiguity, extending through more than two- 

 thirds, or even three-fourths, of the gray layer, to which they give a 

 peculiar striated aspect. Whilst the principal prolongations of the pro- 

 cesses are, in this way, continued through the gray layer, they give off 

 their branches at acute or right angles, whence not unfrequently a 

 second striation is produced, crossing the one just described at a greater 

 or less angle. 



In the innermost portion of the gray layer, among the large cells, 

 there moreover exists some nerve-jihres ', but which, owing to their deli- 

 cacy and the ease with which they are destroyed, it is very difiicult to 

 trace. Quitting the ferrugineous layer, and forming a continuous plexus, 

 they are distributed in the inner third of the gray lamina among the 

 large cells and their processes ; there mode of termination has escaped 

 my observation, the result of Avhich amounts only to this : 1, that they 

 become finer and paler, decreasing from their original thickness of 

 0-0012, ultimately to one of 0-OOOG and 0-0004 of a line, their dark 

 outlines also being replaced by a paler contour ; 2, that they certainly 

 do not form terminal loops, such as Valentin and Hyrtl, who have pro- 

 bably mistaken a fine plexus for such, think they have noticed ; but be- 

 coming isolated, and running in a more straight direction, and almost 

 as pale as the processes of the nerve-cells at the border of the inner 

 third of the gray lamina, are lost towards the middle of it. 



The crura cerehelli are composed of nothing but parallel nerve-fibres, 

 •without any admixture of gray substance, corresponding with those of 



