SPECIAL HISTOLOGY. 



hemispheres of the brain consists entirely of nerve-fibres, of 0-00012- 

 0-003, on the average 0-002 of a line in size, without any admixture 

 of gray substance. These fibres, of whose special course, we, as yet, 

 know extremely little, never form plexiform interlacements or fasci- 

 culi, but all run in parallel, and most generally, straight lines, and 

 undoubtedly proceed from the corpus callosum and ganglia of the cere- 

 brum as far as the superficial gray substance, whilst it must remain 

 undetermined whether, in their course, they divide or not. But besides 

 these fibres, omitting also the commissura anterior, ihefornix, and the 

 origin of the optic nerves, the hemispheres contain others crossing the 

 former at right angles. I have found these fibres, in the first place, on 

 the outer side of the corpus striatum, in which situation they are to be 

 referred, in part, to the fibres which enter the corpus striatum from the 

 hemispheres and terminate in it ; perhaps, also, in part, to the expan- 

 sion of the corpus callosum in the inferior lobes ; and secondly, in the 

 most superficial layer of the white substance, near the gray cortical sub- 

 stance, where they occur in not inconsiderable numbers, and running, in 

 part, obliquely ; but of their origin nothing satisfactory could be ascer- 

 tained. Whether there are still other, and what traces of fibres, the 

 future must show. 



The more intimate structure of the gray substance of the convolutions 

 is tolerably manifest (vid. "Mikroskop. Anatomie," PL IV. fig. 2). It 

 is most conveniently divided into three layers, an external, white ; a 

 middle, pure gray ; and an internal, yellowish red. The latter, in thick- 

 ness almost equal to the other two, usually presents, on its outermost 

 border, a clear, frequently white streak, and occasionally, more inter- 

 nally, a second, thinner and less white layer, so that there are in fact 

 four or even six successive laminse ; 1, a yellowish-red layer (inner part) ; 

 2, the first white streak ; 3, yellowish-red layer (outer part) ; 4, second 

 white streak ; 5, the gray layer ; 6, superficial white layer. The gray 

 substance contains, in its whole thickness, both nerve-cells and nerve- 

 fibres ; and besides these, much granular matrix-substance, exactly like 

 that of the cerebellum. The nerve-cells are not easily investigated, 

 except in preparations in chromic acid, and in all the three layers they 

 agree in this respect, that by far the greater number of them are fur- 

 nished with from one to six processes, which give off numerous branches, 

 and ultimately form extremely fine, pale fibrils of about 0-0004 of a line 

 in diameter, differing, however, in respect of size, number, &c. In the 

 superficial white layer the cells are few, small (0-004-0-008 of a line), 

 with one or two processes, and scattered in an abundant, finely granular 

 matrix. The middle or pure gray layer, most abounds in cells, which 

 in it, are closely aggregated also in a granular matrix. Their size 

 varies very considerably, some being very small (0-0030*005 of a line), 

 frequently appearing as little more than nuclei, whilst there are many 



