BECT. 1 1 6.] 



NERVOUS SYSTEM. 



2 3 5 



outer of which is situated exactly at the place where the bundles 

 penetrating the grey substance arc lost to view. That is to say, 

 as these bundles proceed further outwards they become con- 

 tinually thinner, by giving off lateral branches, and by the 

 attenuation and separation of their elements, till, arrived at 

 the grey layer, they are withdrawn from view; and although, 

 when more narrowly traced, they can be demonstrated, even 

 in this situation, as variously interlaced fibrils of the finest de- 

 scription, with scarcely any appearance of dark contours, only 

 a few of them retain their original breadth and dark con- 

 tours after reaching the pure grey layer, and continue in a 

 straight or oblique Fig. 97. 



course through it, 

 in order to pursue 

 their way further, 

 horizontally, in the 

 outer white layer. 

 In this layer a con- 

 siderable number of 

 tubes, of the finer 

 and very finest kind 

 (fig. 97), decussate 

 in various direc- 

 tions, in several su- 

 per-imposed layers. 

 These are obviously 

 derived principally 

 from the tubes which 

 come from the grey- 

 ish-red layer, and 

 perhaps, also, as 

 Remak assumes, from the knee of the corpus callosum at the base 

 of the brain. 



The relation of these fibres to the cells in the white layer is 

 doubtful ; but this much is certain, that many of them turn back 

 into the greyish-red layer whence they come, — in other words, 

 form loops, which were first described by Valentin, and which I 

 have frequently and distinctly seen in chromic acid preparations 

 treated with caustic soda. In like manner I saw in the 

 greyish-red substance, as well as upon its convexity, directed 

 towards the surface of the brain, separate loops with closely ap- 

 proximated sides. The bundles of the greyish-red substance 



From the inner parts of the erey layer of the convolutions of the 

 human brain; magnified 350 times. Nerve-cells, a, larger, 

 b. smaller; e. nerve-tibres with axis-cylinder. 



