442 



SPECIAL HISTOLOGY. 



perceived as intricately interlaced fibrils of the utmost 

 fineness, and with scarcely any appearance of dark contours, 

 only that there are a certain, though smaller number of fibres, 

 which, upon reaching the grey layer, do not lose their breadth 

 and dark contours, but are continued in a straight or oblique 

 course through it, extending horizontally to a further distance, 

 in the outer white layer. In this layer, consequently, we 

 find a considerable number of finer, and of the very finest 

 fibres (fig. 150), crossing each other in various directions, and 



in several superim- 

 posed layers, which are 

 obviously, as to their 

 origin, to be referred 

 to those arising from 

 the reddish-grey layer; 

 and which probably 

 also, as Remak has as- 

 sumed, are derived, at 

 the basis of the cere- 

 brum, from the an- 

 terior extremity (knee) 

 of the corpus callosum. 

 How these fibres are 

 related to the cells in 

 the white layer is 

 doubtful, although this 

 much is certain, that many of them return into the grey-red 

 substance from which they arose, or in other words form loops, 

 which were first described by Valentin, and which I have very 

 frequently and distinctly noticed in chromic acid preparations 

 treated with caustic soda. I have also observed, in the grey- 

 red substance, isolated loops with closely approximated sides, 

 and also with their convexity looking towards the surface of 

 the brain. The fasciculi of the grey-red substance contain 

 fibres which, at first, measure 00012 — 0-003'", but almost all of 

 which ultimately decrease in size down to 0-00 1'", and, in the 

 grey substance, acquire the diameter of the smallest nerve- 

 tubes, 0-0004 — 0-0008'". The fibres given off from these 



Fig. 150. Finest nerve-tubes of the superficial white substance of the human 

 cerebrum, x 350 diam. 



