436 SPECIAL HISTOLOGY. 



many instances, gradually become so much attenuated, as 

 ultimately to measure not more than 0-0008'", 0'0006'", or even 

 hardly O0004"', and present an almost entirely pale aspect, 

 so that they can scarcely any longer he distinguished from the 

 finer processes of the nerve-cells ; -with which in fact, unless 

 everything is deceptive, they most probably are actually con- 

 nected. All the fibres, also, which enter the caudate nucleus, 

 present exactly the same conditions; some of these enter the 

 nucleus directly from the basis of the cerebral peduncle, others, 

 which appear in its thinner portion, are manifestly derived from 

 the lenticular nucleus, the first two divisions of which thev tra- 

 verse in the first instance ; in this case, also, there is no transition 

 of the fibres into the medullary stibstance of the hemispheres, 

 but a separation of the fasciculi into a plexus of the finest, 

 almost non-medullated fibres takes place, and probably a con- 

 nection between them and the cells. 



Besides the above described, in any case very numerous, 

 nerve-fibres derived from the cerebral peduncles and terminating 

 in the corpora striata, the nuclei of those bodies contain a 

 considerable number of other fibres, whose origin it is, in part, 

 difficult, and, in part, impossible to assign. I think I can trace 

 one set of these fibres to their source. In the most external 

 part of the large nucleus of the corpus striatum, we find, on 

 making various sections, a considerable number of moderately 

 strong fasciculi, though not visible to the naked eye, which in 

 their relative thickness and the diameter of their tubes 

 (0-0012 — 0002'") differ from the fibres derived from the crus 

 cerebri, which in this situation are reduced to the most extreme 

 attenuation and dispersed in a plexiform manner. It is easily 

 seen, that all these fasciculi proceed from the medullary sub- 

 stance of the hemispheres ; and, as it appears, after they have 

 run a certain distance parallel with the surface on the border 

 of the nucleus of the corpus striatum, that they enter it. 

 Many of these fibres are continued directly from the medullary 

 substance into the ganglia, and, in this way, decussate, at right 

 angles, with the former fibres. Assembled in fasciculi, these 

 fibres penetrate more or less deeply into the grey substance of 

 the corpus striatum, and of the third division of the lenticular 

 nucleus; and these terminate, as I think I have observed, 

 without any considerable expansion, the formation of a plexus, 



