CHAP. IT.] THE BRAIK 801 



probable endings in contact with motor cells which seem to 

 afford the mechanism for many reflex actions, we may distin- 

 guish at least two other kinds of ending. We have reason to 

 think that some of the fibres make connections by contact with 

 the cells of the vesicular cylinder, Clarke's column. We have 

 further reason to think that axis-cylinder processes of these 

 cells of the vesicular cylinder, go to form the cerebellar tract, 

 which we may assume to be an afferent tract, arid which may 

 be traced through the restiform body to the cerebellum in 

 connection with certain cells of which, especially those of the 

 nucleus dentatus, the fibres of the tract end. Now though the 

 cerebellum is connected, in an indirect way it is true, with 

 the cerebral cortex we have no grounds for thinking that the 

 cerebellum is concerned with the development of the sensations 

 with which we are now concerned : when the whole cerebellum 

 is removed there is no apparent affection of cutaneous sensations. 

 We may therefore dismiss the cerebellar tract; the afferent 

 impulses passing along it have probably to do with the coordi- 

 nation of movements affecting equilibrium, but they are not 

 the impulses which become developed into conscious sensations 

 of touch or of pain. 



The other fibres of the posterior root of which we are 

 speaking end in connection with other cells of the grey matter. 

 From these cells we have reason to think fibres originate and 

 pass upward in the white matter. Some of these we may 

 distinguish as the ' ascending antero-lateral ' tract ; but our 

 knowledge here becomes less definite. Some of the processes 

 of the cells, with which the posterior root fibres make connec- 

 tion, end as they begin within the grey matter of the cord itself, 

 in connection with other cells of the grey matter; and even 

 those which travel beyond the cord appear to go no farther than 

 the bulb, ending in connection with cells in that structure, more 

 particularly with the cells of the gracile and cuneate nuclei. 

 So far as our present knowledge goes there is no definite tract 

 from various parts of the cord to the brain comparable to the 

 pyramidal tract from the brain to various parts of the cord. 

 The passage of afferent impulses on their way to become con- 

 scious sensations is from the first a system of relays. There is 

 a first relay where the ending of the root fibre makes connec- 

 tions with a nerve cell in the adjoining grey matter, or in the 

 gracile nucleus. There is in the former case a further relay in 

 the bulb at least, and possibly in some instances other relays 

 in the grey matter of the cord on the way. The path to the 

 bulb thus supplied by the fibres and their relays, keeps to a 

 large extent on the same side of the cord, though some cross- 

 ing is observed. 



From the bulb onwards one definite path only, and that a 

 narrow one, is marked out anatomically by the median fillet 



51 



