CHORD, WITH FURTHER INVESTIGATIONS INTO ITS STRUCTURE. 
355 
direct continuity between the cerebral fibres and the caudate vesicles of the chord, I 
arn disposed to think it is established by means of the system of fine nerve-tubes 
which are seen to proceed from the grey substance of the latter as longitudinal fibres 
of the white columns. In opposition to Wagner, I agree with Kolliker in the 
opinion that the process of a nerve- vesicle never becomes the axis-cylinder of a double- 
contoured nerve-tube, and that what Wagner considered as the process of a nerve- 
vesicle was probably the axis-cylinder itself. The evidence of any direct connection 
between these processes and the roots of the nerves is very unsatisfactory; for 
amongst thousands of preparations examined by myself with the greatest care, I met 
with a few cases only in which it was at all probable. 
If any of those fibres of the posterior roots, which, after traversing the grey sub- 
stance, enter the anterior white columns, could be proved to extend as far as the 
brain, the indications of sensation which are said to have followed irritation of these 
columns might be thus explained. It is quite certain, however, as already stated, 
that an equal number of those fibres pursue a downward course. On the other hand, 
if the anterior columns really be, as I believe they are, one of the channels which 
transmit downwards the influence of the will, they can perform this office only by 
first entering the grey substance, since into this all the fibres of the anterior roots 
may be traced. The same inference may be drawn with regard to the lateral white 
columns, which from their connection, through the grey substance, with the roots of 
the nerves, would appear to be both sensitive and motor. 
The fact that many fibres of each root, on entering the grey substance, not only 
extend both upwards and downwards to a considerable distance beyond their point 
of entrance, but intermingle also in the most intricate manner with those of other 
roots, may serve to explain how impressions made at one particular spot are com- 
municated in different directions to distant parts of the chord, so as to excite a 
simultaneous and sympathetic action in classes of muscles which otherwise would 
appear unconnected. It is probable that the fibres which quit the grey substance 
and return to it by the formation of loops within the white columns, may take that 
course for the purpose of stimulating particular parts of that substance, without 
affecting those which are intermediate. 
In concluding this series of investigations, it has appeared to me, that, considering 
the beauty and transparency of my preparations, the distinctness with which their 
several parts are preserved, and the persevering labour which has been bestowed 
upon them, I might almost venture to think we have obtained nearly all that it is 
possible to know — with our present means — concerning the minute anatomy of the 
spinal chord. Our further progress is arrested chiefly by the continual and intricate 
deviations observed in the course of its fibres, and the consequent disorder in which 
its elements appear to be involved, when viewed in section. The confusion, how- 
ever, is doubtless only apparent ; for in this wonderful organ, with all its complexity 
of structure, we have no reason to doubt the constant and uniform existence of that 
