340 MANUAL OF HISTOLOGY. 



with higher functions, with those of perception, and of directing voluntary 

 and reflected motion. Thus we find the latter structures in the grey 

 matter of the brain, spinal cord, and ganglia, to which we have long been 

 compelled by experience to ascribe reflex functions. They are met with, 

 also, at some other points where their significance is not yet quite appa- 

 rent, as, for instance, among the terminal ramifications of some of the 

 higher nerves of sense. 



With regard to the nerve tubes, we have learned from the last section 

 that their varieties of form and thickness do not go hand and hand with 

 functional differences. Thus the sensitive roots of the spinal nerves con- 

 tain fibres which differ in no respect from those of the motor roots. In 

 the sympathetic system we meet with Remakes fibres, whose nervous 

 nature would seem to be almost beyond doubt, and to these the most 

 analogous formations are the nerve tubes of the olfactory nerve. The 

 fine medullated nervous fibres can with as little right be looked upon as 

 a special sympathetic form, presiding over peculiar functions, as was 

 formerly ' maintained by Volkmann and Bidder; for numbers of inter- 

 mediate grades between coarse and fine tubes are met with at points 

 where there can be no suspicion of sympathetic influence. In this 

 respect the accurate microscopical analyses of recent times has greatly 

 modified the sanguine expectations of an earlier epoch. 



On the other hand, some important aids to physiology have been 

 acquired through the knowledge of the finer anatomy of the nerve fibre. 

 All observers concur in regarding the continuity of the nerve tube as 

 certain, a point necessarily accepted as indispensable by the physiolo- 

 gist, likewise in respect to the isolated course of the latter. Thus we see 

 everywhere the same state of things ; the nerve fibre taking an unin- 

 terrupted course through the long interval between the nervous centre 

 and the place of its final termination, although this course may be modified 

 somewhat by the insertion of a ganglion cell. The question as to what 

 part of the nerve tube is to be looked upon as the realty active, i.e., 

 conducting medium, may perhaps be answered in favour of the axis 

 cylinder, in that it is frequently the only portion present at the origin of 

 the nerve fibre, and probably always at its ultimate termination, whilst 

 the medullary and primitive sheath enclosing it are here absent. At 

 those contracted portions of the fibre, also, which are seen at points 

 where branches are given off, the axis cylinder may present itself for a 

 short distance divested of its usual medullary envelope. The theory of 

 the termination of the nerves in loops having been shown to be incorrect, 

 has given further support anatomically to the theory of isolated conduc- 

 tion. The separate termination of the nerve fibre, whether single or with 

 many ramifications, is also consistent with the views of the physiologists 

 of the present day. The splitting up by which, as we have seen in the 

 nerves supplying muscle, a primitive fibre may become resolved into a 

 multitude of branches, must be looked upon as an ingenious provision of 

 nature for obtaining as highly nervous a periphery as possible, both sensi- 

 tive and motor, with comparatively thin nervous trunks. This arrange- 

 ment seems certainly to have the character of something belonging to a 

 lower order of creation, for the higher we ascend in the animal kingdom, 

 the more do the numbers of tubes and muscle fibres become alike, as we 

 have already remarked above. An acquaintance with the terminal appa- 

 ratus of motor nerves is, also, another important advance recently made. 

 Regarded from a physiological aspect, Krause's and Kuhne's discovery of 



