COURSE OF KEEVE-FIBRES. 



469 



of the substance corresponding with the central portion, or 

 axis-cylinder of the larger fibres. Yet since many nerve- 

 fibres may be found which appear intermediate in character 

 between these two kinds, and since the large fibres, as 

 they approach both their central and their peripheral end, 

 gradually diminish in size, and assume many of the other 

 characters of the fine fibres of the sympathetic system, it 

 is not necessary to suppose that there must be a material 

 difference in the office or mode of action of the two kinds 

 of fibres. 



Every nerve-fibre in its course proceeds uninterruptedly 

 from its origin at a nervous centre to near its destination, 



Fig. 135*. 



whether this be the periphery of the body, another nervous 

 centre, or the same centre whence it issued. 



* Fig. 135. Small branch of a muscular nerve of the frog, near its 

 termination, showing divisions of the fibres, a, into two ; &, into 

 three ; magnified 350 diameters (from Kolliker). 



