424 



THE TISSUES. 



The length of the nerve-fibres also varies extremely ; since they 

 have one extremity in the part where they are distributed, while 



the other enters the ence- 

 Fig. 272. , , . , 



phalon or spinal cord (to 



constitute their white or 

 fibrous portions), or termi- 

 nates in ganglia. 



J. 



1. The Coarse (large) Nerve- 

 Fibres. 



It is, of course, impossible 

 to draw any precise line 

 between the coarse and the 

 medium nerve-fibres, since 

 all grades of size are found 

 between their extremes of 

 Y^fl of an inch as the dia- 

 meter of the coarsest, and 



343SU as tnat f tne finest 

 fibres. Nor is it of any 

 importance that the inter- 

 mediate should be distin- 

 guished as such; since they 

 appear to present no pecu- 

 liarity in structure or func- 

 tion. Kolliker, however, 

 mentions as coarse fibres 

 those above ^ ^V u f an inch; 

 as medium those from gTJ ^ 



visiuie wiuiiu mw nure. u. JL wo isoiaitsu axis-tiures , , n -i -\ 



from the cord, one undulated, the other of unequal thick- ' 3^0 IT Ot an mcn J ancl as 



ness, with some medullary substance attached to it. fine those leSS than RTyVs of 

 Magnified 350 diameters. (Kottiker.) 



an inch. 



All the nerve-fibres, when examined in their recent state, and 

 by transmitted light, appear perfectly transparent, and with simple 

 dark contours. By reflected light they appear opaline, like fat, and, 

 in large quantities together, white; but generally they do not ap- 

 pear to be composed of different constituent parts. 



All the coarse fibres may, however, be shown to consist of (Fig. 

 273, and Fig. 272, 3,4) 



Nerve-fibres. 1. From the dog and rabbit, in their na- 

 tural condition : a, fine ; b, of medium thickness ; c. coarse 

 fibre from the peripheral nerves. 2. From the frog, with 

 the addition of serum : a, drop of the contents expressed ; 

 &, axis-fibre within the drop continued into \the tube. 

 3. From the spinal cord of man ; recent, with serum add- 

 ed : a, neurilemma ; 6, medulla with double contour ; c, 

 axis-fibre. 4. Double contoured fibre from the fourth 

 ventricle in man ; the axis-fibre (a) projecting, and 

 visible within the fibre. 5. Two isolated axis-fibres 



