NON-MEDULLATED FIBRES. 



131 



along their length, and contracted in the intervals between the dilated 

 parts. Such fibres have been named varicose (fig. 84). They occur 

 principally in the brain and spinal cord, and in the intra-cranial part 

 of the oltactory, in the optic, and acoustic nerves ; tliey are occasion- 

 ally met with also in the other nerves, especially in young animals. 

 These fibres, however, are naturally cylindrical like the rest, and 

 continue so while they remain undisturbed in their place ; and the 

 varicose character is occasioned by pressure or traction during the 

 manipulation, which causes the soft matter to accumulate at certain 

 points, whilst it is drawn out and attenuated at others. Most probably 

 the change takes place before the white substance has coagulated. The 

 fibres in which it is most apt to occur are usually of small size, 

 ranging from -rTT?T77T)th to ^/.Tnth of an inch in diameter ; and when 



a very small fibre is thus affected, the varicosities appear like a string 

 of globules held together by a fine transparent thread. As already 

 remarked, the double contour caused by congelation of the white sub- 

 stance does not appear in the highly constricted parts. The axis takes 

 no part in this change, indeed it may sometimes be seen running 

 through the varicosities and undergoing no corresponding dilatation. 



Course of the fibres. — Neither in their course along the nervous 

 cords, nor in the white part of the nervous centres, have the medullated 

 fibres ever been observed to nnite or anastomose together, nor are they 

 seen to divide into branches ; it is therefore fair to conclude that, though 

 bound up in numbers in the same nervous cords, they merely run side 

 by side like the threads in a skein of silk, and that they maintain their 

 individual distinctness throughout the trunk and branches of a nerve ; 

 but in many cases the fibres divide in approaching the peripheral ter- 

 mination of the nerve, as will be again noticed. 



Grey, Pale, Non-medullated, or Gelatinous Fibres* (fig. 85.) 

 — The white fibres, at the peripheral extremities of many nerves, lay 





Fig. 85. — NoN-MEDULLATED Nerve-Fibres (Max Schultzc). 

 Magnitied between 400 and 500 diameters. 

 A. From a branch of the olfactory nerve of the sheep ; at a, a, two dark bordered or 

 medullated fibres, from the fifth pair, associated with the pale olfactory fibres. 

 £. From the sympathetic nerve. 



* These fibres were termed "gelatiaous' 

 chemical nature. 



by Heale, from their aspect, not their 



