cxxxviii 



NERVOUS SYSTEM. 



globules held together by a fine transparent thread. As already remarked, 

 the double contour caused by congelation of the white substance 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. 



Neither in their course along the nervous cords, nor in the white part of 

 the nervous centres, have these tubular fibres ever been observed to unite or 

 anastomose together, nor are they seen to divide into branches ; it is there- 

 fore 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 termination of the nerve, as will be again noticed. 



Grey, Pale, Non-medullated, or Gelatinous Fibres (fig. LXXVI). The white 

 fibres, at the peripheral extremities of many nerves, lay aside their medul- 

 lary sheath and dark borders, and are prolonged into pale fibres, often 



Fig. LXXVI. 

 A 



Fig. LXXVI. GREY, PALE OR GELATINOUS NERVE-FIBRES (from Max Schultze. 

 Magnified between 400 and 500 diameters). 



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

 or white fibres, from the fifth pair, associated with the pale olfactory fibres. 



B. From the sympathetic nerve. 



minutely dividing, which seem to represent the axis-cyliuder deprived of 

 surrounding white substance, and either naked or covered with a prolonga- 

 tion of the primitive sheath. But, apart from these pale continuations of 

 white fibres, there are nerve-fibres which exhibit the non-medullated charac- 

 ter throughout their whole length. These are the pale grey fibres first 

 pointed out by Remak, and commonly designated by his name, which are 

 found, with or without associated white fibres, chiefly in the sympathetic but 

 also in other nerves. The branches of the olfactory nerve of man and 

 mammalia consist wholly of these pale fibres. They were named gelatinous 

 (by Henle) from their aspect, not their chemical nature. They measure 

 from -g-J^th to ^^ ^th of an inch in diameter, appear flattened, translucent, 

 homogeneous, or very faintly granular, and sometimes finely striated longi- 

 tudinally. At short distances they bear oblong nuclei, which have been 

 supposed to belong to a sheath (Max. Schultze). As these fibres generally end 

 peripherally and some (olfactory) are known to begin centrally by a 



