370 



GENERAL STRUCTURE AND FUNCTIONS 



119 - 



gradually advances from the edges of the filament toward its 

 centre, until its entire thickness after a time presents the same 

 appearance. The effect of this process can also be seen in those 

 portions of the white substance which have been pressed out from 

 the interior of the filaments, and which float about in the form of 



drops. (Fig. 118, a.) These 

 drops are always covered 

 with a layer of coagulated 

 material which is thicker 

 and more opaque in propor- 

 tion to the length of time 

 which has elapsed since the 

 commencement of the alter- 

 ation. 



The nervous filaments 

 have essentially the same 

 structure in the brain and 

 spinal cord as in the nervous 

 trunks and branches ; only 

 they are of much smaller 

 size in the former than in 

 the latter situation. In the 

 nervous trunks and branches, 

 however, outside the cranial 

 and spinal cavities, there 

 exists, superaclded to the 



nervous filaments and interwoven with them, a large amount of 

 condensed areolar or fibrous tissue, which protects them from 

 injury, and gives to this portion of the nervous system a peculiar 

 density and resistance. This difference in consistency between the 

 white substance of the nerves and that of the brain and spinal cord 

 is owing, therefore, exclusively to the presence of ordinary fibrous 

 tissue in the nerves, while it is wanting in the brain and spinal 

 cord. The consistency of the nervous filaments themselves is the 

 same in each situation. 



The nervous filaments are arranged, in the nervous trunks and 

 branches, in a direction nearly parallel with each other. A certain 

 number of them are collected in the form of a bundle, which is 

 invested with a layer of fibrous tissue, in which run the small 

 bloodvessels, destined for the nutrition of the nerve. These pri- 

 mary bundles are again united into secondary, the secondary into 



NERVOUS FII.AM ENTS from sciatic nerve, showing 

 tbeir coagulation. At , th.) torn extremity of a 

 nervous filament with the axis cylinder (b) protruding 

 from it. At c, the white substance of Sch wann is nearly 

 separated by accidental compression, but the axis- 

 cylinder passes across the ruptured portion. The out- 

 line of the tubular membrane is also seen at c on the 

 outside of the nervous filament. 



