THE NERVOUS SYSTEM- PERINEURIUM. 265 



or less autonomous, and in a great measure independent 

 of one another. 



If in the first instance we exclude the ganglionic sub- 

 stance and confine ourselves simply to the fibrous matter, 

 we have on the one hand the real (peripheral) nerves in 

 the narrower sense of the word, and on the other the 

 large accumulations of white medullary substance, of which 

 the greater part of the cerebrum, cerebellum, and the 

 columns of the spinal marrow is composed. The fibres 

 of these different parts are indeed on the whole similarly 

 constructed, but disclose in their intimate structure such 

 numerous, and in part, such considerable differences, that 

 there are spots, with regard to which even at this very 

 moment we cannot say with certainty whether the ele- 

 ments we have before us are really nerves, or belong to 

 an altogether different kind of fibres. The greatest cer- 

 tainty has been acquired with regard to the structure of 

 the ordinary peripheral nerves ; in them the following 

 can generally be distinguished with tolerable facility. 



All the nerves which can be followed with the naked 

 eye contain a certain number of subdivisions, or fasci- 

 culi, which afterwards separate in the form of branches 

 or twigs. On tracing out these individual twigs which 

 keep continually dividing, we find that the nerve under 

 nearly all circumstances retains a fascicular arrangement 

 until nearly its ultimate divisions, so that every fascicu- 

 lus in its turn comprises a greater or less number of so- 

 called primitive fibres. The term, primitive fibre, which 

 is here employed, was originally selected, because a 

 nerve-fasciculus was regarded as analogous to the primi- 

 tive fasciculus of a muscle. This notion afterwards be- 

 came almost obsolete, and Robin was the first who in 

 more recent times again directed attention to the sub- 

 stance which holds the fasciculus together and which he 

 called perineurium. It consists of very dense connective 



