GENERAL STRUCTURE OF THE NERVOUS SYSTEM. 357 



FlQ. 92. 



directions. At a certain distance from their origin, the processes are 

 often branched, the branches again dividing and subdividing until 

 reduced to a ramification of slender filaments. But in many instances, 

 on the other hand, the cell-process extends for a considerable distance 

 without division, as a nearly cylindrical or flattened filament, similar 

 in appearance to the axis cylinder of a nerve fibre. 



Each nerve cell, in its normal situation, is contained in a sheath or 

 capsule, consisting of a thin, colorless, homogeneous membrane, with 

 oval nuclei on its inner surface. In the fresh condition, the cell nearly 

 fills the cavity of its capsule ; but in preparations obtained with hard- 

 ening fluids there is usually more or less shrinkage or condensation of 

 the cell substance, so that 

 it appears surrounded by 

 a vacant space, limited by 

 the inner surface of the 

 capsule (Fig. 92). The 

 cell-process, as it emerges, 

 is accompanied by a tubu- 

 lar prolongation of the 

 capsule, in which it lies 

 enclosed. 



Connection between 

 Nerve Fibres and Nerc<> 

 Cells. In all cases the 

 nerve fibres are connected 

 at their central origin with 

 deposits of gray substance, 

 into which they penetrate 

 and in which they pursue 

 an intricate course be- 

 tween its nerve cells. It 

 is very difficult to distin- 

 guish the final connection 

 of the two ; since in the 

 dilaceration of fresh speci- 

 mens, both the fibres and 

 the cell-processes are easily torn off; and in transparent sections of 

 hardened specimens, a nerve fibre seldom follows the exact plane of the 

 section for any considerable distance. But by a combination of both 

 methods it has been shown that the nerve fibre is in many cases a con- 

 tinuation of the cell-process, and this continuity is so frequently visible 

 that it may be regarded as the normal mode of connection between 

 nerve fibres and nerve cells. 



This connection is often extremely probable, in the spinal ganglia 

 of man and mammalia, from the appearance of the cell-process, which 

 soon after its origin resembles so completely an ordinary axis cylinder 

 that there is no perceptible difference between them. It is rendered 





NERVE CELLS, from spinal and sympathetic ganglia of 

 man, enclosed in their eapsular sheaths. From hardened 

 preparations. (Key and Retzius.) 



