CHAP, ix.] NERVOUS SYSTEM AND ORGANS OF SENSE. 255 



at other parts of its course than at their origins or terminations. The 

 terminations of nerves, whether they end peripherally or centrally, are 

 often spoken of as " end organs." White nerve-fibres run side by 

 side in a bundle, bound together by delicate connective tissue, which 

 also forms a sheath for them called the neurilcmma. In spite of 

 their close proximity these fibres have never been observed to 

 anastomose, nor have single fibres been seen to branch till within a 

 microscopic distance of their termination. This ultimate branching 

 may be due to the axis cylinder really consisting of distinct fibrils 

 bound together, as a longitudinal striated appearance they sometimes 

 exhibit would seem to indicate. On the other hand, by the action 

 of nitrate of silver they may be made to exhibit a transverse striation 

 like that of muscular fibres, so that the meaning of either of these 

 appearances is problematical.* 



The grey or pale fibres are chiefly found in the nerves of the 

 sympathetic system, but the olfactory nerves also are entirely com- 

 posed of them. They are from -^-oVo- to THMMT f an i nc ^ i* 1 diameter, 

 and are devoid of that apparent distinctness of parts characterising 



Fig. 122. XERVE-CELLS FROM THE OUTER GREY PORTION OF THE CEREBELLUM, MAGNIFIED 



2(30 DIAMETERS. 



. Cells, each containing a nucleus, with a 



distinct nucleolus. 

 b &. Simple unbranched processes. 



cc', dd'. Branches radiating in different direc- 

 tions, and ramifying in various degrees. 



the white fibres. They appear translucent, homogeneous, and slightly 

 granular, and exhibit at intervals oblong nuclei, which have been 

 supposed to belong to the sheaths of such nerves. 



Nerve cells, or nerre corpuscles, are very different in appearance 

 from nerve fibres. Each consists of a round, oval, pyramidal, club- 

 shaped, pear-shaped, or many-cornered microscopic body, formed of 

 protoplasm, and which may appear clear or granular according to cir- 

 cumstances (perhaps of observation), and which contains a nucleus 

 with one or more nucleoli. Some of these cells are devoid of processes 



* There now appears to be reason to suppose that the axis cylinder is really 

 segmented. 



