CHAP, in.] GENERAL FEATURES OF NERVOUS TISSUES. 175 



dullated and non-medullated fibres bound together by connective 

 tissue, but in it, as a whole, the non-medullated fibres preponderate, 

 some branches appearing to contain hardly any medullated fibres 

 at all. The non-medullated fibres which are found in the somatic 

 division appear to be fibres which have joined that division from 

 the splanchnic division. So prominent are non-medullated fibres 

 in splanchnic nerves and hence in the sympathetic system~that 

 they are sometimes, called sympathetic fibres. 



We have said that the axis-cylinder, whether of a medullated 

 or non-medullated fibre, is to be considered as a long drawn out 

 process of a nerve cell. Nerve cells are found in three main 

 situations. 1. In the central nervous system, the brain and 

 spinal cord. 2. In the several ganglia placed along the course of 

 the nerves, both the spinal ganglia, and the ganglia of the 

 splanchnic or sympathetic system. 3. At the terminations of 

 nerves in certain tissues. Some of these latter are to be regarded 

 as small, more or less terminal, ganglia, and similar minute 

 ganglia consisting of two or three cells only are found frequently 

 along the course of splanchnic nerves ; such cells really therefore 

 belong to the second group. But besides this, in certain situations, 

 as for instance in certain organs of the skin, and in the organs of 

 special sense, nerves, generally afferent or sensory in nature, either 

 actually end in, or at their termination are connected with, cells 

 which appear to be of a nervous nature ; such cells form a distinct 

 category by themselves. 



Hence along its whole course a nerve consists exclusively of 

 nerve fibres (and the connective tissue supporting them), except in 

 the central nervous system from which it springs, in the ganglia, 

 great and small, through which it passes or which are attached to 

 it at one part or another of its course, in both of which situations 

 nerve cells are found, and at its termination where its fibres may 

 end in nerve cells. 



The features of these nerve cells differ in these several situa- 

 tions. The characters of the terminal cells which, as we have 

 said, are chiefly sensory, and the structure of the brain and spinal 

 cord we shall study in detail later on. We may here confine our 

 attention to the nerve cells of the ganglia, and to some of the 

 broad features of the nerve cells of the spinal cord. 



97. Spinal ganglia. When a longitudinal section of a spinal 

 ganglion is examined under a low power, the fibres of the posterior 

 root as they enter the ganglion are observed to spread out and 

 pass between relatively large and conspicuous nucleated cells 

 which are to a large extent arranged in groups, somewhat after the 

 fashion of a bunch of grapes. These are the nerve cells; they 

 have frequently a diameter of about 100 /A but may be still larger 

 or may be much smaller. In a transverse section it will be 

 observed that a large compact mass of these cells lies on the 

 outer side of the ganglion, and that the racemose groups on the 



