GENERAL FEATURES OF NERVOUS TISSUES. 125 



plied by somatic nerves, after running for some distance in the splanchnic 

 division ( F), turn aside (r. v and v. m) and join the somatic division, the 

 fibres of which they accompany on their way to the tissues whose bloodvessels 

 (in'~) they supply. 



We have seen ( 68) that a nerve going to a muscle is composed of nerve 

 fibres, chiefly medullated, some, however, being non-medullated, bound 

 together by connective tissues. The same description holds good for the 

 whole somatic division of each of the spinal nerves. The splanchnic division 

 also consists of medullated and non-medullated fibres bound together by con- 

 nective tissue, but in it the nou-medullated fibres preponderate, some branches 

 appearing to contain hardly any medullated fibres at all. The non-medul- 

 lated 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 ner- 

 vous 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 and 

 occasionally along the course of spinal 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 situations. 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. 



93. 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 conspicuously 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//., 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 gang- 

 lion, and that the racemose groups on the inner side are smaller. A quantity 

 )f connective tissue carrying bloodvessels and lymphatics runs between the 

 roups, and passing into each group runs between the cells and fibres ; and 

 thick wrapping of connective tissue continuous with the sheath of the 

 icrves surrounds and forms a sheath for the whole ganglion. 



Each of the nerve cells ganglionic cells, as they are called examined 



