CHAP, in.] GENERAL FEATURES OF NERVOUS TISSUES. 173 



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. 



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/u, 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 

 inner side are smaller. A quantity of connective tissue carrying 

 blood vessels and lymphatics runs between the groups and passing 

 into each group runs between the cells and fibres ; and a thick 

 wrapping of connective tissue continuous with the sheath of the 

 nerve surrounds and forms a sheath for the whole ganglion. 



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

 examined under a higher power, either after having been isolated 

 or in an adequately thin and prepared section, will present the 

 following features. 



The cell consists of a cell body which is, normally, pear-shaped, 

 having a broad end in which is placed the nucleus and a narrow 

 end which thins out into a stalk and is eventually continued 



