ITS HISTOLOGICAL RELATIONS. 99 



of nearly concentric membranes, measure from 0*5 to 2'0"', and 

 a nerve-fibre terminates in each of them. These concentric mem- 

 branes are composed of connective tissue, arid between the coats 

 there is a serous fluid, which collects in larger quantities in the 

 narrow, long, central space of these Pacinian bodies. Each of 

 these corpuscles is attached to the nerve to which it belongs by 

 means of a short pedicle, which is formed by layers of the connec- 

 tive tissue of the bodies, and by the neurolemrna; through this 

 pedicle an animal nerve-fibre proceeds from the nerve, and extend- 

 ing to the central cavity of the corpuscle, diminishes rapidly until 

 it resembles the axis-cylinder. It traverses the narrow central 

 space, and, after splitting into two or three parts, terminates 

 opposite its point of entrance in fine nodules. 



In the nervous system, and more especially in the central 

 organs, as the brain, the spinal cord, and the ganglia of the spinal 

 nerves and of the sympathetic, there occur, in addition to the 

 fibres, peculiar cells, termed the nerve-cells, (accessory corpuscles, 

 or ganglionic globules). These bodies are true cells, consisting of 

 an investing membrane, a nucleus with one or more nucleoli, and 

 soft contents interspersed with molecular granules. The size of 

 these nerve-cells is as various as the diameter of the nerve-tubes, 

 and they may be divided into large and small, as we divide the 

 nerve-tubes into thick and thin. The smaller nerve-cells occur 

 principally in the ganglia of the sympathetic, and the larger ones in 

 company with the double-outlined fibres of the cerebro-spinai 

 nervous system; but this rule is not without many exceptions. 

 The diameter of the larger nerve-cells is about 0*05 or 0*06'", 

 whilst that of the smaller cells is. frequently not more than 0*002 

 or 0-003'" (Kolliker). 



These cells vary in form no less than in size. Large, almost 

 spherical or oval cells occur principally in the grey substance of 

 the brain and spinal cord. Fusiform, trapezoidal, irregularly tri- 

 angular nerve-cells, provided with numerous, and often ramifying 

 processes, abound in the grey substance of the central organs. 

 We find in the ganglia of the sympathetic scarcely any cells which 

 have not one or two pale processes. Many of the nerve-fibres 

 take their origin from these cells, and we often see one, and not 

 unfrequently two fibres proceeding from a single cell. 



The nerve-cells are covered externally by a structureless mem- 

 brane, which is in some cases extremely thin and scarcely visible, 

 and in others somewhat thicker and easy of recognition. The 

 cells which have thin walls occur more especially in the central 



II 2 



