THE SYMPATHETIC SYSTEM OF NERVES. 539 



except that in the cerebro-spinal system the nerve cells are 

 accumulated into large masses, and the connections between 

 the several segments are effected by fibres which do not stray 

 from the region of the central organ, and which preserve the 

 character of the central fibres, whilst in the sympathetic the 

 cells are more separated, and their connections, both amongst 

 themselves and with the cells of the cerebro-spinal system, are 

 established by peripheric nerve fibres. In the cerebro-spinal 

 medullary system the principle of the centralisation of the 

 elements is represented, whilst in the sympathetic system it 

 is rather decentralisation which is the essential feature. 



The medullary substance of the sympathetic, like that of 

 the brain and spinal cord, is composed of cells and fibres, and 

 in both situations the fibres arise from the cells. 



The peculiarities distinguishing these two elements of the 

 sympathetic nervous system will here be carefully considered ; 

 whilst, for their general characters, the reader is referred to 

 the third chapter of this work. 



The ganglion cells of the sympathetic are partly united 

 into large groups, to form the so-called ganglia or nerve- 

 knots, and are partly intercalated in the course of the nerve 

 trunks, or are distributed in a scattered manner in the various 

 organs. 



The nerve-knots or ganglia of the sympathetic are provided 

 with an investing sheath of connective tissue, which gives off 

 processes that penetrate between the several cells, and form as 

 it were a separate capsule to each. The connective tissue con- 

 sequently constitutes a trellis-work, the interspaces of which 

 contain the nerve cells ; it at the same time supports the 

 bloodvessels. Each ganglion possesses an afferent and an 

 efferent nerve, the fibres of which pursue various courses 

 within the ganglion, one portion running from the periphery 

 to the cerebro-spinal centre, and another in the opposite direc- 

 tion, though as yet no characteristic mark has been discovered 

 by which the one can be distinguished from the other. The 

 nerve cells are imbedded in a confused mass of fibres, so that 

 an insight into the mode of connection between the cells and 

 fibres can only be obtained from careful investigation. Cells 

 are often met with distributed in the course of the smaller 



