THE NERVOUS SYSTEM 325 



root. The diameter of the fibres which go to the viscera is 

 not more than one-fifth as great as that of the other fibres of 

 an anterior root. Similar slender fibres are found hi the vagus 

 nerve. If all organs are removed from an animal's chest and 

 abdomen, a string of small pearl-like ganglia, united by a 

 longitudinal cord, is seen lying on either side of the bodies of the 

 vertebrae, one ganglion for each segment. This string of ganglia 

 is termed the " sympathetic chain " (cf. p. 243). The small 

 medullated fibres of the anterior spinal roots join these ganglia. 

 Some of them arborize about their cells ; some pass by them to 

 arborize in ganglia which lie farther afield, on the course of the 

 great bloodvessels and within the viscera. The axons of neu- 

 rones whose cell-bodies are within a ganglion break up into 

 bunches of non-medullated fibres. In this way the fibres of 

 the sympathetic system are increased in number. Each of its 

 neurones is a multiplying and distributing station. There is no 

 evidence that it in any way serves as a " centre," takes part in 

 reflex action, or otherwise usurps the functions of the grey matter 

 of the spinal cord. Nerve-cells are thickly strewn between the 

 mucous membrane and the muscular coat, and again between 

 the two layers of the muscular coat of the alimentary canal. 

 It is not so certain that this system has no " central " functions. 

 The remarkable degree in which the wall of the intestines re- 

 tains its capacity for co-ordinated movement, after all nerves 

 which reach it from the ganglia and through the vagus have 

 been cut, suggests that the plexus of nerves within it does act 

 to some extent as a reflex centre. If we leave the case of the 

 intrinsic nervous system of the alimentary canal open, awaiting 

 further proof, there is no reason for looking upon the sympa- 

 thetic system as in any degree independent of the spinal cord 

 and brain. It does its work on a large scale, and its work is of a 

 low order. Nature does not need to connect up the viscera and 

 bloodvessels with the central nervous system by means of 

 fibres as thick as those used for skeletal muscles. It is more 

 convenient to provide for the multiplication of the nerves 

 which must be extremely numerous, owing to the relatively 

 minute size of the muscle-fibres for which they are destined 

 outside the central system than it would be to include the 

 necessary distributive cells within it. Again, we find that a 

 nerve-cell, when we see it at close quarters, shows no evidence 



