CHAPTER XII. 

 THE CENTRAL NE3.VOUS SYSTEM. 



IN other divisions of our subject we have been able to 

 follow to a greater or less extent the processes which take 

 place in the organs described. The chemistry and the 

 physics of these processes have bulked more largely in our 

 pages than the anatomy and histology of the tissues them- 

 selves. In dealing with the central nervous system we must 

 adopt a method the very reverse of this. Its anatomical 

 arrangement is excessively intricate. The events which 

 take [lace in that tangle of fibre, cell, and fibril are, on the 

 other hand, almost unknown. So that in the description of 

 the physiology of the central nervous system we can as yet 

 do little more than trace the paths by which impulses may 

 pass between one portion of the system and another, and from 

 the anatomical connections deduce, with more or less pro- 

 bability, the nature of the physiological nexus which its 

 parts form with each other and the rest of the body. And 

 here it may be well to remark that, although for convenience 

 of treatment we have considered the general properties of 

 nerves in a separate chapter, there is not only no funda- 

 mental distinction between the central nervous system and 

 the outrunners which connect it with the periphery, but 

 obviously a central nervous system would be meaningless 

 and useless without afferent nerves to carry information to 

 it from the outside, and efferent nerves along which its 

 commands may be conducted to the peripheral organs. 



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