CHAPTER XII 

 THE CENTRAL NERVOUS 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 pro- 

 cesses have bulked more largely in our pages than the anatomy 

 and histology of the tissues themselves. 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 place 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 

 probability, 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 fundamental distinc- 

 tion 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. 



I. Structure of the Central Nervous System. 



In unravelling the complex structure of the central nervous 

 system, we avail ourselves of information derived (i) from its 

 gross anatomy ; (2) from its microscopical anatomy ; (3) from 

 its development ; (4) from what we may call, although the term 

 is open to the criticism of cross-division, its physiological and 

 pathological anatomy. 



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