NERVOUS SYSTEM OF VERTEBRATES. 



CHAPTER I. 

 THE STUDY OF THE NERVOUS SYSTEM. 



The nervous system is a complex system of organs which stands 

 in close relations with all the other organs of the body. The study 

 of the nervous system requires on the one hand an examination 

 of the structure and mode of functioning of its component parts 

 and on the other a consideration of its manifold relations to other 

 organs. There must be considered (a) structural connections 

 which provide for the reception and discharge of nerve impulses 

 which play an essential part in the functioning of organs and in 

 the correlation of their activities; and (b) the more general 

 relations of place, the arrangement of nervous and other organs 

 in the body. In both these respects the actual relations of the 

 nervous system in the organism have been determined by the 

 conditions and course of the evolution of the vertebrate organism, 

 in which the adaptation of structure to the mode of life is the 

 controlling principle; and by the conditions of embryonic develop- 

 ment, in which special structures adapted to the embryonic mode 

 of life and inherited structures adapted to ancestral modes of 

 life play important parts. The student who wishes to gain a 

 knowledge of the nervous system is of necessity thrown into this 

 maze of complicated relationships, but fortunately he finds 

 methods of investigation adapted to the problems to be solved. 



While the student may direct his attention especially to the phase 

 of structure or the phase of function, he should understand from 

 the outset that great progress and permanent results are to be 

 attained only when the study of structure and the study of function 

 go hand in hand. While in general the detailed study of structure 

 must precede the detailed study of function, the interpretation 



