DR. HILL, FROM REFLEX ACTION TO VOLITION. 39 



another of actions which, in their pronounced forms, we 

 distinguish as reflex and voluntary respectively. 



Much light is thrown upon this subject by a study of the 

 tissue, the "grey matter" of the central nervous system, in 

 which these actions are carried out. 



It belongs to two great divisions : — (1) The grey matter 

 of the spinal cord and of the central canal of the brain ; and 

 (2) the grey matter which covers the surface of the brain. 

 The former is the earlier or more primitive formation, the 

 latter appears much later in the animal series, and only 

 reaches a considerable development in its higher members. 

 The structure of the two is however fundamentally similar. 

 Each consists of a network into which afferent or sensory 

 nerves pour their impulses, and out of which efferent or motor 

 nerves take their start. The filaments of the network are 

 the ramifying processes of cells. Most of the cells are small, 

 but those which support motor nerve-fibres are large ; the 

 reason being, apparently, that the long nerve fibre, which 

 runs perhaps to a distant muscle, derives its nourishment from 

 the cell out of which it grows. Time would fail me to give 

 an account of the constitution of this network, nor am I for 

 another reason sorry to pass it by with a hasty notice, for it 

 happens that during the last year or two entirely new views 

 as to its constitution in detail have been advanced, and are 

 still sub judice. 



The only marked difference between the grey matter of 

 the brain and that of the spinal cord which we can point out 

 is that whereas the spinal cord receives sensory nerves and 

 gives origin to motor ones, the cortex of the brain is, so far 

 as we know, connected with the periphery only through the 

 mediation of the central grey matter, or plexus of the 

 spinal cord. 



These are the only points with regard to the evolution 

 and anatomy of the nervous system of which I wish to make 

 use for the purposes of my argument. 1st. It is formed 

 from the surface of the body. 2nd. It is in the first instance 

 intimately connected with the sense organs. 3rd. That it 

 consists of a plexus by means of which the cells of the sense 

 organs are placed in connection with muscle fibres. 4th. 

 That in the lowest animals it is the function of this network 

 to transfer sensory impressions to the appropriate motor 

 mechanism. 5th. That in higher animals the direct and inevi- 

 table transfer of impulses gives way to a greater or less 

 extent to the power of choice. 



