38 HABIT AND INTELLIGENCE. [chap. 



analysis of the facts of Mind has shown that there are 

 Three three primary mental functions : that is to say : — 



primary 



™®°*^^ Consciousness, or Feeling : 



Thought : and 

 Will. 



functions, 



probably It is at least a probable hypothesis, that the three sets 

 spondino- ^^ Cerebral nerves correspond to the three primary mental 

 thereto. functions. But how are the respective functions of the 

 three sets of nerves to be identified ? Here it is important 

 to remember, that although thought and will are usually 

 accompanied by consciousness, they are not always so : 

 there may be unconscious thought, and the facts of 

 somnambulism appear to show that there may be un- 

 conscious voluntary determinations. These facts greatly 

 Nerves of strengthen the probability that the nerves of conscious- 

 conscious- j^ggg^ ^^ least, are distinct from those of thought and will. 

 tiuct from Now, liow are we to identify the nerves of consciousness ? 

 thought It will be seen that of the three sets of cerebral nerves, 

 and will, r^g enumerated above, only one is in connexion with the 

 sensory ganglia, leading up from them to the ganglionic 

 substance of the cerebrum. Tlie functions of these nerves 

 must have something to do with the functions of the 

 sensory ganglia. But they are not nerves of sensation. 

 The nerves of sensation are those which are in connexion 

 with the external organs of sense. They may be, however. 

 Nerves of and I believe are, the nerves of consciousness : whether 

 conscious- ^YiQ primary consciousness of sensation, or the secondary 



ness, how r j ' j 



identified, consciousness of memory and thought. 



The same kind of reasoning applies to what I believe to 

 be the nerves of thought. The mass of the ganglionic 

 substance of the cerebrum, and of the fibres connecting 

 its different parts, varies as between different species of 

 animals and between different individuals among men, in 

 some kind of approximate proportion to their intellectual 

 powers ; and it is doubted by none that the cerebrum is 

 Thought is the organ of thought. Thought, as we have seen, is not 

 unco^u- necessarily conscious. That is to say, it is in itself uncon- 

 scious, scious, though it is usually accompanied by consciousness. 



