270 Professor E, A. Schdfer [March 20, 



accustomed to associate with conscious sensation. It is, in fact, one of 

 the most difficult problems in physiological psychology to differen- 

 tiate in all cases between these forms of movement ; although in 

 many instances the distinction is evident enough. Many actions lie 

 on the borderland, and, to include these, psychologists have invented 

 the term " psychical reflex," by which they mean a kind of action 

 which in a measure partakes of the nature of a purely reflex action, 

 but which is nevertheless set going as the result of consciousness. 

 But since it must be admitted that every voluntary action, however 

 spontaneous it may appear, is the result of antecedent impressions 

 which have reached the brain by sensory paths, the distinction 

 between a psychical reflex and a volitional act is one not easily 

 maintained. There is no doubt that volitional impulses originate 

 in and emanate from the cortex of the brain. But when we use the 

 word originate, we must be careful to remember that no such im- 

 pulse would ever emanate from the cerebral cortex unless sensory 

 impulses of one kind or another had at some time previously been 

 communicated to that cortex. It is only in this sense that we can 

 speak of a voluntary impulse as originating in the brain. In many- 

 cases it is quite obvious that this is not their real origin. If I, 

 for example, receive a slap in the face, my immediate impulse is 

 to return the blow with interest, and this would probably be termed 

 a " psychical reflex," but if the circumstances are such that it is 

 impossible at the moment to perform that action, which has obviously 

 been started by the sensory impression which I have received, this 

 impression is stored for a while within the grey matter of the brain, 

 to be brought out at a convenient opportunity and converted into the 

 "volitional impulses" which will enable me to effect my purpose. 

 In the one case, as in the other, the movement is called into play by 

 the same sensory impulse as originally reached the brain. What we 

 call volition is, as a matter of certainty, the resultant of sensory 

 impressions which have been previous received, and which may or 

 may not have been stored for a long time within the cerebral grey 

 matter. The part of that grey matter from which they emanate is 

 at the present day fairly well known. The observations on cortical 

 localisation which were begun by Fritsch and Hitzig in 1870, and 

 brilliantly continued by Ferrier some three years later, have been 

 of late years extended still further, both by clinical observations 

 upon the human subject and by the work of many experimentalists. 

 As a result of the most recent investigations, those of Professor 

 Sherrington and Dr. Griinbaum upon the brain of the chimpanzee, it 

 has been made clear that it is from the j^art of the cerebral cortex 

 which lies immediately in front of the Assure of Rolando that im- 

 pulses for the volitional movement of all parts of the body emanate. 

 The problem that I propose to put before you this evening is, the 

 consideration of the paths which are followed within the nerve centres 

 by these volitional impulses, in the passage from the grey cortical 

 layer of this part of the cerebrum to the grey matter of the spinal 



