626 THE HUMAN BODY. 



cerebellum come into action also; take a man preparing for a 

 high jump: as he crouches and puts himself in bal/nce for 

 the spring he clenches his fists, quite unconsciously of course. 

 Here the immediate clenching centre is thrown into activity 

 along with the muscles of breathing, and of all parts of the 

 trunk and limbs. Each subsidiary peripheral centre plays its 

 part and the instreaming afferent impulses from the skin of the 

 feet, from the fibres of the muscular sense, from the semicir- 

 cular canals, from the eyes, are all concerned (without the 

 person's perception of them) in throwing the motor mechanisms 

 of midbrain, cerebellum, medulla, and cord into harmonious 

 activity, so that when the jump is actually willed it shall be 

 accomplished. But that in this case the volition plays a very 

 secondary part is obvious; it merely acts on an apparatus all 

 ready to discharge in a given way when a suitable additional 

 nerve impulse reaches it. A runner all tense for the start of 

 a hundred-yard race can hardly be said to start voluntarily 

 when he hears the signal; the case is comparable more to the 

 self-balancing of a pigeon deprived of its cerebral hemi- 

 spheres, when its perch is tilted. Next, suppose I clench my 

 fist "involuntarily," as we commonly say, when I see some- 

 thing that arouses my indignation; here clearly a mental 

 element is in play, but not a volitional one, and so far as 

 the movement is concerned probably the motor area of the 

 cortex has little or nothing to do with it: it is more in accord 

 with what is seen on animals to suppose that such simple 

 emotions and their characteristic movements may be carried 

 out by nerve apparatuses lying no higher than the thalami 

 and -corpora striata. If, however, I strike a man with the 

 intention to punish him, there can be little doubt that the 

 "clenching" centre is excited by fibres from the cortex and 

 passing down in the pyramidal tract. But this cortical area 

 may in turn be thrown into activity and may have its ten- 

 dency to discharge modified in many ways. My anger may 

 be the culminating result of many long past received and 

 interpreted and remembered sensations, and whether I shall 

 give the blow or restrain myself also be dependent on many 

 antecedents of experience. Again, I clench my hand to 

 knock doAvn a madman, as the only immediate method of 

 preventing him from committing a murder: here the same 

 motor cortical area no doubt would be thrown in action as 

 when the blow was struck in anger, but it is clear that the 



