THE PHYSIOLOGY OF THE BRAIN. 627 



antecedent nerve processes arousing its activity would be 

 quite different in the two cases; and they would yet again be 

 different if I clenched the fist in order to explain to a child 

 the meaning of the word clench. We see then that the im- 

 mediate motor centres may be excited in various ways and in 

 various combinations quite apart from the cortex of the cere- 

 brum and by fibres not connected with the pyramidal tracts; 

 and that when excited from the cortical area of the cere- 

 brum through fibres of the pyramidal tract, that area itself 

 may be excited or controlled in its activity by a vast number 

 of other parts of the cortex, and by non-cortical parts of the 

 nervous system. The motor area cannot properly be spoken 

 of as the seat of volition : an act of willing is the final out- 

 come of changes in other and often numerous other regions 

 of the cortex, the resultant of whose material processes is a 

 discharge of efferent impulses from some region of the motor 

 area. 



The permanent effects of local lesions of the Rolandic 

 region differ with the development of the brain. In dogs 

 removal of the left brain region connected with the fore 

 paw causes only temporary motor paralysis of the limb on 

 the other side; after a time the animal learns to walk again 

 as well as before: then removal of the corresponding area on 

 the right side of the brain is followed by paralysis of both fore 

 limbs. This has been supposed to show that the centre on 

 the right side had taken up the duty of control for both sides 

 after that on the left had been removed. However that may 

 be, the second paralysis is also only temporary, disappearing 

 in some weeks or months; and as has been already stated, 

 even after removal of all the motor area the animal occasion- 

 ally learns in the course of time to walk nearly as well as 

 ever. This must be due to lower centres (corpora striata ?), 

 and the question is whether the movements in such cases are 

 truly volitional, for definite acts of willing a movement prob- 

 ably play a very small part in a dog's life: most of its move- 

 ments are the immediate efferent expression of afferent im- 

 pulses and true volitions have but a small part in them. In 

 the lower monkeys definite motor effects of removal of part 

 of the cortical motor area are also temporary, but last longer 

 than in dogs; and in the anthropoid apes the same is the case 

 in a greater degree, and according to some experimenters 

 certain delicate combined movements are permanently lost 



