THE MACHINERY OF COORDINATED MOVEMENTS. 643 



Our knowledge is largely confined to the experience that when in a dog the 

 cerebral convolutions are removed piecemeal at several operations, the 

 animal may be kept alive and in good health for a long time, many months 

 at least, even after these parts of the brain have been reduced to very small 

 dimensions, and that under these circumstances the animal is not only able 

 to carry out with some limitations his ordinary bodily movements, but also 

 exhibits a spontaneity obviously betokening the possession not merely of a 

 conscious volition but of a certain amount of intelligence. Unless we are 

 willing to believe that a mere fragment, so to speak, of the hemispheres can 

 take on most extended powers, such an experience seems to show that in the 

 dog as in the rabbit and in the bird, the development of so-called higher 

 functions is not limited to the cerebral hemispheres, that the middle and 

 lower portions of the brain in the higher animals as compared with the 

 lower do not increase in bulk merely as the instruments of the hemispheres, 

 but like the hemispheres acquire more and more complex functions. We 

 may perhaps go so far as to ask the question whether the volition and intel- 

 ligence which such a dog exhibits is not as much the product of the parts 

 lying behind the hemispheres as of the stump left in the front. 



If we can thus say little about the condition of a dog without the cerebral 

 hemispheres, we can say still less about the monkey, which in all matters 

 touching the cerebral nervous system serves as our best, indeed our only 

 guide for drawing inferences concerning man ; but in all probability the 

 monkey in this respect bears somewhat the same relation to the dog that the 

 dog bears to the bird. 



In short, the more we study the phenomena exhibited by animals pos- 

 sessing a part only of their brain, the closer we are pushed to the conclusion 

 that no sharp line can be drawn between volition and the lack of volition, 

 or between the possession and absence of intelligence. Between the muscle- 

 nerve preparation at the one limit and our conscious willing selves at the 

 other there is a continuous gradation without a break ; we cannot fix on 

 any linear barrier in the brain or in the general nervous system, and say, 

 " Beyond this there is volition and intelligence, but up to this there is none." 



This, however, is not the question with which we are now dealing. What 

 we want to point out is that in the higher animals, including at least some 

 mammals, as in the frog, after the removal of the cerebral hemispheres, even 

 though conscious volition and intelligence appear to be largely, if not en- 

 tirely lost, the body is still capable of executing all the ordinary movements 

 which the animal in its natural life is wont to perform, in spite of these 

 movements necessitating the cooperation of various afferent impulses ; and 

 that therefore the nervous machinery for the execution of these movements 

 lies in some part of the brain other than the cerebral hemispheres. We 

 have reason for thinking that it is situated in the structures forming the 

 middle- and hind-brain ; as we shall see, interference with these parts pro- 

 duces at once remarkable disorders of movement. 



THE MACHINERY OF COORDINATED MOVEMENTS. 



555. We may now direct our attention for a while to some considerations 

 concerning the nature of this complex nervous machinery for the coordina- 

 tion of bodily movements, and especially concerning the part played by 

 afferent impulses. Most of our knowledge on this point has been gained 

 by a study of animals not deprived of, but still possessing, their cerebral 

 hemispheres, or by deductions from the data of our own experience ; but it 

 is possible in most cases to eliminate from the total results the phenomena 

 which are due to the working of a conscious intelligence. Some of the most 



