ON VOLUNTARY MOVEMENTS. 



673 



we should certainly not find any correspondence between that and the size 

 of the pyramidal tract. If, however, we take a particular kind of move- 

 ment, what we may perhaps call skilled movement, that is, movement car- 

 ried out by means of intricate changes in the central nervous system, we do 

 find a remarkable parallelism in the above cases between the amount of such 

 skilled movement entering into the daily life of the individual and the size 

 of the pyramidal tract. In these two respects man is much above the monkey, 

 and the monkey far above the dog. We may conclude then that the cortical 



FIG. 151. 



MAN 



MONKEY 



DOG 



Diagram to illustrate the Relative Size of the Pyramidal Tract in the Dog, Monkey, and Man. 

 (Sherrington.) The figure shows in outline the lateral half of the cord, at the level of the fifth 

 thoracic nerve, in A, man ; B, monkey ; C, dog. A is a reproduction of IP in Fig. 127 ; B and C 

 are drawn of the same size as A. Py., shaded obliquely, the pyramidal tract ; the depth of shad- 

 ing indicates that the tract is more crowded with true pyramidal fibres as well as larger in A 

 than in B, and in B than in C. In B, Py' is an outlying portion of the pyramidal tract separated 

 from the rest by the cerebellar tract; Py. d., the direct pyramidal tract, present in man only. 

 The gray matter seems relatively large in C because the section was taken from a very young 

 puppy. 



motor region is in some way especially concerned with the kind of movement 

 which we have called " skilled." 



571. These skilled movements are, to a large extent, though not 

 exclusively, voluntary movements. We have, in a previous section, seen 

 reason to believe that the cerebral cortex is in some way especially asso- 

 ciated with the development of voluntary movements. Putting together 

 this conclusion and the conclusions just arrived at, we are naturally led to 

 the further conclusion that the cortical motor region, with the pyramidal 

 tract belonging to it, plays an important part in carrying out voluntary 

 movements. Do other facts support this view ; and if so, what light do 

 they throw on the question as to what part and what kind of part the 

 motor region thus plays ? 



In this connection we naturally desire to know what are the results of 

 removing from an otherwise intact animal the whole motor region and more 

 especially this or that particular portion of it. Before proceeding further, 

 however, we may once more call attention to the caution given in 495 and 

 repeated in 553 ; indeed, when we consider the high organization and com- 

 plex functions which obviously belong to the cortex, when we bear in mind 

 that it appears to govern, and must therefore be bound by close ties to almost 

 all the rest of the central nervous system, we must be prepared to find after 

 removing a portion of cortex that the pure " deficiency" phenomena, those 

 which result from the mere absence of a piece of the cortex, are largely 

 obscured by the other effects of the operation. 



In the rabbit the results have been almost purely negative. When in this 

 animal the part of the cortex which may be considered as the motor region 



43 



