CHAP, ii.] 



THE BRAIN. 



1049 



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 moftkey, and the monkey far above 



MAN 



MONKEY 



DOG 



FIG. 128. 



DIAGRAM TO ILLUSTRATE THE RELATIVE SIZE or THE PYRAMIDAL TRACT 

 IN THE DOG, MONKEY AND MAN. (Sherrington. ) 



The figure shews 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 D 5 in 

 Fig. 104; B and C are drawn of the same size as A. Py., shaded obliquely, 

 the pyramidal tract ; the depth of shading 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 G. 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 grey matter seems relatively large in G because the section 

 was taken from a very young puppy. 



the dog. We may conclude then that the cortical motor region is 

 in some way especially concerned with the kind of movement 

 which we have called 'skilled.' 



658. 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 associated 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 582, and repeated in 640 ; 

 indeed when we consider the high organisation and complex 

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



