CHAP, ii.] 



THE BRAIX. 



761 



ing from one to the other, an increase in prominence and in 

 differentiation of the motor region accompanied by an increase 

 in the bulk of the pyramidal tract ; among the many striking 

 differences between the brains of these several animals, these two 

 features, the increasing complexity of the motor region, and the 

 increasing size of the pyramidal tract, are among the most strik- 

 ing. The size of the pyramidal tract is itself correlated to the 

 complexity of the motor region, and, being the more easily 

 determined, may be used as indicating both ; the difference in 

 the size of the pyramidal tract in these animals is seen all along 

 the whole length of the cord (Fig. 133). Now as regards mere 

 quantity of movement, if we may use such an expression, the 

 differences between these animals are of no great moment. If 

 we were to take the amount of energy expended as movement 

 in twenty-four hours per gramme of muscle present in the body 

 in each of the four cases, we should certainly not find any cor- 



MAN 



MONKEY 



DOC 



FIG. 133. DIAGRAM TO ILLUSTRATE THE RELATIVE SIZE OF 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' in 

 Fig. 114 ; 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 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 grey matter seems relatively large in C because the section was taken from 

 a very young puppy. 



respondence between that and the size of the pyramidal tract. 

 If however we take a particular kind of movement, what we may 

 perhaps call skilled movement, that is movement carried 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 motor 

 region is in some way especially concerned with the kind of 

 movement which we have called 4 skilled.' 



