686 THE BRAIN. 



exclusively the channel of volitional impulses in man than in such lower 

 animals, but also, bearing in mind the discussion in a previous chapter 

 ( 504) concerning the activities of the spinal cord of man, that the potential 

 alternatives presented by the spinal cord of the dog are greatly reduced in 

 that of man. And such clinical histories of disease or accidental injury in 

 man as we possess support this conclusion. Lesions confined to one-half of 

 the cord, or even lesions confined to the lateral column of one-half, appear 

 to lead to loss of voluntary power on the same side, and the same side only, 

 in the parts below the level of the lesion ; and the same symptoms have been 

 observed to accompany disease limited apparently to the pyramidal tract of 

 one side. Moreover, though cases of recovery of power have been recorded, 

 we have not such satisfactory evidence as in animals of the volitional im- 

 pulses ultimately making their way along an alternative route ; but here the 

 same doubts may be entertained as were expressed in discussing the reflex 

 acts of the cord in man. 



When we say that the loss of voluntary power is seen on the side of the 

 lesion only, we should add that this statement appears to apply chiefly to the 

 thoracic and lower parts of the cord. We have seen that in man, in the 

 upper regions of the cord, the pyramidal tract is only partly crossed ; a vari- 

 able but not inconsiderable number of the pyramidal fibres do not cross at 

 the decussation of pyramids, but running straight down as the direct pyram- 

 idal tract effect their crossing lower down in the cervical and upper thoracic 

 regions. Hence, we should infer that a hemisection of, or a lesion confined 

 to one side of, the cervical cord would affect the voluntary movements of the 

 crossed side as well as of the same side, though not to the same extent. But 

 we have no exact information as to this point. And, indeed, the purpose of 

 the direct tract is not clear ; there is no adequate evidence for the view which 

 has been held that these direct fibres are destined for the upper limbs and 

 upper part of the body ; since they are the last to cross we should, a priori, 

 be inclined to suppose that they were distributed to lower rather than higher 

 parts. 



578. We may now briefly summarize what we know concerning volun- 

 tary movements. And it will be convenient to trace the events in order 

 backward. 



Certain muscles are thrown into a contraction which even in the briefest 

 movements is probably of the nature of a tetanus. In almost every move- 

 ment more than one muscle, as defined by the anatomists, is engaged, and in 

 many movements a part of several muscles is employed, and not the whole 

 of each. It is perhaps partly owing to the latter fact that a muscle which 

 has become tired in one kind of movement, may show little or no fatigue 

 when employed for another movement, though we must bear in mind that in 

 a voluntary movement fatigue is much more of nervous than of muscular 

 origin. 



Besides the active muscles, if we may so call them, which directly carry 

 out the movement, the metabolism of which supplies the energy given out as 

 work done, other muscles, some of which are antagonistic to the active mus- 

 cles and some of which may be spoken of as adjuvant, enter into the whole 

 act. In flexion, for instance, of the forearm on the arm it is not the flexor 

 muscles only but the extensors also which are engaged. According to the 

 immediately preceding position and use of the arm, and according to the 

 kind and amount of flexion which is to be carried out, the extensors will be 

 either relaxed, that is to say, inhibited, or thrown into a certain amount of 

 contraction. And in some of the more complicated voluntary movements 

 the part played by adjuvant muscles is considerable. Hence, in a voluntary 

 movement the will has to gain access not only to the active muscles, but also 



