1102 CUTANEOUS SENSATIONS. [BOOK m. 



Clinical histories moreover agree, at least to large extent, in 

 shewing that when the lesion is confined to one half of the cord, 

 the sensations affected in the parts below the level of the lesion are 

 chiefly or even exclusively those of the crossed side. But there is 

 not entire accordance, especially as to the crossing being complete. 

 And with regard to the muscular sense there is a distinct conflict 

 of opinion ; the majority of cases seem to shew that in unilateral 

 disease or injury to the cord, the muscular sense in company with 

 the voluntary movements, fails on the same side ; but cases have 

 been recorded in which the muscular sense in company with other 

 sensations, seemed to be affected on the crossed side ; it must be 

 remembered however that it is very difficult to appreciate a 

 deficiency of muscular sense mingled with deficiencies in other 

 sensations, and we should a priori expect the muscular sense to 

 run parallel with motor impulses. 



When however we appeal to clinical histories or indications as 

 to the several paths within the spinal cord taken by these several 

 impulses, the answer is a most uncertain one, as indeed might be 

 expected from the too often diffuse character of the lesions of 

 disease ; and it is perhaps not too much to say that no satisfactory 

 deductions at all can be made. 



684. Whether then we turn to experiments on animals or 

 to the study of disease, the teachings with regard to sensation, in 

 contrast to those with regard to voluntary movement, are in the 

 highest degree uncertain and obscure. A few general reflections 

 will perhaps help us to appreciate the value of such facts as we 

 possess. 



We have seen reason to think that in every movement whether 

 voluntary and of cortical origin, or involuntary and started either 

 as a simple spinal reflex or through the working of some part 

 or other of the brain, the motor impulses, which sweep down the 

 motor fibres to the muscles, issue marshalled and coordinated from 

 the grey matter of the cord (for the sake of clearness we may omit 

 the cranial nerves), from what we have called the motor mechan- 

 isms of the cord. Analogy would lead us to suppose that the 

 afferent impulses, forming the bases of the several kinds of sensa- 

 tions, similarly left the afferent fibres to join the grey matter of 

 the cord in what we may call the sensory mechanism. And such 

 anatomical leading as we possess seems to support this view ; with 

 the exception of the median posterior tract, to which we will return 

 immediately, all the fibres of a posterior root seem to end in the 

 grey matter not very far from the entrance of the root. We have 

 seen that a coordinate reflex movement may be carried out by at 

 least a few segments of the cord ; that a reflex movement may 

 be started by stimuli of various kinds and therefore presumably 

 by afferent impulses of various kinds ; and that impulses forming 

 the basis of the muscular sense are essential to the coordination of 

 the movement. All our knowledge goes to shew that in a reflex 



