498 THE NERVOUS SYSTEM. 



Sequard have cast much, new light on all relating to 

 the functions of the spinal cord. It is not possible to 

 do justice to these investigations in any summary, how- 

 ever lengthy and complete: the whole series (delivered 

 in lectures at the College of Surgeons) must be 

 read and studied. An attempt will be made here to 

 point out only the principal conclusions deducible from 

 them. 



a. Sensitive impressions, conveyed to the spinal cord by 

 root-fibres of the posterior nerves are not conducted to the 

 brain by the posterior columns of the cord, as hitherto has 

 been generally supposed, but pass through them into the 

 central grey substance, by which they are transmitted to 

 the brain (fig. 142). 



b. The impressions thus conveyed to the grey substance 

 do not pass up to the brain along that half of the cord 

 corresponding to the side from which they have been 

 received, but, almost immediately after entering the cord, 

 cross over to the other side, and along it are transmitted 

 to the brain. There is thus, in the cord itself, a complete 

 decussation of sensitive impressions brought to it ; so that 

 division or disease of one posterior half of the cord is 

 followed by lost sensation, not in parts on the correspond- 

 ing, but in those of the opposite side of the body. 



c. The various sensations of touch, pain, temperature, 

 and muscular contraction, are probably conducted along 

 separate and distinct sets of fibres. All, however, with 

 the exception of the last named, undergo decussation in the 

 spinal cord, and along it are transmitted to the brain by 

 the grey matter. 



d. The posterior columns of the cord appear to have a 

 great share in reflex movements, and this is the principal 

 cause of the peculiar kind of paralysis so often observed in 

 disease of these columns. 



e. Impulses of the will, leading to voluntary contractions 

 of muscles, appear to be transmitted principally along the 



