DECUSSATTOF OF, THE SENSORY CONDUCTOKS. 291 



upon the side of the body opposite to the cerebral lesion. 

 The phenomena ordinarily observed are simply paralysis of 

 motion ; but in those cases in which both motion and sensa- 

 tion are abolished upon one side of the body, the lesion in 

 the brain is found to be upon the opposite side. It is evi- 

 dent, therefore, that there is a decussation of the conductors 

 of sensory impressions as well as of the conductors of the mo- 

 tor stimulus. 



As early as 1822, Fodera made a longitudinal section of 

 the spinal cord in the lumbar region, exactly in the median 

 line. In this experiment, " sensation was destroyed, and in 

 part motion upon the two sides." * Inasmuch as in this sec- 

 tion it is only possible to divide the fibres, passing from one 

 lateral half of the cord to the other, it is evident that the 

 sensory conductors must decussate in the spinal cord itself. 

 As far as we know, this is the first experiment pointing to 

 the decussation of sensory fibres in the cord, the observations 

 of Galen, to which we have already referred, being limited 

 to the phenomena of motion. 3 



The next experiments bearing upon the decussation of 

 the sensory conductors in the cord are those of Yan Deen. 

 Among the numerous observations made upon the spinal 

 cord by this physiologist, are one or two in which he noted 

 the fact that, after section of one lateral half of the cord in 

 the frog, at the site to the third dorsal vertebra, " the animal 

 had no real loss of sensibility in the posterior extremity on 

 the side on which the half of the spinal cord had been cut." 3 

 Although Yan Deen did not distinctly state, as a conclusion 

 drawn from these observations, that there is decussation of 

 the sensory conductors in the cord, the fact of section of one 

 lateral half of the cord with no loss of sensation on the cor- 



1 FODERA, Recherches experimentales sur le systeme nerveux, presentees d 

 T Academic des sciences, le 31 decembre, 1822. Journal de phy&dogie, Paris, 1823, 

 tome ill, p. 199. 



9 See page 284. 



3 VAN BEEN, Traiies et decouvertes sur la physiologic de la moette epinere, 

 Leide, 1841, pp. 65, 92. 



