290 NERVOUS SYSTEM. 



"I have long been impressed with the opinion, that the 

 office of the posterior columns of the spinal cord is very dif- 

 ferent from any yet assigned to them. Theyjnay be in part 

 commissural between the several segments of the cord, serv- 

 ing to unite them and harmonize them in their various ac- 

 tions, and in part subservient to the function of the cerebel- 

 lum in regulating and coordinating the movements necessary 

 for perfect locomotion." l Todd further states, that this view 

 is supported by the phenomena observed in cases of disease 

 " distinguished by a diminution or total loss of the power of 

 coordinating movements. ... In two examples of this va- 

 riety of paralysis, I ventured to predict disease of the poste- 

 rior columns, the diagnosis being founded upon the view^s 

 of their functions which I now advocate ; and this was found 

 to exist on post-mortem inspection ; and in looking through 

 the accounts of recorded cases in which the posterior col- 

 umns were the seat of lesion, all seem to have commenced 

 by evincing more or less disturbance of the locomotive pow- 

 ers, sensation being affected only when the morbid change 

 of structure extended to and more or less involved the pos- 

 terior roots of the spinal nerves." 3 



It is only necessary to add that the views of Todd have 

 been in the main confirmed in the numerous cases of loco- 

 motor ataxia that have lately been so fully described by 

 pathologists ; and, from these facts, it is more than probable 

 that the posterior columns contain fibres connecting the dif- 

 ferent segments of the cord, and that they play an important 

 part in the coordination of muscular movements. The gen- 

 eral function of coordination will be again considered in con- 

 nection with the cerebellum. 



Decussation of the Sensory Conductors of the Cord. In 

 hemiplegia due to injury of the brain, the paralysis occurs 



1 TODD, Cyclopcedia of Anatomy and Physiology, London, 1839-1847, vol. Hi., 

 p. 721, Q, Article, Nervous System. 

 9 Op. *., p. 721, R. 



