CONDUCTION BY THE SPINAL CORD. 



499 



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 



Fig. I35-* 



central grey substance, by which alone, or aided by the 

 anterior columns, they are transmitted to the brain 



* The above diagram (after Brown- Sequard) represents the decussation 

 of the conductors for voluntary movements, and those for sensation : a, r, 

 anterior roots and their continuations in the spinal cord, and decussation 

 at the lower part of the medulla oblongata, mo\ pr, the posterior roots 

 and their continuation and decussation in the spinal cord; gg, the 

 ganglions of the roots. The arrows indicate the direction of the 

 nervous action; r, the right side; I, the left side, i, 2, 3, indicate 

 places of alteration in a lateral half of the spino-cerebral axis, to show 

 the influence on the two kinds of conductors, resulting from section of 

 the cord at any one of these three places. 



