CROSSED ACTION OF THE SPINAL CORD. 405 



If the anterior columns of the spinal cord, therefore, be wounded 

 at any point in the cervical, dorsal, or lumbar region, a paralysis 

 of voluntary motion is produced in the limbs below, on the same 

 side with the injury. But if a similar lesion occur in the brain, the 

 paralysis which results is on the opposite side of the body. Thus 

 it has long been known that an abscess or an apoplectic hemorrhage 

 on the right side of the brain will produce paralysis of the left side 

 of the body; and injury of the left side of the brain will be fol- 

 lowed by paralysis of the right side of the body. 



The spinal cord has also a crossed action in transmitting sensi- 

 tive as well as motor impulses. It has been recently demonstrated 

 by Dr. Brown-Se'quard, 1 that the crossing of the sensitive fibres in 

 the spinal cord does not take place, like that of the motor fibres, 

 at its upper portion only, but throughout its entire length ; so that 

 the sensitive fibres of the right spinal nerves, very soon after their 

 entrance into the cord, pass over to the left side, and those of the 

 left spinal nerves pass over to the right side. For if one lateral 

 half of the spinal cord of a dog be divided in the dorsal region, 

 the power of sensation remains upon the corresponding side of the 

 body, but is lost upon the opposite side. It has been shown, fur- 

 thermore, by the same observer, 2 that the sensitive fibres of the 

 spinal nerves when they first enter the cord join the posterior 

 columns, which are everywhere extremely sensitive ; but that they 

 very soon leave the posterior columns, and, passing through the 

 central parts of the cord, run upward to the opposite side of the 

 brain. If the posterior columns, accordingly, be alone divided at 

 any part of the spinal cord, sensibility is not destroyed in all the 

 nerves behind the seat of injury, but only in those which enter the 

 cord at the point of section ; since the posterior columns consist 

 of different nervous filaments, joining them constantly on one side 

 from below, and leaving them on the other to pass upward toward 

 the brain. 



The spinal cord has therefore a crossed action, both for sensation 

 and motion ; but the crossing of the motor filaments occurs only at 

 the medulla oblongata, while that of the sensitive filaments takes 

 place throughout the entire length of the cord. 



1 Experimental Researches applied to Physiology and Pathology. New York. 

 1853. 



2 Memoirs sur la Physiologic de la Moelle epiniere ; Gazette Medicale de Paris, 

 1855. 



