SUMMARY -OF THE SPINAL COED. 295 



cord in two places, so as to have three pairs of nerves be- 

 tween the two sections, we find that the middle pair has 

 almost the same degree of sensibility as if nothing had been 

 done to the spinal cord, while the two other pairs have a 

 diminished sensibility, the upper one particularly in its upper 

 roots, and the lower one in its lower roots ; which facts seein 

 to show that the ascending fibres of the upper pair, and the 

 descending fibres of the lower one, have been divided before 

 they had made their decussation. 



If there is only one pair of nerves between two sections, 

 its sensibility is almost entirely lost, as then the transversal 

 fibres are almost alone uninjured (most of the ascending and 

 descending being divided), which fibres are employed for 

 reflex action, and hardly for the transmission of sensitive 

 impressions." l 



The experimental facts just cited conclusively show de- 

 cussation of sensory conductors in the cord in the animals 

 operated upon, and this has been sufficiently confirmed by 

 other experimenters to render the fact certain. It is possi- 

 ble that the decussation may not be so complete in some 

 other classes of animals, which would account for the results 

 obtained by those who have denied decussation ; but cases 

 of disease of the cord in the human subject all go to show 

 that the crossed action is complete in man. 



/Summary of the Action of the Spinal Cord as a Conductor. 



The antero-lateral columns of the cord, comprising that 

 portion included between the anterior median fissure and the 

 origin of the posterior roots of the nerves, are insensible to 

 direct irritation, and serve as conductors of the motor stimu- 

 lus from the brain to the anterior roots of the nerves. If 

 these columns be divided, voluntary motion is lost in all 

 parts below the section. If the rest of the cord be divided, 

 leaving the antero-lateral columns intact, the power of volun- 



1 BROWX-SEQUARD, Central Nervous System, Philadelphia, 1860, p. 36. 



