MOTOR CONDUCTION IN THE SPINAL COED. 281 



transmission is not effected exclusively by the white sub- 

 stance, but that the gray matter plays an important part in 

 this function. 1 "We shall refer, farther on, to the action of the 

 gray substance in the transmission of sensory impressions. 



It is evident, from anatomical facts as well as from the 

 results of direct experimentation, that the fibres of conduc- 

 tion of motor stimulus pass from the brain to the anterior 

 roots of the nerves, through the spinal cord, from above 

 downward, and that there is no other medium for the trans- 

 mission of the will to the muscles. Wherever the cord 

 be divided, all the muscles supplied by nerves given off be- 

 low the section are paralyzed. From the brachial enlarge- 

 ment of the cord, nerves of motion pass to the superior ex- 

 tremities, and the inferior extremities are supplied mainly 

 by nerves coming from the lumbar enlargement. The di- 

 rection of these motor fibres in the cord itself has only 

 been elucidated by experiments upon living animals. If the 

 anterior columns alone be divided in the dorsal region, there 

 is almost complete paralysis of the lower extremities. If the 

 lateral columns be divided in this situation, without injuring 

 the anterior columns, voluntary movements of the lower ex- 

 tremities are diminished, but are not abolished. If the an- 

 terior columns be divided high up in the cervical region, 

 there is a diminution in the voluntary movements, but by 

 no means so marked as when the section is made in the dor- 

 sal region ; but if the lateral columns be divided in the upper 

 cervical region, the paralysis is almost or quite complete. 2 



The experiments just cited clearly show that the situa- 

 tion of the chief motor conductors of the cord is different in 

 the dorsal and in the cervical region. In the dorsal region, 

 while conduction of the motor stimulus takes place through 

 fibres contained both in the anterior and in the lateral 



1 YULPIAN, Lemons sur la physiologie generate et comparee du systeme nerveux, 

 Paris, 1866, p. 369. 



2 BROWX-SEQUARD, Physiology and Pathology of the Central Nervous System, 

 Philadelphia, 1860, p. 46. VULPIAN, Systeme nerveux, Paris, 1866, p. 370. 



