THE CENTRAL NEKVOUS SYSTEM 387 



On this same side cut all the posterior roots. 



No stimulus applied to the right leg will now 

 discharge a reflex action. But stimuli applied to 

 sensory nerves elsewhere may still cause reflex 

 movements of the right leg. Motor impulses still 

 pass to these muscles. But only the anterior 

 roots remain. 



Hence the anterior roots of spinal nerves trans- 

 mit motor impulses from the spinal cord towards 

 the muscles (efferent impulses) ; the posterior 

 roots transmit sensory impulses from sensory sur- 

 faces towards the spinal cord (afferent impulses.) 



Ludwig's Demonstration. Destroy the brain 

 of a large frog with the seeker. Remove the 

 thoracic and abdominal viscera, taking care not 

 to injure the sciatic nerve plexus. Remove the 

 7th and 8th vertebrae, taking the greatest pains 

 not to injure the nerve roots. Divide the body 

 transversely at this level, so that the anterior 

 and posterior halves shall remain connected only 

 by the anterior and posterior sciatic roots. Keep 

 the roots moist with normal saline solution. 



Demonstrate again that the anterior roots 

 transmit efferent, and the posterior roots afferent 

 impulses. 



Localization of Movements at Different Levels of 

 the, Spinal Cord. Separate the three roots which 

 form the sciatic nerve. After tying a thread 



