310 



THE NERVOUS SYSTEM 



of the opposite hemisphere, since no relapse occurs when 

 the opposite side is subsequently ablated. Motor control 

 appears to be taken over by the lower centres. 



Irritative lesions of the motor area cause a peculiar kind 

 of fit, known as Jacksonian epilepsy. The movement of 



Toes 

 Ank/e^\ 

 Knee 



Anus & Vagina 



.■ Sulcus , . 

 . centra I IS 



Abdomen 

 ,Chest 



Shoulder 

 Elbow 

 Wrist^' 



Finders 

 & thumb 



Ear--" .^ . 



Eyelid, -'Closure , 



Nose °^ j^^ Opening \ 



of jaw \/ocal 



cords MasticdTiop 



Sulcus centralis 



Fig. 55. — Outer surface of brain of chimpanzee, showing movements 

 obtained by electrical stimulation (Sherrington). 



the limbs is at first tonic, then clonic or rhythmic. The 

 disturbance spreads from a focus to adjacent areas in the 

 order of their proximity (the march of the fit), and in 

 severe cases involves the whole side of the body and even 

 the opposite side. Unhke ordinary epilepsy, the cause of 

 which is unknown, Jacksonian epilepsy is usually not 

 accompanied by loss of consciousness. 



