THE NERVOUS SYSTEM 



499 



The effect of removing the motor areas differs according to 

 the animal. In the monkey it results in permanent motor paralysis 

 of hand or foot, but not of parts with less skilled movements — 

 e.g., shoulder or knee. In the sheep, as we have just seen, 

 there is no paralysis. In the dog paralysis is not necessarily 

 produced, and it has been supposed that the basal ganglia are 

 capable in this animal of taking on the duties of the cortex. 

 The destruction which has been observed at times in the cortex 

 of the horse is commonly unaccompanied by any symptoms 

 until shortly before death. Colin draws attention to the dim- 



Face, mouth, and 

 tongue 



Head and eyes 

 Fore-limb 

 Hind-limb 



Tig. 152. 



-Diagram showing Position of Motor Areas on Dorsal Aspect 

 Brain of Sheep (Simpson and King). 



culty in producing paralysis experimentally in the horse from 

 lesions of the hemispheres. Neither the artificial production of 

 a clot in the falciform sinus, nor the introduction of pieces of 

 lead the size of a pea into the convolutions, gave rise to hemi- 

 plegia. This quite bears out a frequently observed clinical fact, 

 that it is possible for horses to have tumours the size of an egg 

 in their lateral ventricles without producing any disturbance. 

 The writer has seen several such cases, the tumours being of 

 variable size, and the clinical history has never given more 

 than a few days' illness, though the growths must have 

 been forming for a considerable period. 



Strong stimulation of the motor areas produces epilepsy. By 



