NERVE 191 



The evidence as regards its position is both clinical and 

 experimental. 



1. Clinical and Pathological Evidence. — Destructive lesions 

 of this area on one side cause a loss of the so-called 

 voluntary action of groups of muscles on the opposite side of 

 the body, while the muscles themselves and the spinal reflexes 

 connected with them are not interfered with. The spinal 

 reflexes may in fact become more active. 



Certain lesions may directly stimulate these centres, 

 causing them to act without the previous action of the 

 other cerebral mechanisms and may cause convulsions. 

 This is seen in Jacksonian epilepsy, where, as the result 

 of a spicule of bone or a thickened bit of membrane, one 

 part of the cortex is from time to time excited. This pro- 

 duces movements of certain groups of muscles, which spread 

 outwards to other groups as the stimulation of the cortex 

 extends outwards from its seat of origin, till finally all the 

 muscles of the body are involved in a general convulsion 



2. Experimental Evidence. — Experimental observations 

 have fully confirmed and extended the conclusions arrived at 

 from such pathological evidence. 



(a) Removal. — If parts of these convolutions be excised 

 in the monkey, the animal loses the power of voluntary 

 movement of certain groups of muscles on the opposite side 

 of the body. Movements requiring the co-operative action 

 of muscles of both sides, e.g. movements of the eyes and 

 trunk, are not abolished by unilateral destruction. 



In these motor areas the lesion must be extensive to 

 cause complete iJaralysis of any group of muscles. A limited 

 lesion may simply cause a loss of the finer movements. 

 Thus, a monkey with part of the middle portion of the 

 Rolandic areas removed mav be able to move its arm and 

 hand, but may be quite unable to pick up objects from the 

 floor of its cage. 



Even after removal of a fairly extensive part of these 

 centres, with resulting muscular paralysis, it has been found 

 that after a time more or less complete recovery takes place. 

 Evidently some other part than that removed can take upon 



