THE NERVOUS SYSTEM. 629 



does not, however, appear the rule when the brain of a dog is used 

 instead of that of the monkey. It is suggested that in the animal lower 

 in the scale, the functions which in the monkey are discharged by the 

 cortical centres may be subserved by the basal ganglia. 



Motorial Areas of the Human Brain. It is naturally of great impor- 

 tance to discover how far the result of experiments upon the dog and 

 monkey hold good with regard to the human brain. Evidence furnished 

 by diseased conditions is not wanting to support the general idea of the 

 existence of cortical motorial centres in the human brain (fig. 382). 



Fig. 382. The Cortical Centres. (Dana.) 



So far, however, it has been possible to localize motor functions in 

 the frontal and ascending parietal convolutions only, to the convolutions 

 which bound the fissure of Rolando, and to those on the inner side of 

 the hemispheres which correspond thereto, and possibly to the frontal 

 lobe in front of the ascending convolution. 



The position of the centres is probably much the same as in the mon- 

 key's brain those for the leg above, those for the arm, face, lips, and 

 tongue from above downward. Destruction of these parts causes pa- 

 ralysis, corresponding to the district affected, and irritation causes con- 

 vulsions of the muscles of the same part. Again, a number of cases 

 .are on record in which aphasia, or the loss of power of expressing ideas 

 in words, has been associated with disease of the posterior part of the 

 lower or third frontal convolution on the left side. This condition is 

 usually associated with paralysis of the right side (right hemiplegia). 



This district of the brain is now generally known as the motor area; 

 and there seems no doubt whatever that from this area pass the nerve- 



