40 PSYCIIOLOOY. 



ever, it would a])pear (from the facts of aphasia) that the 

 left hemisphere in most ])ersous liabitually takes exclusive 

 -charge. With that hemisphere thrown out of gear, speech is 

 undone ; even though the ojiposite hemisphere still be there 

 for the performance of less specialized acts, such as the 

 "various movements required in eating. 



It will be noticed that Broca's region is homologous 

 with the parts ascertained to produce movements of the 

 lips, tongiie, and larynx when excited by electric currents 

 in apes (cf. Fig. 6, p. 34). The evidence is therefore as com- 

 plete as it well can be that the motor incitations to these 

 organs leave the brain by the lower frontal region. 



Victims of motor aphasia generally have other disorders. 

 One which interests us in this connection has been called 

 agraphia : they have lost the power to ivrite. They can 

 read writing and understand it ; but either cannot use the 

 pen at all or make egregious mistakes with it. The seat 

 of the lesion here is less well determined, owing to an in- 

 sufficient number of good cases to conclude from.* There 

 is no doubt, however, that it is (in right-handed people) on 

 the left side, and little doubt that it consists of elements 

 of the hand-and-arm region sjjecialized for that service. 

 The symptom may exist when there is little or no disability 

 in the hand for other uses. If it does not get well, the 

 ' patient usually educates his right hemisphere, i.e. learns 

 to write with his left hand. In other cases of which we 

 shall say more a few pages later on, the patient can write 

 both spontaneously and at dictation, but cannot read even 

 what he has himself Avritten ! All these phenomena are 

 now quite clearly explained by separate brain-centres for 

 the various feelings and movements and tracts for associat- 

 ing these together. But their minute discussion belongs to 

 medicine rather than to general psychology, and I can only 

 use them here to illustrate the principles of motor locali- 

 zation.f Under the heads of sight and hearing I shall 

 have a little more to say. 



* Nothnagel und Nauuyn : Die Localization in den Gehirnkrankheiten 

 (Wiesbaden,l887), p. 34. 



f An accessible account of the history of our knowledge of motor 

 aphasia is in W. A. Hammond's 'Treatise on the Diseases of the Nervous 

 System,' chapter vii. 



