662 Dynamic TJieory. 



This patch of brain appears to possess functions of combination in re- 

 gard to the motor actions concerned in speech, much like those of the 

 cerebellum in relation to the muscular co-ordinations concerned in the 

 common motions of walking, balancing, &c. When Aphasia or loss of 

 speech is due to the failure of these centers, the subject loses the faculty 

 of articulation and generally the power of writing his thoughts, although 

 he can still understand the meaning of spoken and perhaps written 

 words. That the disease is due to a loss of the combining power of 

 nervous stimulations and not to the paralysis of the muscles concerned, 

 is proved by the fact that the same muscles are still employed in chew- 

 ing, swallowing, &c. The cause of the disease is generally due to em- 

 bolism, or a plugging up of some of the blood vessels supplying this 

 part of the brain. This deprives the part of nourishment and finalty 

 causes its softening and destroys its function. The same stoppage is 

 liable to affect other brain centers supplied by the same arterial trunks 

 ( of the middle cerebral artery ), and so ma} r cause the destruction ( in 

 right-handed persons ) of the motor centers governing movements of the 

 right hand and face, so that paralysis of those parts is apt to accompany 

 aphasia. After speech has been lost by lesion of the left motor speech 

 center, there are cases on record in which it has been reacquired b} T the 

 education of the corresponding center on the right side. There is reason 

 to doubt whether the education of the right speech center is entirely 

 avoided as often as the physiologists appear to think. There are many 

 cases of aphasia accompanied by left hemiplegia showing that in such 

 cases the motor speech center was on the right side and became involved 

 with the centers for muscular motion on that side. It seems probable 

 that in many cases both sides are educated, one perhaps more than the 

 other. 



There is another form of aphasia called Amnesia (forgetfulness), or 

 sensory aphasia. This arises from lesions of the centers of sight or of 

 hearing. When a certain sight center is impaired, particularly the an- 

 gular gyrus of the left hemisphere, (see 13, fig. 359 ; A G, fig. 360 ; 

 13, 13', fig. 362) the person loses the memory of the associated writ- 

 ten symbol, which belongs to a particular articulate sound ; that is, hav- 

 ing the written symbol he cannot translate it into spoken language or 

 tell what it means, although he can understand spoken language, and 

 even write from dictation. In the case of failure of the hearing center, 

 the person cannot understand spoken language or repeat what he hears, 

 while still able to articulate what he sees written. The auditory center 

 is the " superior tempero-sphenoidal convolution. " (14, fig. 362.) What 

 is lost in sensory aphasia is not general vision or hearing, but the asso- 

 ciation between these senses and articulate sounds and written symbols, 

 respectively. So it does not necessarily follow in all cases of amnesia, 



