75 2 A MANUAL OF PHYSIOLOGY 



meaning, or utters a jargon not composed of known words at all. 

 The failure does not lie in the articulatory mechanism. The patient 

 uses the same muscles of articulation, without any marked impair- 

 ment of function, for chewing and swallowing his food. It is only 

 when the corresponding area in the right inferior frontal convolution, or 

 the path from it to the internal capsule, is also destroyed, that articu- 

 lation is greatly and permanently interfered with. An aphasic may 

 sometimes sing a song without a single slip in words or measure, 

 and yet be unable to speak or write it. In a case recorded by 

 Larionow an aphasic could speak only one syllable, * tan,' but could 

 sing the Marseillaise. In certain cases the change is confined to 

 loss of the power of spontaneous speech, and the patient may be 

 able to read intelligently. Sometimes he can express his ideas in 

 speech but not in writing (agraphia). Sometimes the loss is 

 restricted to certain sets of ideas. For example, a boy was injured 

 by falling on his head. Typical symptoms of motor aphasia deve- 

 loped, but the power of dealing with ideas of number was not inter- 

 fered with, and the boy continued to learn arithmetic as if nothing 

 had happened. Proper names and nouns are more easily lost than 

 adjectives and verbs. Motor aphasia is generally accompanied by 

 paralysis, frequently transient, of voluntary movement on the right 

 side, sometimes amounting to complete hemiplegia, but more often 

 involving the right arm alone. This association is explained by the 

 proximity of the inferior frontal convolution to the motor area of the 

 arm, and their common blood-supply. 



Why, now, is it that motor aphasia is commonly due to a lesion 

 in the left hemisphere alone ? The answer to this question is partly 

 supplied by the important and curious observation that in left- 

 handed individuals damage to the right inferior frontal convolution 

 may cause aphasia. In the right-handed man the motor areas of the 

 left hemisphere may be supposed to be more highly educated than 

 those of the right hemisphere. The movements of the right side 

 which they initiate or control are stronger and more delicate and 

 precise than those of the left side. It is only necessary to assume 

 that this process of specialization, of selective training, has been 

 carried on to a still greater extent in the left frontal convolution, 

 that in most men the speech-centre there has taken upon itself the 

 whole, or the greater part, of the labour of clothing ideas in words, 

 leaving to the right centre only its primitive but undeveloped powers. 

 In left-handed persons the speech-centre on the right side may be 

 supposed to share in the general functional development of the right 

 hemisphere. That great capabilities are lying dormant in the right 

 speech-centre of the ordinary right-handed individual is indicated by 

 the fact that after complete destruction of the left inferior frontal 

 convolution the power of speech may be to a considerable extent, 

 though slowly and laboriously, regained ; and it is said that this 

 second accumulation may be swept away, and without remedy, by 

 a second lesion in the right inferior frontal convolution. But frail is 

 the tenure of life in a person who has twice suffered from such a 

 lesion ; and we do not know whether recovery might not take place 



