166 CEREBRAL LOCALIZATION 



is in the left precentral gyms, or whether it lies in 

 front of this, in the first and second frontal convolu- 

 tions, as most neurologists maintain. It is quite 

 certain that a lesion of the front part of the corpus 

 callosum is characterized by apraxia of the left arm ; 

 this important discovery may well lead to successful 

 surgical removal of tumours there situated. A lesion 

 in the left frontal cortex may cause apraxia of both 

 arms ; there will probably be right hemiplegia as 

 well, which would mask the condition in the right arm. 

 To sum up, a lesion is cortical if there are present : 



1. A monoplegia. 



2. Hemiplegia with either (i) Aphasia which 

 persists ; (ii) Recurring convulsions ; (iii) Flac- 

 cidity ; (iv) Apraxia of the opposite side. 



Left-sided apraxia without hemiplegia indicates a 

 lesion of the corpus callosum. 



APHASIA. 



The various types of aphasia have always presented 

 problems of great complexity but of great interest. 

 Recent studies of the subject have been very revolu- 

 tionary in their tendency. We used to learn that 

 there were three great centres for the appreciation 

 and utterance of language, namely : 



1. The motor centre, controlling utterance, in 

 Broca's convolution (the third left frontal). 



2. The auditory word centre, appreciating spoken 

 language, in the posterior part of the second left 

 temporal convolution. This was also regarded as 

 dominating and being necessary for the activity of 

 the other two centres. 



