230 CEREBRAL LOCALIZATION 



left cortex in right-handed people, and that the 

 precentral convolutions are merely the departure 

 platforms for messages from the brain to the cord. 

 Instructions are sent to the right precentral convolu- 

 tion by way of the corpus callosum. It is still in 

 doubt whether the above-mentioned initiating centre 

 is i7i the left precentral gyrus, or whether it lies iyi 

 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 much interest. 

 Recent studies of the subject have been very revolu- 

 tionary in their tendency. We used to learn that 

 there were three main centres for the appreciation 

 and utterance of language, namely : — 



