FUNCTIONS OF THE BRAIN. 



39 



the lowest frontal gyrus (see Fig. 11) is the seat of injury. 

 Broca first noticed this fact in 1861, and since then the 

 gyrus has gone by the name of Broca' s convolution. The 



Fia. 11.— Schematic Profile of Left Hemisphere, with the parts shaded whose 

 destruction causes motor (' Broca ') and seusorj C" Wernicke ') Aphasia. 



injury in right-handed people is found on the left hemi- 

 sphere, and in left-handed people on the right hemisphere. 

 Most people, in fact, are left-brained, that is, all theif 

 delicate and specialized movements are handed over to 

 the charge of the left hemisphere. The ordinar}^ right- 

 handedness for such movements is only a consequence of 

 that fact, a consequence which shows outwardly on account 

 of that extensive decussation of the fibres whereby most of 

 those from the left hemisphere pass to the right half of the 

 body only. But the left-brainedness might exist in equal 

 measure and not show outwardly. This would happen 

 wherever organs on both sides of the body could be gov- 

 erned by the left hemisphere ; and just such a case seems 

 offered by the A^ocal organs, in that highly delicate and 

 special motor service which we call speech. Either hemi- 

 sphere can innervate them bilaterally, just as either seems 

 able to innervate bilaterally the muscles of the trunk, ribs, 

 and diaphragm. Of the special movements of speech, how- 



