784 REPORT— 1901. 



Now, it requires a very slight acquaintance with the cerebral surface to perceive 

 that the great and leading peculiarity of the human brain ii5 the wide extent of 

 these higher association centres of Flechsig. Except in connection with new 

 faculties, such as speech, there has been relatively no striljing increase in the extent 

 of the motor areas in man as compared with the cortex of the ape or the idiot, but 

 the expansion of the association areas is enormous and the increase in the frontal 

 region and the back part of the parietal region is particularly well marked. It is 

 this parietal extension of surface which is chiefly responsible for the pushing down 

 of the lower frontier of the parietal lobe and the consequent enlargement of its 

 territory. 



I have already referred to the views which have been recently urged by several 

 independent observers, that in the men who have been distinguished during life 

 by the possession of exceptional intellectual power, this region has shown a A'ery 

 special development. 



It is a curious circumstance, and one which is worthy of consideration, that in 

 the left cerebral hemisphere the Sylvian fissure or the lower boundary of the 

 parietal lobe is more depressed than in the right hemisphere, and, as a result of 

 this, the surface area occupied by the parietal lobe is greater on the left side of the 

 brain than on the right side. To the physiologist it is a matter of every-day 

 knowledge that the left cerebral hemisphere shows in certain directions a marked 

 functional pre-eminence. Through it the movements of the right arm and right 

 side of the body are controlled and regulated. Within it is situated also the active 

 speech centre. This does not imply that there is no speech centre on the right 

 side, but simply that the left cerebral hemisphere has usurped the chief, if not the 

 entire, control of this all-important function, and that from it are sent out the chief 

 part, if not the whole, of the motor incitations which give rise to speecli. The 

 significance attached to the dominant power of the left hemisphere receives force 

 from the now well established fact that iu left-handed individuals the speech func- 

 tion is also transferred over to the right side of the brain. To account for this 

 functional pre-eminence of the left cerebral hemisphere numerous theories have 

 been elaborated. The interest attached to the subject is veiy considerable, but it 

 is impossible on the present occasion to do more than indicate in the briefest 

 manner the three views which have apparently had the widest influence in shaping 

 opinion on this question. They are: (1) that the superiority of the left cerebral 

 hemisphere is due to its greater weight and bulk ; (2) that it may be accounted for 

 by the greater complexity of the convolutions on the left brain and the fact that 

 these make their appearance earlier on the left side than on the right side ; (3) that 

 the explanation lies in the fact that the left side of the brain enjoys greater 

 advantages in regard to its blood supply than the right side. 



Not one of these theories when closely looked into is foimd to possess the 

 smallest degree of value. Braune ^ has shown in the most conclusive manner that 

 if there is any difli"erence in weight between the two hemispheres it is a difiference 

 in favour of the right and not of the left hemisphere ; and I may add from my own 

 observations that this is evident at all periods of growth and development. 

 Equally untrustworthy are the views that have been put forward as to the superiority 

 of the left hemisphere from the point of view of convolutionary development. I 

 am aware that it is stated that in two or three cases where the brains of left- 

 handed people have been examined this superiority was evident on the right 

 hemisphere. This may have been so ; I can only speak for the large percentage 

 of those who are right-handed ; and I have never been able to satisfy myself that 

 either in the growing or fully developed brain is there any constant or marked 

 superiority in this respect of the one side over the other ; and 1 can corroborate 

 Ecker ~ in his statement that there is no proof that the convolutions appear earlier 

 on the one side than the other. The theory that an explanation is to be found iu 

 a more generous blood supply to the left hemisphere is more difficult to combat, 



' ' Das Gewichtsverhiiltniss der rechten zur linken Hiruhtllfte beim Menschen,' 

 Archiv fiir An at. 



■ Arcliivfar Anthrojyologie, 1868, Bd. cxi. 



