October 25, 1901.] 



SCIENCE, 



643 



est attached to the subject is very consider- 

 able, 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 shap- 

 ing 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. 



N^ot one of these theories when closely 

 looked into is found to possess the smallest 

 degree of value. Braune* has shown in 

 the most conclusive manner that if there is 

 any difference in weight between the two 

 hemispheres it is a difference in favor 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 de- 

 velopment. 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 I can corroborate Eckerf in his 

 statement that there is no proof that the 



* ' Das Gewichtsverhaltniss der rechten zur linken 

 Hirnhalfte beim Menschen,' Archiv fur Anat. 

 f Archiv fur Anthropologie, 1868, Bd. CXI. 



convolutions appear earlier on the one side 

 than on the other. The theory that an ex- 

 planation is to be found in a more generous 

 blood supply to the left hemisphere is more 

 difficult to combat, because the amount of 

 blood received by each side of the brain de- 

 pends upon two factors, viz., the physical 

 conditions under which the blood-stream is 

 delivered to the two hemispheres and the 

 caliber of the arteries or tubes of supply. 

 Both of these conditions have been stated 

 to be favorable to the left hemisphere. It 

 is a matter of common anatomical knowl- 

 edge that the supply pipes to the two sides 

 of the brain are laid down somewhat differ- 

 ently, and that the angles of junction, etc., 

 with the main pipe are not quite the same. 

 Further, it is true that the blood-drains 

 which lead away the blood from the brain 

 are somewhat different on the two sides. 

 Whether this would entail any marked dif- 

 ference in the blood-pressure on the two 

 sides I am not prepared to say. This 

 could only be proved experimentally ; but, 

 taking all the conditions into consideration, 

 I am not inclined to attach much impor- 

 tance to the argument. It is easy to deal 

 with the loose statements which have been 

 made in regard to the size of leading supply 

 pipe (viz., the internal carotid artery). It 

 passes through a bony canal on the floor of 

 the cranium on its way into the interior of 

 the cranial box. Its size can therefore be 

 accurately gauged by measuring the sec- 

 tional area of this bony tunnel on each side. 

 This I have done in twenty-three skulls 

 chosen at random, and the result shows 

 that considerable differences in this respect 

 are to be found in different skulls. These 

 discrepancies, however, are sometimes in 

 favor of the one side and at other times in 

 favor of the other side, and when the com- 

 bined sectional area for all the skulls ex- 

 amined was calculated, it was, curiously 

 enough, found to be 583|^ sq. mm. for the 

 left side and 583 sq. mm. for the right side. 



