1907.] on Dexterity and the Bend Sinister. 641 



side in these men and women, they onght to have grown up left-handed, 

 and the estabhshed fact that they were just as right-handed as ordinarily 

 constructed mortals is a conclusive proof that he was wrong. 



But Professor Cuunyngham of Edinburgh, accepting all this, still 

 thinks that there may be some truth in Buchanan's theory. Right- 

 handedness, he says, is a character not acquu-ed independently by each 

 individual and perishing with him without transmission to oifspring, 

 ])ut attained in the ordinary course of evolution, by natural selection. 

 A variation which tended to place this attribute of man on the more 

 favourable (that is to say the heavier side) is one which would be 

 strengthened and fostered until in the end it would become a 

 permanent possession of man — a possession which would not even be 

 disturbed by the transference of the bodily conditions which led to its 

 acquisition, to the other side of the body. That is tantamount to saying 

 that the greater weight of the right side of the body originally started 

 right-handedness but has nothing to do with its maintenance as its 

 immediate condition has been stereotyped and does not oscillate from 

 one side to the otheT^hen the position of the viscera is reversed. 



As I shall presently show, there are grave difficulties in the way of 

 accepting this view — the one fact that in the anthropoid apes the 

 viscera are placed as in man, the centre of gravity being to the right 

 of the mesial line, while in them right-handedness has not been 

 developed to the same degree as in man, is enough to negative it ; 

 but even if we did accept it, it would not finally solve the problem 

 of right-handedness, but only postpone the solution, or carry it a step 

 further back, for if we admit that right-handedness took origin in 

 bodily preponderance on the right side, we must next ask how did 

 this bodily one-sidedness arise ? How comes it that the heart is on 

 the left side and the liver on the right in an enormous majority of 

 human beings, and that in a few exceptional cases, analogous to but by 

 no means coincident with cases of lef t-handness, they are transposed ? 



It is not in the configuration of the body, nor in any individual 

 functional habit dependent thereon that the cause of right-handedness 

 is to be sought, but in the structure and organisation of the brain 

 that initiates, directs and controls all voluntary movements. The 

 brain has two hemispheres, presiding over the two halves of the body, 

 and its action is crossed, the right hemisphere presiding over the left 

 half of the body and the left hemisphere over the right. It has long 

 been clear to investigators that the functional differences in the two 

 hands must be in some way connected with differences in the two 

 hemispheres, and the first difference that suggested itself was one of 

 size. ^ It was thought that probably the left hemisphere was larger and 

 heavier than its companion on the right, and so supphed more energy 

 and therefore determined the superiority of the right arm and hand. 

 Measurements for a time seemed to corroborate this supposition. Dr. 

 Boyd weighed the hemispheres separately in 200 patients dying in the 

 Marylebone Infirmary, and found that "^almost invariably the weight 



Vol. XYIII. (No. 101) 2 t 



