EIGHTHANDEDNESS. 203 



the posterior lobes. Hence, in consequence of the well-known decus- 

 sation of the nerve-roots, the right side of the body — so far as it is 

 influenced by brain-force, — would, in early foetal life, be better supplied 

 with nervous force than the left side; and thereby movements of the 

 right arm would precede and be more perfect than those of the left. 

 But the premises of Gratiolet are disputed ; and even if proved, they 

 must raise further questions, not merely as to the origin, but also as to 

 the influence of such an unequal development of the brain on the action 

 of the limbs. 



Professor Buchanan, of Glasgow, resorts to a difi"ereat theory to 

 account for righthandedness.* According to him, " The preferential 

 use of the right hand is not a congenital, but an acquired attribute of 

 man. It does not exist in the earliest periods of life." Nevertheless, 

 " no training could ever render the left hand of ordinary men equal in 

 strength to the right;" for "it depends upon mechanical laws arising 

 out of the structure of the human body." This theory is thus 

 explained : In infancy and early childhood, there is no difference in 

 power between the two sides of the body ; but so soon as the child 

 becomes capable of bringing the whole muscular force of the body into 

 play, " he becomes conscious of the superior power of his right side — 

 a power not primarily due to any superior force or development of the 

 muscles of that side, but to a purely mechanical cause. He cannot put 

 forth the full strength of his body without first making a deep inspira- 

 tion ; and by making a deep inspiration, and maintaining afterwards the 

 chest in an expanded state, which is essential to the continuance of his 

 muscular effort, he so alters the mechanical relations of the two sides of 

 his body, that the muscles of his right side act with a superior efficacy ; 

 and, to render the inequality still greater, the muscles of the left side 

 act with a mechanical disadvantage." Hence the preference for the 

 right side whenever unusual muscular power is required, and with the 

 greater exercise of the muscles of the right side, their consequent 

 development, until the full predominance of the right side is the result. 



This theory is based, not merely on the disposition of the lungs on 

 the right side, but on these further facts : that the right lung is more 

 capacious than the left, having three lobes, while the left has only two ; 

 that the liver, the heaviest organ of the body, is on the same side ; 



* Mechanical Theory of the Predominance of the Right Haad over the Left ; or, more gene- 

 rally, of the Limbs of the Kight Side over those of the Left Side of the Body. By Ajidrew 

 Buchanan, M.D., Professor of Physiology in the University of Glasgow. 



