LEFTHANDEDNESS. 477 



folds of tlie cei'ebral mass in its later development in the osseous 

 chamber of the skull; and within ordinary limits they probably exer- 

 cise no appreciable influence on physical or mental activity. From 

 long and careful observation, especially of children, I am satisfied 

 that -with the great majority righthandedness is mainly the result of 

 education, or a compliance with prevailing usage. Little efibrt 

 would be needed with such to superinduce lefthandedness. But 

 there are a sufficient number of persons naturally and instinctively 

 righthanded to determine the bias of the majority ; though they 

 cannot influence another, though smaller number, who have an equally 

 strong and ineradicable impulse to the use of the left hand. Wherever, 

 therefore, opportunity is afibrded for examination of the brain, it is 

 desirable that in every case of marked inequality between the two 

 hemispheres, inquiry should be instituted as to the concurrence of a 

 strongly pronounced right or lefthandedness. 



But it has also been affirmed as the result of repeated observations, 

 that there is often a decided diflierence in the weight of the two 

 hemispheres of the brain. M. Broca states that in forty brains he 

 found the left frontal lobe heavier than the right ; and Dr. Boyd, 

 when describing the results obtained by him from observations on 

 upwards of 500 brains of patients in the St, Marylebone Hospital, 

 says : " It is a singular fact, confirmed by the examination of nearly 

 200 cases at St. Marylebone, in which the hemispheres were weighed 

 separately, that almost invariably the weight of the left exceeded 

 that of the right by at least the eighth of an ounce." But the care- 

 ful independent observations of Professor Wagner and Dr. Thurnam 

 failed to confirm these results. From the weighing of the two 

 hemispheres of eighteen distinct brains, Professor Wagner found the 

 right hemisphere the heavier in ten, and the left in six cases, while 

 in the remaining two they were of equal weiglit. Dr. Thurnam, 

 without entering into details, states that the results of his weighings 

 did not confirm Dr. Boyd's observations ; adding that " fresh careful 

 observations are certainly needed before we can admit the general 

 preponderance of the left hemisphere over the right." 



It has to be borne in remembrance that though the two hemi- 

 spheres of the brain are sufficiently indicated in every case, there is 

 no natural separation between them, and the division in the exact 

 median line is a delicate operation, in which a very slight bias of the 

 operator's hand will suffice to beget such a deviation from the true 



