478 LEPTHANDEDNESS. 



line as would fully account for the conflicting results referred to. 

 On tlie assumption that right and lefthandedness are traceable to 

 the relative development of the two hemispheres of the brain, the 

 results very well accord with actual manifestations. There is a 

 noticeable excess in the examples of greater weight of the left than 

 of the right hemisphere ; but apparently a still larger number of 

 cases are to be found where it is diflS.cult to determine any noticeable 

 bias either way. But other observers have assigned much more com- 

 prehensive functions, and a nearly independent action, to the two 

 hemispheres of the brain. 



Dr. Brown-Sequard, who strongly favours the idea of the supe- 

 riority alike in size and weight of the left over the right hemisphere, 

 reverts to an argument derived from lefthandedness when discussing 

 his theory that the two hemispheres practically constitute two distinct 

 brains, each sufiicient in itself for the full performance of nearly all 

 mental opei'ations, though each also has its own special functions, 

 among which is the control over the movements and the organs of 

 opposite sides of the body. " Every organ," he says, " which is put 

 in use for a certain function gets developed, and more apt or ready 

 to perform that function. Indeed, the brain shows this in point of 

 mere size ; for the left side of the brain, which is used most, is larger 

 than the right side. The left side of the brain also receives a great 

 deal more blood than the right side, because its action preponderates ; 

 and every organ that acts miich receives more blood." He accord- 

 ingly affirms that the growth of the brain up to forty years of age, 

 if not indeed to a considerably later period of life, is sufficiently 

 marked to require the continued enlargement of the hat. Speaking 

 of himself, as having then passed his fifty-sixth year, he says : — 

 " There is no period of six months that has passed that I have not 

 found my hat, if neglected and put aside, has become too small. 

 The head, growing is very strong proof that the brain grows also." 

 The opinions advocated by the leading anatomists of Europe in the 

 earlier years of the present century, difiered widely from this. , It 

 was indeed maintained by Soemmering, the Wenzels, and Tiedemann, 

 that the brain attained its greatest development not later than at 

 seven or eight years of age. But, without going so far as Dr. Brown- 

 Sequard is prepared to do, the old idea as to the complete develop- 

 ment of the brain in. youth is now abandoned, and the latest observers 

 have produced evidence in proof of the brain increasing in weightj 



