456 GENERATION. 



Dextral Preeminence. The curious fact, that most per- 

 sons by preference use the right arm, leg, eye, etc., instead 

 of the left, while, as exceptions, some use the left in prefer- 

 ence to the right, has excited a great deal of discussion, even 

 among the earlier writers. There can be no doubt with re- 

 gard to the fact of a natural dextral preeminence ; and, also, 

 that left-handedness is congenital, difficult, if not impos- 

 sible, to correct entirely, and not due simply to habit. It 

 would appear that there must be some condition of organiza- 

 tion, which produces dextral preeminence in the great major- 

 ity of persons, and left-handedness, as an exception ; but what 

 this condition is, it is very difficult to determine. Several years 

 ago, J. Achille Comte proposed the theory that, in the most 

 common position of the foetus in utero^ the left side of the 

 body is pressed against the spinal column of the mother, and, 

 as a consequence, the muscles of that side are not so fully 

 developed as upon the right side. To carry out this explana- 

 tion, it would be necessary to show that, in the position in 

 which the right side is toward the back of the mother, the 

 individual is left-handed. Comte has endeavored to show 

 this, but his cases are not sufficiently numerous and clear to 

 carry conviction. 1 Another explanation, very often offered 

 by anatomists, is, that the right subclavian artery arises nearer 

 the heart than the left, that the right arm is therefore better 

 supplied with arterial blood, develops more fully, and is, con- 

 sequently, generally used in preference to the left ; but we can- 

 not explain the exceptional predominance of the left hand by an 

 inversion of this arrangement of vessels. The idea advanced 

 by Dr. D wight, of Boston, that " one-half of the brain (the 

 left) has a more acute perception of tactile impressions, while 

 the other (the right) distinguishes more readily different de- 

 grees of temperature and weight," is based upon a few ob- 

 servations on these points in right-handed persons and one 



1 J. ACHILLE COMTE, Recherches anatomico-physiologiques, relatives d la pre- 

 dominance du bras droit sur le bras gauche. Journal de physiologic, Paris, 1828, 

 tome viii., p. 41, et seq. 



