Why is a particular child right-handed or left-handed? / by George M. Gould.

  • Gould, George Milbrey, 1848-1922.
Date:
1907
Catalogue details

Licence: In copyright

Credit: Why is a particular child right-handed or left-handed? / by George M. Gould. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    [Reprinted from Long Island Medical Journal, November, 1907]. J2P WHY IS A PARTICULAR CHILD RIGHT-HANDED OR LEFT-HANDED ? By GEORGE M. GOULD, A.M., M.D., PHILADELPHIA, PA. IF, as I believe, the study of civilized people shows that the special inci- dence of right-handedness, and of left-handedness, and of mixed types, is governed directly by ocular domi- nance, and only indirectly and partial- ly by heredity, a thorough understand- ing of the subject will be gained by a preliminary look at the precedent ani- mal function and habit. And this is epitomized as right-eye dominance of general dextral or right-side function, and left-eye dominance of general sin- istral function. To begin with, em- bryology demonstrates the existence of vision long before muscles, so that historically and evolutionally vision governs motility; the very cleavage of the brain in the two so independent halves of all types was doubtless due to the unilateralism and independence of ocular function. The more primi- tive the type the more on one side of the head was the governing eye, and the more independent it was of its fel- low upon the other side. A motion to strike one eye from its side does not cause the other eye to wink or to pro- tect itself or the animal from injury. One eye governed one side of the body (because vision must incite and con- trol all action), especially the co-ordi- nated front foot of that side, but also the hind one of that side to a less de- gree or less accurately; and the other eye acted for the other lateral organs in the same way. Fewer and less ac- curately co-ordinated commissural fibers between the two hemispheres were then necessary than when later complication and specialization arose. It is evident that when one eye was placed upon one side of the head, not looking forward, and separated from the other by a protruding mass of or- gans and bony structures, it must act independently of the other, to see ob- jects upon that side of the body, to protect it, and to govern the muscles of its side. So long as the forefeet are equally used, i. e., so long as no differentiation of their function arises, there can be no question of the exist- ence of right-handedness, or right- footedness. The chief, most frequent, most necessary of all animalian four- footed function is placing first one front foot, and then the other front foot, in the safe and right place and position, especially in rapid motion, fighting, defence, etc., etc. That plac- ing of the right forefoot must be dominated by the right eye, and of the left forefoot by the left eye. There is simply divided dominance of the eyes, each supreme in the control of its cor- related lateral organs. The peculiari- ties of the avoidance by a horse of a stone or log in the road, by, say, the right hind foot, the stone at the in- stant out of sight, and the right eye perhaps governing the avoidance of a similar impediment in front by the right forefoot, is a most instructive thing. The co-ordination of eye and front foot is more exact, and the very awkwardness of the hind foot is sig- nificant. The approach toward binocularity, the advance of the eyes toward the front of the skull, the degree of for- ward-lookingness, if one may so speak, is measured and indicated by the prog- ress toward parallelism of the ocular axes. Recapitulated, this progress to- wards parallelism is steady from lower to higher types, reaching complete parallelism only in man. In the most civilized of humans, the literary and handicraft workers, the progress does not end with parallel- ism, but the ocular axes must be sharply converged upon a point 12 or 15 inches from the eyes for ten or