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Page:Popular Science Monthly Volume 65.djvu/365

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361
DEXTRALITY AND SINISTRALITY.

phylogeny.' We can, therefore, never explain the phases of development through which an organism passes except by knowing the corresponding stages of evolution of the line of its ancestral forms. If, therefore, we ever solve the mystery of dextrality and sinistrality, it will be by the study of the conditions, habits, necessities, etc., of the ancestral types when dextrality and sinistrality arose. The infant of a few months shows no signs of preference in the use of the hands; it is not yet dextromanual, nor ambidextral; it is simply nondextrous, or ambisinistrous. Almost as soon as it exhibits any conscious effort toward skillful use of the hands it begins to show signs of dextromanuality. Before it walks, before it is one year old, dextrality is clearly pronounced. Baldwin (Pop. Sci. Mo., Vol. XLIV.) has demonstrated experimentally that it is plainly established as early as the seventh or eighth month. The period in phylogenous savage life to which this of the infant corresponds must, therefore, be that of the earliest phase of humanization. The animals, even the anthropoid apes, do not, so far as I have observed, exhibit it. Vierordt says that parrots grasp food with the left foot, by preference, and that lions strike with the left paw. Livingston is quoted as thinking 'all animals are left-handed' I suspect this is all error, because, as a rule, it would disadvantage rather than help in the animalian struggle.[1]

Since any sort of consciousness of the facts has existed the wisdom of dextromanuality has been emphatically exhibited: (1) In the word dexterity, which is the prized and honored quality of savage and civil-


  1. In the comparative absence of interest in these subjects there is a resultant dearth and awkwardness of words describing the conditions. It seems necessary to coin a few in order at least to avoid more cacophanous ones. The following, some of them already listed in the dictionaries, may be found useful in future discussions:

    Dextral, pertaining to the right side of the body.
    Sinistral, pertaining to the left side.
    Dextrality, Sinistrality, the corresponding abstract qualities.
    Dextrad, Sinistrad, toward the right, or left, respectively.
    Dextromanual, Sinistromanual, dextrality and sinistrality, respectively, as relating to the hands.
    Dextropedal, Sinistropedal, as relating to the feet.
    Dextrocular, Sinistrocular, as relating to the eyes.
    Dextraural, Sinistraural, as relating to the ears.
    Dextrocardial, Sinistrocardial, as relating to the heart.
    Dextrohepatal, Dextrosplenic, etc., may be formed.
    Dextrocerebral, located in the right cerebral hemisphere.
    Sinistrocerebral, located in the left cerebral hemisphere.
    Dextrorse, turned, turning, or moving to the right.
    Sinistrorse, turned, turning or moving to the left.
    Sinistrous, awkward, unskilled.
    Dextrous, skilled, expert.
    Ambidextrous, equally skilled with both hands.