Abstract
It has been pointed out by Calkins, 1 Calkins and Scammon 2 and others 3 that the growth of a large number of the external dimensions of the human body in the fetal period is directly proportional to the growth in total body-length, and that the probable values of these dimensions in this period may be expressed by the general formula:
where “D” is the dimension in question, “L” is the total body-length, “a” is a constant in the form of a decimal fraction, and “b” is a second constant in the form of an absolute number. In accord with the law of developmental direction the “b” constant is positive for dimensions of the head and neck, negative for dimensions of the extremities and positive, negative or zero for measurements of the trunk, depending on their position.
If this law holds true for all external bodily dimensions the volumes of the major body-parts should bear a similar relation to the volume of the body as a whole, or:
where “Pv” is the volume of any major body-part, “Bv” is the total volume of the body, and “a” and “b” are constants as in (1). In spite of the small differences in the specific gravity of the various parts of the body in prenatal life, the same relation should be approximated by the weights of the body and its various parts.
It is possible to test these relations with a series of observations by Corrado 4 which has not ken analyzed hitherto. These data include 137 observations on the weight of the head (and neck), and total body-weight for specimens ranging from 400 to 4000 gm. in body-weight.
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