The Growth of the Spinal Axis of the Human Body in Prenatal Life.

Abstract

It has been previously pointed out^{1, 2, 3} that the growth of the external dimensions of the human body in the fetal period is directly proportional to the growth in length of the body as a whole. The same law holds true for many of the lineal dimensions of the internal organs and parts, and is particularly well illustrated by the growth of the spinal column in prenatal life.

We have studied these relationships by measurements of the total length of the spine and its parts in 148 specimens ranging from 2.5 to 55.0 cm. in total or crown-heel length, and have placed the results in the form of empirical formulae. These formulae were computed from the mean spine lengths for 5 cm. intervals of crown-heel length by the method of averages, weighting by the square root of the number of cases in each interval.

In all instances we have found that the relationship of the spine and its parts with the total body-length is a rectilinear one which may be represented by the expression:

where “S” is the length of the spine or any spinal segment, “L” is the total body-length and “a” and “b” are empirically determined constants.

The growth of the total spine is illustrated by the upper curve in figure 1 and may be expressed by the formula :

The calculated means of the spine length, as determined by this formula, show a mean weighted absolute deviation of 1.37 mm. from the corresponding observed averages, for the 5 cm. intervals of crown-heel length, which is approximately the same as the mean of the probable errors of these observed averages. The mean, weighted, relative deviation of the observed from the calculated values is 1.29 per cent.