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Some of the features of the top portions of Figure 1 and Figure 2 were mentioned in discussing Table 1.

First, the Onset Profile spreads across approximately 12 years for boys and 10 years for girls.

In contrast, 20 of the 21 lines in the Completion Profile ( excluding center 5 for boys and 4 for girls ) are bunched and extend over a much shorter period, approximately 30 months for boys and 40 months for girls.

The Maturity Chart for each sex demonstrates clearly that Onset is a phenomenon of infancy and early childhood whereas Completion is a phenomenon of the later portion of adolescence.

Second, for both sexes, the 21 transverse lines in the Onset Profile vary more in individual spread than those in the Completion Profile.

Although the standard deviation values on which spread of the lines is based are relatively larger for those centers which begin to ossify early ( Table 1 ), there are considerable differences in this value between centers having the closely timed Onsets.

Third, the process of calcification is seen to begin later and to continue much longer for these boys than for the girls, a fact which confirms data for other groups of children.