There is no system in which anatomists have traced in a more accurate
manner than in this, the different states in the different periods of
life. The remarkable difference of a bone examined in the first months
when gelatine almost alone composes it, compared with a bone of an
adult in which the calcareous substance predominates, has especially
arrested their attention upon this point. Let us examine the phenomena
of ossification in all the ages; these phenomena should be considered
during and after growth. In general, while this continues, there are
some portions of the osseous system not ossified, as the neck of the
femur, for example; ossification is not complete, the bones are not
perfectly developed until towards the sixteenth or eighteenth year, and
sometimes even later.