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cisores and cuspidati, which are much larger than their pre-
decessors, to become regular, without any increase of the
arch or circle. He was led into this opinion by comparing
four lower jaws of different subjects, and at different periods
of life ; from the age when the five temporary teeth are
completed, to that of the entire permanent set. He ac-
knowledges, however, that it is impossible there should be
a mathematical exactness in four different jaws ; nor indeed
is there a mathematical exactness in the lines drawn to sup-
port his theory, for they are by no means parallel.*
Indeed so varied are the dimensions of jaws, that the arch
of one a year old may correspond, or even exceed the arch
of an adult ; and vice versa, the arch of an adult may be
nearly as large again as that of a child ; so it is not by com-
paring different jaws together that we shall be enabled to
draw proper conclusions ; but by comparing the permanent
and temporary teeth of the same jaws.
It appears from my preparations, and experience convin-
ces me, that the space occupied by the temporary teeth
would not be sufficient to accommodate the same number of
permanent teeth which succeed them, and which on the
whole are so much larger, particularly in the upper jaw.
This fact Mr. Hunter was aware of, and mentions that irreg-
ularities are more frequently met with in the upper, than in
the lower jaw ; so far I agree with him.
We have seen the rudiments of the permanent teeth at
first placed nearly regular, but as ossification advances on
them, they become crowded together for want of room.
This irregularity particularly happens to the permanent teeth,
because they are at first situated at the internal part of the

* Nat. Hist. Plate 16, Figure 2.