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THE MANNER IN WHICH A TOOTH IS FORMED. 127
then a complete set comes in both Jaws. I never saw an in-
stance of this kind but once, and there two fore Teeth shot up
in the Lower-jaw.
I should suppose that a now Alveolar Process must be also
formed in such cases, in the same manner as in the production
of the first and second sets of Teeth. From what I can learn,
the age at which this happens is generally about seventy.
From this circumstance, and another that sometimes happens to
women at this age, it would appear that there is some effort in
nature to renew the body at that period.
When this set of Teeth which happens so late in life, is not
complete, especially where they come in one Jaw, and not in
the other, they are rather hurtful than useful ; for in that case
we are obliged to pull them out, as they only wound the
opposite Gum. (
The body of the Tooth is formed first, afterwards the Enamel
and Fangs are added to it. All the Teeth are produced from a
kind of pulpy substance, which is pretty firm in its texture,
transparent, excepting at the surface, where it adheres to the
Tlie order of eruption of the permanent teeth in the anthropoid apes
presents a remarkable contrast to their sequence in man. Professor
Owen remarks : " Both Chimpanzees and Orangs differ from the human
.subject in the order of development of the permanent series of teeth ;
the second molar (m 2) comes into place before either of the premolars
has cut the gum, and the last molar (?h 3) is acquired before the canine.
We may well suppose that the larger grinders are earlier required by the
frugivorous Chimpanzees and Orangs than by the higher organised omni-
vorous species with more numerous and varied resources, and probably
one main condition of the earlier development of the canines and pre-
molars in man may be their smaller relative size. (1)]
(d) [Many of these cases are doubtless instances of retarded eruption.
A tooth which has been retained at length becomes exposed by the ab.
sorption of the superjacent gum.]
(1) Owen, Art. Odontology, Encyc. Brit. 8th Edit.
