Page 139 - My FlipBook

OF THE FORMATION OF THE ADULT TEETH, ETC. L28
rence between those in the two Jaws, is in the time of their
appearance, and generally it is later in the Upper-Jaw. Their
formation and appearance proceeds not regularly from the first
Incisor backwards to the Dens Sapientta, but it begins at two
points on each side of both Jaws, viz. at the first Incisor, and
at the first Molaris. The Teeth between these two points make
a quicker progress than those behind.
The Pulp of the first adult Incisor, and of the first adult
Molaris begin to appear in a Foetus of seven or eight months,
and five or six months after birth the ossification begins in
them ; soon after birth the Pulp of the second Incisor and
Cuspidatus begin to be formed, and about eight or nine months
afterwards they begin to ossify ; about the fifth or sixth year
the first Bicuspis appears ; about the sixth or seventh the
second Bicuspis, and the second Molaris; and about the
twelfth, the third Molaris or Dens Sapicntim.ip)

month, the cavities containing the papilke of the temporary teeth become
narrower and narrower, and at length are perfectly closed, " but in such
a manner, that over each cavity, or tooth-sac, another small recess is
formed as cavity of reserve for the twenty anterior permanent teeth, of
which, even in the fifth month of icetal life, the tooth germs are de-
veloped. At first the new cavities lie over the tooth sacs of the milk
teeth, but they gradually move to the posterior side of them ; and when
the bony alveoli of the milk teeth appear, are received into small
dilatations of them, which, in the incisor and canine teeth, become at
last completely separate from the others ; in the two first molars (bicus-
pides), on the other hand, open at the bottom of the alveoli of the milk
teeth. The tooth sacs of all these teeth are drawn out at the apex in
form of a solid cord, which extends either to the gum or on the two
first molars (bicuspides), to the periosteum at the bottom of the two
milk molars, and which has been incorrectly considered as being a con-
ducting band (gubernaculum) of the teeth in their eruption. (1)"
Robin and Magitot deny that the follicles of the permanent teeth are
developed in depressions on the surface of the mucous membrane of the
gum.]
(b) [The papillae of the first true molars appear as early as the six-
teenth or seventeenth week according to Kolliker and Goodsir ; some-
what earlier—the eighty-fifth to the ninety-fifth day—according to Robin
and Magitot. Kblliker, as before noticed, states that the tooth genus of the
(1) Kolliker, op, oit., p. 301.