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122 HUNTER ON THE TEETH.
In this enquiry, to avoid confusion, 1 shall confine the
description to the Teeth in the Lower-Jaw ; for the only diffc-

observations of Goodsir, as has been already stated, the ten anterior
permanent teeth in each jaw are formed in cavities of reserve behind
the follicles of the ten milk teeth, whilst the three permanent molars
on each side are formed in posterior cavities of reserve, formed by pro-
longations backwards of the primitive dental groove. About the
fourteentli week, behind each milk follicle a small lunated recess,
similar to an impression made by the nail, is said to be formed. These
depressions escape the general adhesion of the sides of the dental groove,
but by the closure of the latter they become converted into cavities,
which are formed successively from before backwards, and ultimately
become the sacs for the incisor, canine, and bicuspid teeth. These
cavities elongate and sink into the substance of the gum, above and
behind the upper milk follicles, below and behind the lower. A papilla
is formed at the bottom of each, that for the central incisor appearing
first, about the sixth month. Opercula, as is alleged in the case of the
temporary teeth, are developed from the sides of the sac, dividing it
into two portions, the lower of which encloses the papilla, which becomes
the pulp of the permanent tooth. The upper and narrower part of the
cavity becomes gradually obliterated by the adhesion of its sides. The
permanent sac then adheres to the back of '.hat for the temporary tooth.
Both grow, and after a time it is found that each sac (the permanent and
temporary) becomes lodged in a separate osseous recess or socket—that
for the permanent tooth in the lower jaw being below and behind that
for the temporary, in the upper jaw above and behind. A bony par-
tition separates them. The permanent sac and its osseous recess present
a pear-shape. The sac is connected with the gum by a solid mem-
branous pedicle, which is contained in an osseous canal, which opens
by an aperture on the edge of the jaw, behind the socket for the tem-
porary tooth. The permanent tooth is formed in its sac in the same
manner as the milk tooth, from which it is separated by a bony par-
tition. In the rise of the permanent tooth through the gum, it presses
on tlie bony partition and on the root of the milk tooth ; these latter
become absorbed under the influence of the pressure ; the milk tooth,
after the greater or less absorption of its fang, falls out, and the per-
manent tooth takes its place. A description of the formation of the
posterior cavities of reserve, and of the papilla of the true molars, has
already been given in the previous note on the dental pulps. (1) Vide
note v. p.
Kolliker gives, on the whole, a similar account of the formation of
the germs of tin- permanent teeth, lie observes, thai in the fourth

(1) Vide 'Quain's Anatomy,' by Professors Sharpey and Quain.