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OF THE FORMATION OF TEETII IN THE FCETUS. 110
OF THE FORMATION OF THE TEETII IN THE FCETUS.
The depression, or first rudiments of the Alveoli observable
in a Foetus of three or four months, is filled with four or five
little pulpy substances, which are not very distinct at this nge.(r)

over the back part of the crown, to the extent of one-fourth of its
antero-posterior dimensions. On the upper surface of this, within a
line of its edge, a depression in the bone may be seen. This is a com-
mencement of a crypt for the second permanent molar. The corre-
sponding teeth of the superior maxillae occupy the tuberosity, the
posterior part of which is extremely thin, and in the median line im-
perfect. This gives a long and curved opening to the socket, and a
posterior direction to its further half. In the upper jaw we have, as yet,
no indications in the bone, of preparations for the lodgement of the
second permanent molar." (1) At the age of forty months, the opening
of the crypt of the first upper permanent molar has become smaller,
and is directed downwards instead of downwards and backwards.
Behind it on the posterior surface of the tuberosity is a depression
marking the commencement of the crypt for the second permanent
molar. Nine months later, the crypts for the second permanent molars
have become larger, with well-defined margins. " In the upper jaw
they look backwards towards the pterygoid plates of the sphenoid ; in
the lower, upwards and a little inwards, their floors lying immediately
over the inferior dental canal, near its commencement." About the age
of seven years, when the first permanent molars have gained the level
of the temporary teeth, the second upper molars, which at first were
directed backwards, now begin to descend into the dental line, and are
directed obliquely downwards and backwards. Between the age of
twelve and thirteen, the second permanent molars are advancing towards
the surface of the gums, and the crypt for the third molars hold the
positions which those for the second occupied when the first molars were
emerging from the alveoli. (2) ]
(y) [The dental pulps or bulbs. Two opinions are current with respect
to the mode of origin of the dental pulps which may be here briefly
stated. One is that the dental pulp commences as a papilla on the free
siu-face of the mucous membrane covering the edges of the maxillary
arches. This is held by Arnold and Goodsir, who came to their con-
clusions independently of each other. The other is that the dental pulp,
together with the follicle in which it is afterwards contained, and the
"enamel organ," have their origin in the submucous tissue which fills
the groove in the maxillary. This opinion is sustained by the researches
of Robin and Magitot.
(1) Tomes, Op. tit., p. 30.
(2) Tomes, Op. cit. , pp. 5—103.