Page 128 - My FlipBook

112 HUNTER ON THE TEETH.
deeper, its mouth also grows narrower, and at length is almost
but not quite, closed over the contained Tooth.
The disposition for contracting the mouth of the cell, is

at intervals by little vertical projections, which stand facing each other
on each side. These projections increase, and ultimately join each other,
forming complete partitions, which divide the groove into cells, or
alveoli. In Man, this takes place at an advanced period of gestation.
As late as the ninth month of foetal life, the contents of the groove can
be raised in one piece. The partitions bridge over the lower part of the
groove containing the dental vessels and nerves. The rudiments of the
partitions always unite, in the first place, between the first molar and
the canine, and then between the latter and the second incisor. The
rudiments of the first partition join to form a narrow, slender, and
thin lamina, passing over the nerves and vessels at the bottom
of the groove towards the end of the fourth month. The prolonga-
tions between the canine and second incisor become united near the
sixth month. They unite between the two incisors near the
seventh month, but not between the molars until after birth. Before
the projections unite throughout their whole height, they form a very
slender bridge immediately above the vessels. This bridge grows in
height by prolongations from the walls of the groove. The partitions
are not completed until after birth. The following is the account given
by the same observers of the formation of the alveoli in the upper jaw.
About the fifty-fifth day (in the human subject) there appear at the
outer edge of the superior maxillary bone two thin crests, an external
and an internal one ; these crests limit a groove, which has at first the
appearance of a shallow furrow. Shortly after, a similar groove is
formed in the same manner upon the inter-maxillary. In the posterior,
two-thirds of the groove in the superior maxillary, the suborbital vessels,
and nerves are lodged. The external lip of the dental groove passes
above them, near its anterior extremity, in order to allow them to reach
under the skin. " This groove is thus produced immediately below the
eye, a place occupied at that time by the edge of the upper maxillary,
and which the nerves and vessels continue to occupy. The same thing
occurs in the lower maxillary, where the groove appears before that of
the other jaw. The groove of the upper maxillary is common to the
dental follicles, which are about to appear, and to the vessels which
remain suborbital." The bottom of the groove becomes in the course
df development the suborbital canal, just as in the lower maxillary
it becomes the dental canal, but the separation between the canal and
the groove takes place much sooner in the superior than in the inferior
maxilla. "Nevertheless, it is at the bottom of this groove, against the
suborbital nerves and vessels, and consequently in the part which after-
wards becomes the suborbital canal, that the dental follicles also