Page 127 - My FlipBook

OF TIIE FORMATION OF TIIE ALVEOLAR PROCESS. Ill
In the Lower-Jaw the vessels and nerves run along the
bottom of this Alveolar cavity, in a slight groove, which after-
wards becomes a complete and distinct bony canal.
The Alveolar Process grows with the Teeth, and for some
time keeps the start of them. The ridges which arc to make
the partitions shoot from the sides across the canal, at the
mouth of the cell, forming hollow arches : this change happens
first at the anterior parts of the Jaws, (s) As each cell becomes
(s) [A very lull description of the formation of the alveoli is given by
Drs. Robin and Magitot, in their " Treatise on the Genesis and Develop-
ment of the Dental Follicles." According to these observers, the first
traces of ossification in the lower jaw appear near the middle of the
inferior maxillary cartilage ; they are elongated in form, and show
themselves about the thirty-fifth day of intra-uterine existence. The
ossifying process rapidly invades the whole cartilage. Two very thin
ridges then appear on the upper margin of the bone ; these ridges do
not exist in the cartilaginous state, but are formed according to the
mode of ossification called " invasion." At an early period, they give
the bone the appearance of being formed by two parallel osseous bands.
These ridges limit the groove in which the dental follicles originate.
The groove extends from the anterior edge of the ascending branch of
the maxillary, encroaching a little on its inner face, as far as the anterior
extremity of the corresponding branch of the maxillary ; consequently,
the whole of its contents can be removed in one piece. The groove is
of considerable depth. In Man, the solid part of the bone, from the
canine as far as the symphisis, becomes higher than the groove is deep
about the beginning of the fourth month. At the level of the molars,
and in relation to the axis of the lower maxillary, the groove is situated
inside the latter, but passes round it, in order to be continued on the
side of the outer face in the whole portion containing the follicles of the
canine and the incisors. The groove is widened, as if swollen in blisters
about its posterior third, narrow in front, and more suddenly contracted
behind. It opens at the inner face of the ascending branch of the
maxillary by a fissure-shaped opening, broadened and rounded at the
level of the bottom of the groove, and narrow above, where it soon
closes ; there then remains only the lower part of the slit which forms
the posterior dental foramen, or posterior orifice of the dental canal,
which is traversed by the vessels and nerves of the same name ; they
make part of the contents of the groove. The dental vessels and nerves
are contained in a slight furrow at the bottom of the groove. The
furrow is smooth and regular, and, at a later period, becomes the dental
canal. From the time of the genesis of the dental follicles, the inner
surface of each lamina forming the sides of the groove becomes thickened