Treatise Upon the Genesis and Development of the Dental Follicles to the Epoch of the Eruption of the Teeth. [Volume: 2, Issue: 1, August, 1860, pp. 3-10]

6

THE DENTAL COSMOS.

fore and during the evolution of the follicles. We have found that it is
impossible to comprehend fully the description of that evolution without
a previous knowledge of these changes. The consideration of these has
led us to treat in this chapter: First, the order in which the various parts
that constitute the jaws appear; second, the jaws before the appearance
of the dental bulbs; third, the jaws at the time of the origin of the follicles. Each of these subjects will be considered in a separate paragraph.
~ 1. The order of the appearance of the various constituent parts
of the jaws.-The two jaws originate with the aid and at the expense of
the first embryonic visceral arch; this is also the case with the soft parts
that accompany them. They appear under the form of papillae or bourgeons, (called maxillaries by M. Coste, in accordance with that which is
learned from their ulterior evolution.) These bourgeons (sprouts) are
situated underneath the embryonic encephalic mass or cerebral capsule.*
In the human fcetus at 15 or 18 days, the lower jaw is represented by two
small tubercles, which are the tongues of origin of the principal part of the
first visceral arch. The superior maxillary bourgeons, less advanced than
the preceding, are placed upon the sides and a little higher than the embryonic frontal apophysis or prolongation of the anterior cerebral cell.
They are a dependency and a prolongation of the external side of the
base of the tongues, or inferior maxillary bourgeons, and are consequently
part of the first visceral arch.
Toward the 25th or 28th day, the embryo being nearly thirty millimetres (1'18 inch) in total length, the inferior maxillary bourgeons are
united upon the median line; and the superior bourgeons, always isolated, have descended to the level of notch of the frontal apophysis.
* It is known that since Rathke, (1826,) the name of branchial or visceral arches has
been given to some transitory embryonic organs disposed under the form of arches
at the anterior or cephalo-cervical extremity of the embryonic vertebra; they are five
in number in birds, and four in the mammifera, and are superposed from below the
cerebral capsule to the level of the heart. They are contiguous, but distinct and narrow slits, called branchial or visceral slits, can be seen between them. It is by the aid
and at the expense of their tissue that the different sub-cranial organs of the face and
all those of the neck successively originate. They appear, one after the other, from
the top downward, as soon as the cephalic extremity of the embryo is separated
from the blastoderm, and under the form of bourgeons or tongues (at the blunt extremity) which proceed from the base of the cerebral capsule as soon as the visceral
or ventral lamine of the body of the embryo are closed. These to2ngues, called branchial or visceral, converge at each side below the cerebral capsule toward the median
line, and it is in uniting that they form arches; at the same time the ventral laminse
disappear at this level. The first arch is the largest, the second a little less, as are
likewise the others, which show themselves when the first have already commenced
to give origin to definite organs. One of the authors of this treatise has frequently
proved that they are not formed by the embryonic cells, but by the embryo-plastic
nuclei, and are covered by a unique range of epithelial mosaic-like cells.