Treatise Upon the Genesis and Development of the Dental Follicles to the Epoch of the Eruption of the Teeth. [Volume: 2, Issue: 9, April, 1861, pp. 475-486]

GENESIS AND DEVELOPMENT OF THE DENTAL FOLLICLES. 4'7

that which relates to the development of these parts of the follicles, with
that which concerns the tooth, as a resistant organ, having a crown or
exterior part, and a radical or deeper portion. It is an established fact
that each tooth once produced, as far as the ivory and enamel, follows a
method of evolution proper to itself, and as distinct from the manner of
development of the follicle, as the ivory is from the tissues which form the
follicle-this development differs in the teeth according to their size and
degree of complication. For example, in the calf, the crown is more
rapidly completed in the incisors than in the molars, which are larger and
more complex, notwithstanding the fact that the dentine appears in the
former a considerable time after it appears in the latter. Thus, among
calves, the eruption of the incisors is, nevertheless, commenced at birth
and completed in a month, much before the eruption of the molars.
Eruption is then a phenomenon, which is subordinated especially to the
development of the tooth as an organ, and is not in absolute connection
with the origin and development of the follicle itself. This phenomenon
is complicated, moreover, by all that belongs to the development and to
the atrophy of the maxillaries and gums, as is shown by the eruption of
the wisdom tooth. In consequence of this, the appearance of the teeth
does not occur in all animals in the same order as the birth of the follicles
to which they correspond. One of these phenomena cannot therefore be
judged strictly by the other.
On the contrary, the regularity with which the essential parts of the
follicle succeed each other, and complete their own development, according to the order of their first appearance, enables us, where several follicles are united side by side, to be certain that those most developed in
structure are the oldest, even when they are of less size than some of the
others.
In the practice of anatomy, accordingly, the one which appears first is
the only matter of difficulty in determining the precise period of the
appearance of the follicles. This point once fixed, the degree of advancement of those found at its sides at a subsequent period, is in itself sufficient to show the time of their origin in comparison with that of the first.
In the human foetus the follicles appear in nearly the same order as the
issue of the corresponding teeth, for each of the jaws considered individually. Thus, the follicle of the anterior molar and that of the internal
incisor appear at nearly the same time, and the dentine afterward shows
itself in both simultaneously. (Plate I. fig. 1, m m.) The external incisor follows them closely, the posterior molar comes a little later, and
the canine last; it continues for a long time situated on a plane, which is
nearer to the corresponding dental nerves and vessels than to the others.*

* According to Henle the follicles appear in the following order: anterior molar,
canine, internal incisor, external incisor, posterior molar; but this is not correct.