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THE ORIGIN AND FORMATION

DENTAL FOLLICLE.

TIIK FIRST MEMOIR ON THE

DEVELOPMENT OF THE TEETH.

DRS. III. LKGROS AND E. MAGITOT.

A TRANSLATION FROM THE FRENCH, WITH INTRO-
DUCTION AND NOTES,

By M. S. DEAN.

Authorized and REVIEWED r.v Dr. Magitot. the
Surviving Author.

Including all the Illustrations of tue French Work, with a
number op Additional Illustrations, Selected and Obiginax

I'll [C LGO:
JANSKN. McCLURG LND COMPANI

1880.

L SV-

^ — obu *

Copyright, 1879,
By M. S. DEAN.

"KNI3HT~t'.~LESNARD I

TRANSLATOR'S PREFACE.

AN apology will reasonably be expected for pre-
-Ol. seuting this translation to the profession.
It will require but few words, and I cheerfully offer
it. The deficiency and inaccuracy of the litera-
ture, in our own language, on the origin and de-
velopment of the "tooth-germ" and its associate
parts, render it almost worthless, as compared with
the more recent researches of foreign investigators.
The only exception I would make is that of the
valuable work of Professor Tomes. If anything
more is required, I refer the reader to the follow-
ing pages, which, so far as I have been able to do
justice to the authors, will be their own apology.

Some of you will remember that, nearly twenty
years ago, one of the authors of this memoir, Dr.
Magitot, in connection with Dr. Ch. Robin, wrote
a treatise entitled, The Genesis and Development of
the Dental Follicle, to the Epoch of the Eruption of
the Teeth, a large portion of which was translated
for the Dental ( 'osmos.

While the writers of that treatise gave a detailed
and elaborate account of the development of the
jaws and their anatomical constituents, that por-
tion devoted to the origin and formation of the
dental follicle was in many respects incomplete,
and in some particulars erroneous.

The improved methods of preparing sections
for microscopic examination which have since been
adopted, together with the experience gained by
many years of study, which one of these authors
has since devoted to this and kindred subjects, has
enabled him, with the aid of his eminent colaborer,
not only to correct the errors of that work, but
also to describe these parts more minutely, and
with greater exactness than had been hitherto pos-
sible.

While the present work traverses a portion of
the ground gone over by the previous writers, it is,
nevertheless, a distinct memoir, rendered more
comprehensive, and more complete in detail, by
the study of the development of the dental system
not only in man, but in many other mammifera.

Although the work may not be considered as a
" practical treatise," in the ordinary acceptation of
the term, yet it contains valuable lessons which
may be applied in preventing the disastrous con-
sequences of those exanthematous diseases which
are so liable to arrest or pervert the nutritive sup-
ply to these developing organs, and which often
result in the disfigurement, and sometimes in the
entire loss, of the teeth. Hence its suggestions
should not be confined to the dental surgeon alone,
but should be made available by the medical prac-
titioner, who, at the present day, retains almost
undisputed possession of this sadly neglected field
of practice.

The illustrations, including copies of all those
contained in the original, were executed by Baker

TRANS! vrm: - PREF \« I . 0

,i ' .. of thie city ; and. while all of them, I think.
compare favorably with the woodcuts found in
similar works. — sonic of them showing the minute
detail of the parte during the different stages of
development, — are remarkably faithful to nature.

How well the work of the translator has been
don.- niusi be loft for others to decide. It may be
proper to state, however, that it lias hem submitted
to Dr. Magitot, and meets with his unqualified ap-
proval.*

The conversational style in which many of the
notes have been introduced, may be regarded by
some as unsuited to the character <>( a severely
scientific work. However this may he, it certainly
affords the translator opportunities of presenting,
in an easy and familiar manner, the views of dif-
ferent authors, and some other valuable matter,
which he believes could not otherwise he intro-
duced without apparent abruptness. He believes,
also, that the plan here adopted will relieve the
monotonous strain upon the less scientific reader.
and that the facts thus brought out will be more
vividly impressed upon most minds than if pre-
sented in the ordinary way. If this be so, no other
defense is necessary.

The adjectival terms denoting the species of
embryos — as equine, bovine, etc.. and correspond-
ing to that of human — which have been adopted

* Extract from his letter. Paris, Sept. 8, L879: "Jt trouvt
eette traduction parfaite, et je reconnais <\>t> voire "Trans-
lator's Introduction' est tris ingenteust i»>">- preparer i<
r i' V intelligence <lu mimoin ."

6 teanslatoe's peeface.

in the translation, I think, cannot be regarded
with disfavor; the propriety, if not the necessity,
of their employment in works of this kind seems
to me unquestionable.

My labors upon this work have been light-
ened by the encouraging words of many leading
members of the medical, as well as the dental, pro-
fession; and to my esteemed friend and eminent
fellow-practitioner, Dr. G-. II. dishing, I am in-
debted for much kind assistance in preparing this
treatise for publication. And especially to Dr.
Magitot, the illustrious author of many scholarly
contributions to science, I must offer my grateful
acknowledgments for the cheerful aid he has so
promptly rendered me in the execution of this
work.

M. S. D.

34 Monroe Street, Chicago:
October, 1879.

CONTENTS.

TAOE

Translators Introduction, - 9

S I. Mucous Membrane, ... 9
§ II. Meckel's Cartilage and Development of the

Jaws, - ~"

§111. Intermaxillary Bones, - - - 38

§ IV. Definition of Terms, - - - 41

Authors' Introduction, - - - - 47

CHAPTER I.

Condition of the Jaws of the Embryo at the period of
the Genesis of the Follicle — The Epithelial Ridge
(Bourrelet), 48

ClIAITKi: II.

Epithelial Lamina, and the Genesis of the Enamel-
organ. -

62

CHAPTER III.

Origin and Formation of the Dental Bulb and of the
Follicular Wall (Sac), - !,:!

CHAPTER IV.

Phenomena that follow the Formation of the Follicle
and the Rupture of the Epithelial Cord, - - 115

8 CONTENTS.

CHAPTER V.

PAGE

The Place and Mode of Origin of the Follicles of the
Permanent Teeth, 127

CHAPTER VI.

Chronology of the Dental Follicle, or the Periods in
which its several Component Parts appear, - 147

CHAPTER VII.

Criticism of Theories, Resum6, etc., - - 169

Conclusions, ------ 181

Summary of Illustrations and Brief Descrip-
tive Review, - - - - - 185

TRANSLATOR'S [NTROblJCTION.

[Teacheb and ins IYiti.s. Caspbb ami Frank.]

r I TEACHER: I propose to consider the Ori-
-L gin and Formation of the Dental Follicle
in Mammals; and for this purpose I shall read
the valuable memoir of Drs. Legros and Mao-itot,
which furnishes the most complete account of
these phenomena of any work within my knowl-
edge. I shall use this treatise as a text, elabo-
rating as .we proceed, whenever suggestions may
occur to me, or in response to questions from
you. In this manner we may hope to arrive at
a satisfactory understanding of the subject.

§ I. -MUCOUS MK.MBKANE. '

^ on are presumed by these authors to be
acquainted with the general anatomy ami physi-
ology of the parts from which the teeth are

10 translator's introduction.

directly derived. Indeed, without this knowl-
edge you cannot obtain a very clear idea of the
origin and evolution of the tooth-germs, even
from the minute description given in these
pages. I think it will be well, therefore, before
commencing our readings, to hastily reviewT the
parts immediately concerned in the production
of the teeth, and especially the epidermis or
epithelium, which constitutes the external layer
of the mucous membrane.

Casper : I ought to have a pretty fair knowl-
edge of these parts ; if not, it is no fault of
mine, for I have faithfully studied Biesiadecki,
Kolliker and Klein ; and yet I must confess that
my knowledge is badly confused, especially in
regard to the mucous membrane; for these
authors do not represent this tissue by descrip-
tive figures, as they do the skin. Besides, the
names given to the different strata are a good
deal mixed ; so that I think a review of the
subject will not be a waste of time.

Teacher: The difficulties you have encoun-
tered do not surprise me ; for I have myself had
considerable trouble in determining even the
location of the layer which some authors have
described under that name. For example :

MUCOUS WEMBBANE. 11

I I i A.ecording to Borne authors, the epidermis
alone constitutes the mncous membrane (Guillol

and others).*

(2) According to others, the mucous mem-
brane consists of three membranes, viz., "an epi-
thelium, a proper mucous, and a fibrous coat."
"The second coat, the proper mucous membrane,
is apparently without texture. The third coat
corresponds to the corium of the skin.''

This is Prof. Hand's definition of the mucous
membrane, and essentially that of Prof. Leidy.
Here we have the term mucous membrane used
both in a general and a special sense, as a whole
and as an integral part; the mucous membrane
consisting of three layer*, one of which is the
proper mucous membrane, and the latter seem.-.
from its description, to be identical with the
''basement membrane" of Todd and Bowman,

*Prof. Wedl, in his "Pathologie der Z&hne" (Leipzig,
1870), under the heading of Development of the Teeth,
designates the mucous membrane as an epithelial structure,
and calls the enamel-organ a follicle of mucous cells:
"Dieser Schleimzellenschlauch wurde von Ko'lliker als
Schmelzkeim bezeichnet." This phraseology, to one who
had studied Frey, Magitot, Kolliker, Flint, Klein, and
many other physiologists who have described the mucous
membrane, would render Wedl's description unintelligible.

12 translator's introduction.

the "intermediate membrane" of Henle, and the
"membrana propria" of Kolliker and others.

(3) According to others, again, the layer situ-
ated immediately heneath the stratum Jfalpighii
(and which corresponds with the corium or
dermis of the skin) is "the proper mucous
membrane" (Kolliker, Klein, Flint, Frey and
others). These authors, however, designate the
lower portion of .the epidermis of the skin by
an equivalent term, mucous layer j but occasion-
ally they use the expression mucous membrane
in its general sense.

(4) Again, Dunglison and many other au-
thors employ the term mucous membrane in«
its broader sense, as including the "epidermis"
and the subjacent layers.*

You see, therefore, that the study of this
membrane is rendered unnecessarily difficult by
the numerous and often contradictory terms
which different writers use in describing it.

* Dunglison says: "In the mucous membrane the same
superposition of strata is generally considered to exist as
in the skin, viz., epidermis or epithelium, rete mucosum,
corpus papillare, and cutis vera."

M. Flourens divides all the mucous membranes into
three layers — the derma, epidermis and corpus mucosum.

Ml COUS MEMBRANE.

13

Kolliker and those of his Bchool divide the
mucous membrane (as a whole) into the follow-
ing layers, counting from the external:

ill Ejntheli/um; (2) mevthnmii mucosa (the
proper mucous membrane); (3) submucosa (sub-
mucous membrane i, tela rmtcosa, etc.

Fig. 1.

1st Class. 2d Class. 3d Class. 4th Class.

=

| Strat. corn.

s

-

a

- Strat. Malp.

If. memb.

o

■

Basement niemb.

M. memb.

t- . \ Par* pap.
Dermis- _

( Par- ret.

M. memb.

3

CD
=

Snbdermls.

-

Fig. 1. — The above diagram shows the relative position
of the different layers which are designated the mucous, or
"'proper" mucous membrane by various writers. The
column on the left gives the names, and location of the
strata of the mucous membrane as we think they should
be designated. The horizontal lines show the relative loca-
tion of these layers, without any regard to their thickness.

Some of these authors call the external por-
tion of the "membrana mucosa" the chorion,
corinm or derma. .They also divide the "proper
mucous membrane'9 into two layers, the pajril-
hinj and the reticulary.

Huxley says the skin and mucous mem-

■14

brane "may be distinguished into three por-
tions; a central plane of indifferent tissue [the
basement membrane], from which, growth and
metamorphosis take place externally, to consti-
tute the representative of epidermis or epithe-
lium, to which we propose to give the name of
ecderon / while internally, growth and meta-
morphosis take place from the central plane, so
as to constitute the representative of the derm
or 'mucosa,' which we have termed the en-
deron."*

ISTow, since the terms emploj^ed by different
writers to designate the layers of the skin and
of the mucous membrane are so various, and
sometimes conflicting, I shall apply the same
terms to the corresponding strata in both of
them, as follows :

(1) The term epidermis will comprehend the
whole of the external epithelial layer, whether
it be of the skin or of the mucous membranes.
(2) The term dermis will be applied to the
stratum immediately subjacent to the epidermis,
and which is known by the various terms, cu-
tis vera, corium, mucosa, proper mucous mem-

*Appendix to the Sydenham edition (4th edition) of
Kolliker's Histology.

MUCOUS MEMBRANE. 15

brane, etc. These two layers will be subdi-
vided,— the epidermis into two strata — the
corneous and Malpighian ;* the dermis also
into two parts, the papillary and retioulary.

The tissues next subjacent to the dermis
will he known as the subdermis, corresponding

to the subcutanea, subniucosa, tela mucosa, etc.

In thus applying these terms I make no new
departure in our nomenclature, but merely cm-
ploy the old ones more systematically, and, I
think, more rationally.

It must be confusing to the student to find
the lower layer of the epidermis of the skin,
and the layer that lies beneath the epidermis of

*The Malpighian layer, as defined by most authors,
includes those epithelial cells (of the epidermis) that lie
subjacent to the horny layer, whether their form be colum-
nar, polygonal or otherwise; but some authorities, among
whom are Legros. Magitot, Tomes and Ki'iss. limit the
term stratum Malpighii to the lowest layer of cells, which
stand vertically, like palisades, upon the surface of the
dermis. This single layer of columnar, or cylindrical cells,
as they are sometimes called, is also termed the prismatic
layer by Legros and Magitot, — a term which is. to-my mind,
definite and not liable to mislead the student ; and hence
will be employed in the following translation wherever it
occurs in the original.

16 translator's introduction.

the mucous membrane, — parts which are locally,
anatomically, and functionally, different, — both
designated by the same name; and not to find
a dermis beneath the epidermis. The term der-
mis cannot be objected to, as applied to a layer
of the mucous m.embrane, since the growths
originating in this stratum are universally de-
nominated dermhl tissues.

For the reasons here stated, I believe I am
justified in adopting the simple S}7stem of ter-
minology indicated above.

With this designation of terms, we will pro-
ceed with our description of the mucous mem-
brane, and more especially the exterior layer —
the epidermis, from which the tooth-germs
directly originate.

The mucous membrane and the shin are an-
atomically analogous and continuous structures.
The first clothes the internal, and the other the
external, surfaces ; and the description of the
one will, with slight modifications, apply to the
other. In a general sense, they are composed
of two strata or layers, the dermis and the epi-
dermis} yet for convenience of description,
rather than for any other reason, they have
been variously subdivided.

.Ml < OUfl MEMBRANE. 17

The externa] stratum, the epidermis, com-
posed entirely of epithelial cells, lias be(Sn de-
Bcribed as consisting of two layers — the exter-
nal being termed the corneous and the internal
the MaVpighian. The "scarf-skin" raised on the
external surface of the skin by a blister, and
the pellicle detached from the palate by hot
drinks, represent the corneous layer of the epi-
dermis ; by some authors this is called the
"true epidermis," and by some the "cuticle.'1
This layer is composed of the old epithelial
cells which have ceased to perform any of the
vital functions. The subjacent layer, formed of
living epithelial cells, which vary in form and
size, is denominated (among- many other terms)
the stratum Maljrighii.

Underneath these two subdivisions of the epi-
dermis of the mucous membrane (according to
the nomenclature here adopted) we shall find
the dermis {derm or derma). .But lest I should
mislead you I will mention here that there is a
transparent amorphous pellicle which separates
the lower stratum of the epidermal cells from
this latter layer. This structureless tissue is
described by Todd and Bowman under the name
of basement membrane, and by Eenle under that

18 teanslatoe's introduction.

of intermediate membrane. Now, although the
existence of a "membrane" here is disputed by
many, yet there can be no doubt that a homo-
geneous structure is interposed between these
layers, and that in some parts it presents the
character of a membrane of considerable thick-
ness. This membrane is of peculiar interest to
the dental physiologist, since the dentine-bulb
and the enamel-organ will be found on the
opposite sides of it. In this situation it consti-
tutes the membrana jprmformativa of Raschkow.
This tissue is not usually reckoned among the
layers of the skin and mucous membrane; and
its further discussion here, as a preformative
membrane, would be but to anticipate what will
follow in the body of this work.

Inasmuch as the elements of the epidermal
membrane (the epithelium) play the most im-
portant part in the development of the teeth,
as will be seen, hereafter, a more minute de-
scription will be given of them than of those
of the subjacent stratum.

These elements are derived from the exter-
nal germinal layer — the corneous leaf or plate,
(Remak), or the epiblast, as it is now more gen-
erally called. They are developed at an earlier

MUCOUS MEMBRANE. 19

period in embryonal life than are the connect-
ive-tissue cells of the middle or intermediate
layer — the mesoblast, from which the dermis
originates.

As early as the 35th day (as nearly as I am
able to ascertain) the epidermis presents- two
layers of cells ; but at this period it cannot be
regarded as a membrane composed of two 1am-
in;v, for the external cells haye not yet attained
the requisite age to mature them into the horny
bodies that constitute the corneous layer. The
cells constituting the epidermis must, therefore,
though differing in form, be regarded, at this
stage, as belonging exclusively to the Malpigh-
ian stratum (in its broader sense). But soon the
transforming hand of time will convert them
into the corneous layer ; when the oral epider-
mis will be, like that of the skin, divisible into
two laminae.* If we examine these two epi-

* In his last edition (5th), under the head of "Epithe-
lium of the cavity of the mouth,'" Kolliker remarks that
"the elements that constitute this epithelium [epidermis]
are not divisible, like the epidermis [of the skin], into two
clearly distinct lamina?, but constitute one connected layer,
more resembling the mucous layer, but representing also
^the corneous layer."

It may In' true that in some portions this epidermis

20 translator's introduction.

dermal strata of the mucous membrane more
closely, we shall find them composed of quite
regular layers of epithelial cells, which (com-
mencing with the lowest) may be described as
the infant cells, the youthful cells, the adult
cells, the aged cells, and the dead cells.

The cells composing the stratum corneum
belonged in their infancy to the lowest layer
of the stratum Malpighii ; in
their youth to a more external
layer known as the " prickle,"
"spinous," "ridged," "acu-
leated," or "imbricated" cells

(all of which terms are applied

,, , . _. Fig. 2. — "Spinous,"

to cells represented m Fig. «ridged,"or"imbri-

2). In their middle life they cated" cells. (From
belonged to the polygonal r
cells ("pavement, or tessellated epithelium"),
which lie still nearer the surface ; and in their
old age, to the elongated, flattened cells, in which
the nuclei have nearly disappeared : and finally,

is not so readily divisible as that of the skin ; but it is
known with what facility a pellicle may be raised from
the palatal portion — the rugae for example — by drinks
that are not sufficiently hot to produce the same effect
upon the skin.

MUCOUS MEMBRANE. 21

as dead cells, they occupy the most outward, the

corneous layer of the epidermis.

The cells of the lowest layer (the infant cells)
stand vertically, like palisades, upon the base
merit membrane (c); which latter separates the
epidermal from the dermal
Btratum of the mucous mem-
brane; or in other words,
the basement membrane
separates the epithelium from

the " mucosa," " proper mi.- FlG-3-~«. cylinder,

columnar or prismatic
cous membrane," or " cori- cells of the mucous

urn." These cells, which membrade, or "infant

cells"; fr, intermediate

may lie likened to the blocks matterj c, basement

of a Nicholson pavement membrane; d, fibrous

, , . . . . tissue of the dermis.

when set in position, consti- {FromFrejfm Diagram-

tute what is called variously matic.)
the prismatic, columnar, cylindrical, and, per-
haps less properly, the Malpighian layer. They
have large oval nuclei, and are said to be desti-
tute of a cell-wall. In the embryo (according to
Ilenle) they appear like a stratum of protoplasm
regularly studded with nuclei. This layer of
prismatic cells offers additional interest to the
dental student, since it constitutes the peripheral
portion of the enamel-organ, including that spe-

22 TRANSLATORS INTRODUCTION.

cial area which, during the course of develop-
ment, will be known as the "enamel-membrane"
(" internal epithelium of the enamel-organ " of
Kolliker, or "membrana adamantina''' of Rasch-
kow), and which here either is converted into
enamel or produces it. But more of this anon.
The next layer or layers of cells (the youthful)
have grown larger, and, besides their imbricated
appearance, are surrounded by a thin cell-wall,
periplast (Huxley), or formed material (Beale).
The cells external to these assume larger propor-
tions and are more polygonal in form, and repre-
sent these cells in their middle life. The cell-
wall, or periplast, has increased in thickness, while
the nucleus has proportionally diminished in size.

Fig. 4. Fig. 4. — This cut was

designed to illustrate the
cells of the epidermis. E,
in some of their various
phases, as described above.
E-{ yjpSg1 zL^_^^ jig a, Stratum corneum; b,

stratum Malpighii, with
its prismatic or columnar
layer resting upon the
basement membrane b m;
c, the upper portion of
the dermis. The papillse
are not represented in this
figure, nor is the subdermal layer.

MT« 0U8 MKMI'.KANK.

The cells still external to these are I

aid the nearer they approach the corneous
stratnni the larger will be ' the amount of
"formed material" that surrounds the nucleus;
till at last only a trace of the latter is visible,
or it entirely disappears, and these cells enter
the horny layer and become the Us —

a lifeless protecting covering for the living ce-
ments that are growing up beneath.

Thus these cells, during their passage from
the interned to t?t<: external surface, have un-
dergone all these changes, until from prismatic
or columnar cells they have finally become thin,
98 scaleSi which are continually cast off" as
foreign or etfete matter. During the entire life
oi' a person these cells are continually passing
away ; and hence the production oi new genera-
tions of them must be equally incessant. This
reproduction takes place from the lower
oi vertical cells, i. «., the cells that constitute
the prismatic or columnar layer: at least this
is now the most generally accepted opinion of
physiologists, though with some respectable ex-
ceptions.

The external layer (stratum oom&um) of the
mucous membrane, unlike that of the skin, is

24 translator's introduction.

permeable by various kinds of liquids; which,
after passing through the softer portions of the
epidermis and the basement membrane, may be
absorbed by the vessels of the dermis (proper
mucous membrane, corium).*

tTow, lest your patience be too heavily taxed,
we will take only a very hasty glance at the sub-
jacent layer of the mucous membrane, ignoring,
for the time being, the existence of the basement
membrane.

Lying immediately beneath the epidermis we
find a fibro-vascular membrane of variable thick-
ness, which we call the dermis (the proper
mucous membrane, the mucosa, mucous layer,

* Kolliker (Loc. Cit., 5th ed.j says: " The epithelium of
the mouth, though thick, is very pervious, a characteristic
which distinguishes it from the epidermis [of the skin], of
which the mucous layer [stratum Malpighii] alone possesses
this quality. It allows the various kinds of liquids to pass
through it from without inward, which, when brought in
contact with the mucous membrane [the dermis], may be
absorbed by the vessels, or become cognizant to the nerves
received by this membrane."

Kolliker does not recognize the existence of nerves in
any part of the epidermis. If the experiments of Langer-
ghans and Podcopaew are reliable, the liquids need only
enter the Malpighian layer to be brought in contact with
the nerve filaments that penetrate this soft layer.

Ml PODS MEMBRANE. L<;,

cutis vera, corinm, chorion, etc.) Thia is con-
tinuoua with the dermis of the skin, and gradu-
ally merges into the subdermal areolar tissue,
with whirl, it is strongly and intimately con'
nected. The externa] portion of the dermis
known as the pars papillaris (papillary part),
;""1 the subjacent portion as thenars reticularis
reticulary or netted part). But we cannot dwell
upon these particulars, which do not, in fact, exist
in the dermis at the early period of embryonal
life when the development of the teeth com-
mences. J will .ay, however, that the promi-
nent constituents of the dermis are the connective
tissue elements; hut, as before stated, the cells
of the mesoblast, to which this layer belongs, are
no! developed at so early a period as those of
the epibUst, from which the epidermis is derived.
For example, till the forty-fifth day of gestation^
••""1 perhaps later, the 'dermis is represented by
a nucleated mass of embryonal tissue, in progress
of evolution, while at the same stage the epi-
dermal cells are completely developed.

From tfu external surface of t7u dermis rises
the dentine^ulb, or dentinal papilla; though
many authors Mate that the papilla originates in

the "submucous" tissue. This latter tissue or

26 translator's introduction.

membrane corresponds with what I have termed
the subdermal tissue. But to me it is evident
that the dentinal papilla first appears as a little-
nodule upon the surface of the layer subjacent '
to the basement membrane — the dermis.

Fig. 5.

Fig. 5.— This cut
is taken from Bolli-
ker's Man'l of Hist.
It has been widely
copied by histologi-
cal writers, and rep-
resents "a simple
papilla [of the mu-
cous membrane],
with manifold ves-
sels and epithelium,
from the gums of
an infant, magnified
250 diam." It is
given here princi-
pally to show the
epidermal covering,,
though the cells are
represented only approximately correct, the figure being de-
signed mainly to illustrate the vessels of the papilla. It will
be observed that the "ridged" cells do not appear m this.

With this imperfect description, which has
been confined mostly to the situation of the lay-
ers, and to some of the more conspicuous elements
of the mucous membrane, I must drop this fasci-
nating subject ; hoping, however, that what has

I'l \ BLOPMBNT OF THE 3 a \\ 8,

a i

been said will repay the time it has occupied,
and more especially thai the little information
you have thus gained will stimulate you to seek
a more thorough knowledge of thi.s very impor-
tant, and very extensive, branch of histology and
physiology.

§ tt.— THE EARL1 DEVELOPMENT OF THE JAWS;
AND MECKEL'S CARTILAGE^

As Meckel's cartilage is alluded to in the first
pages of the following treatise, perhaps 1 had
better anticipate your questions in regard to it;
for a description, that would be at all satisfactory,
would make too long a break in the text.

1' bane : I have seen this cartilage mentioned
in various works, but never described; and I am
curious to learn something of this, to me, myste-
rious organ.

Ceaohee: Since our medical and dental liter-
ature is so reticent in regard to this important
embryonal structure, and the authors of this
work scarcely more than allude to it. I will give
you a very brief historical account of it. The
facts that 1 Bhall give you regarding it have been
gathered mainly from a treatise written b\ Drs.
M.'igitot and Rubin (the first named being one

28 translator's introduction. .

of the authors of the present work), in which this
subject is very fully elaborated, and from which
most of the illustrations here given are copied.

I will commence at a period some ten days
anterior to the origin of the cartilage, and briefly
sketch the progressive development of the
jaws till it makes it appearance ; and then trace
their phenomena together to the time when it
disappears.

If we examine a human embryo of fifteen to
eighteen da}rs (total length, little over half an
inch), we shall find two tubercles which proceed
from the first visceral arch, and which, when de-
veloped, will constitute the lower jaw. These
tubercles, processes, tongues, apophyses or bour-
geons (take your choice of these terms) gradually
approach each other until they unite at the me-
dian line, and, at a later period, become ossified.

This union takes place about the twenty-eighth
day, at which period the embryo has attained
perhaps three-fourths of an inch in length. But
coincidently with the growth of these two pro-
cesses, two other bourgeons, or buds, shoot out
from the same " visceral arch " to form the supe-
rior maxilla. (Fig. 6, 5, 5). (Fig. 7, g, g).
• The growth of these is also toward each

DEVELOPMENT OF THE JAWS

29

otlu-r; bat, unlike the former two, they never
UUiU' with each other aor meet at the median
line: for there is still a third pair of bourgeons,
called the incisive or intermaxillary, which
arise from the forehead or frontal apophysis;
and these, in their downward growth, occupy
the central portion of the open space between
the maxillary processes. This will be seen by
a -lance at Fig. 6, 4, and Fig. 7, II, although

Kig. G.

L^

Fig. 6.— Mouth of an
embryo of forty days.
(Coste.) 1, First appear-
ance of the nose. 2. 2,
First appearance of the
abe of the nose. 3, Ap-
pearance of the closure be-
neath the nose. 4, Middle
or median portion of the
upper lip forme,/ lnj the
approach and union of the
two incisive proa ust s ■
the little notch in the
median line still indicat-
ing the primitive separa-
tion of the two processes.
5, •"). Superior maxillary
processes forming the
lateral portion of the up-
per lip. 6, 6, Groove for
tli'' development of the

lachrymal sacs. 7, Lower lip. 8, Mouth. 9, 9, Lateral halves

of the palatini arch, already nearly approximate! in front
but still widely separated behind.

30

TRANSLATORS INTRODUCTION.

they have, in these cuts, already united with each
other at the median line. These last-named pro-
cesses, when ossified, will constitute the inter-
maxillary bones. A line, faintly representing
the point of union of these two processes, may
be seen in Fig. 7, but is not portrayed in the

Fig. 7.

Fig. 7. — A vertical section of the anterior part of the
face of a human embryo of forty to forty-five days. Magni-
fied 80 diameters. (Magitot.) a, a, Meckel's cartilage;
F, F, F, F, the mouth; g, g, superior maxilla?; H, H,
incisive, or intermaxillary processes; the perpendicular
line showing their point of union with each other.

DEVELOPMENT OF THE JAW8. 3]

original plate. It is added here to avoid givine
yon the impressioD that this iQ&aingle process.
There is a slight notch or clefi still remaining at
the lower margin, between the intermaxillary
processes (Fig. 63 4), which in a subject a few
• lavs older would have been closed.

Soon after the intermaxillary processes have
become united with each other (say in rive to
eight days), their free lateral margins form a junc-
ture, and coalesce with the advancing superior
maxillary processes, thus closing the vertical clefts
seen in Fig. 7 (above the letters F), with the ex-
ception of two small apertures for the nostrils.
(Fig. 6, 2, 2.) All these processes are outgrowths
from the mesoblastic layer, clothed externally
with a coat of epithelium from the epiblastic.

From this brief sketch of the mode of devel-
opment of the maxillary and intermaxillary pro-
cesses you- will readily comprehend the origin
of that common malformation known as hare-
lip. When from any cause one of the maxillary
bourgeons fails to unite with the intermaxillary
process, we have "simple hare-lip"; a similar
failure on both sides results in "double hare-lip."
If. in addition to these lateral fissures, one occurs
at the median line (which is not frequent), we

32 translator's INTRODUCTION".

have "complicated hare-lip." Occasionally there
is the central fissure alone, in which case the
intermaxillary processes have failed to coalesce
with each other — a rare occurrence.

"We Avill now return to the lower jaw. As
before stated, the processes (sometimes called the
mandibular), from which this maxilla is devel-
oped, meet, from about the twenty-fifth to the
twenty-eighth day, and form a union with each
other at the median line. (Fig. 6, 7.) Very soon
afterward a little cartilaginous band makes its-
appearance (" by direct genesis "), and occupies
the central portion of the embryonal mass that
now represents the lower jaw. This is

Meckel's cartilage

in its incipient stage of development. It is a
small whitish cord, lying in a bed of soft trans-
parent tissue, and may be easily distinguished by
the aid of a low magnifying power; and by care-
ful manipulation it may be removed entire from
the surrounding mass for examination. This car-
tilage was first noticed and described (in 1820, I
think,) by the celebrated German anatomist whose-
name it bears. It gives form and stability to the
lower jaw of the embryo, serving as a temporary

MECKEL - I AIM ll \(.l..

33

skeleton, from an early period till it is no longer

iifi'tlcd i'(.r that purpose. It is composed of two
symmetrica] or homologous parte (corresponding
to the right and left sides of the jaw), which
soon become united at the ?//< nf<il symphysis.
From this point <>t' juncture they extend, one <>n
either side, to the frame of the tympanum, where
they terminate in the malleus. | Pig. s. b.)

Fig. 8. Fig. 8.— Cranium

of a human foetus of
four months, natural
size. Dissected for
the purpose of show-
ing the membrane
of the tympanum at
this age, with the
cartilages of the in-
cus and of the mal-
leus (b); also, the
extra-tympanic por-
tion of Meckel's car-
tilage [a i. [Magitot
(nid Rubin).

This cartilage is said to constitute the first
solid structure that appears in this visceral arch ;
and from its commencement (about the twenty-
fifth day), until it entirely disappears,* it under-
goes a constant series of modifications.

* Although Meckel. Valentin, and sonic others, extend
the existence of this cartilage to the eighth month in the

34 translator's introduction.

It has scarcely attained its full growth (which
period corresponds to the commencement of the
ossification of the malleus),* when it begins to
waste away and disappear.

Between the thirty-fifth and the fortieth days
of embryonal life, slight traces of ossification show
themselves at points nearly equidistant between
the symphysis and the angle of the future jaw.
This extends rapidly, both anteriorly and pos-
teriorly, along the external face of Meckel's carti-
lage, in immediate contact but not uniting with
it ; and at about the sixtieth day of gestation a
miniature jaw-bone is formed, though not yet
perfected. (See figure below.)

» Pig. 9. Yig. 9. — Taken from a human embryo of

^JSSgZ^g about sixty days. Natural size. Soft parts
" removed, showing Meckel's cartilage and the

inner, or lingual face of the jaw-bone, left side. The cartilage
has much the appearance of a very large hog-bristle. The
main object in presenting this figure is to show the stage of
development at this early period, i, Symphysis; a, extra-
tympanic portion of Meckel's cartilage; n, manubrium mal-
lei. (Original figure.)

human foetus, yet Drs. Magitot and Eobin state that they
have never been able to find a trace of it later than the sixth
month. As for myself, I have never succeeded in finding the
slightest vestige of it, even at the symphysis, at the end of
the fifth month.

* The latter part of the third month of embryonal life.

MKCkhl. S ('AIM II. \i;| ..

35

At tin's epoch the skeleton of the lower jaw
is composed of tw<> arches (if we may include
Meckel's cartilage in the term skeleton), — an
arch within an arch, an internal cartilaginous
and an external osseous one. (Figs. 9 and l"
represent one of its bi-sections.)

Fl«- 10- I i... 10. - Internal

face of the right in-
ferior maxilla of a hu-
man embryo of about
three months, showing
the natural size and
the relative position of
Meckel's cartilage : as
also the dental follicles,
from which the internal face of the bone is lifted off:
a. the extra-tympanic portion, often flexible beyond the ori-
fice of the dental canal; h. the symphysis of the cartilage;
n, the manubrium mallei (or handle of the hammer), with
a little fibrous prolongation ; c, the cartilage of the incus
(or anvil). This figure represents the internal surface of
Meckel's cartilage, or the interior of the arch. (Magitot and
Robin).

In an anatomical view this cartilage consists
of two parts — a transitory maxillary, or ex-
tra-tympanic, and a persistent auricular part.
The former, after it is no longer needed to bus- ■
tain the jaw, begins to waste away : while the
latter, which represents the malleus, gradually
becomes ossified.

36

TRANSLATOR 8 INTRODUCTION.

Fig. 11.

Fig. 11. — Meck-
el's cartilage, from
a human embryo of
forty to forty-two
days, and before the
appearance of the
maxillary bone;
magnified twenty-
five diameters. af
Enlargement of the.
cartilage near its
union with the neck
of the malleus ; br
a slightly enlarged
portion of the car-
tilage in the form of
a spatula, but con-
tracted at the me-
dian line, where it
unites with that of
the opposite side ;
m, head of the mal-
leus ; n, handle of
the malleus; e, car-
tilage of the incus;
o, cartilage of the
os lenticulare ; I,
cartilage of the
stapes. [The outline
of a jaw has been
added to this figure
to show the relative
position it will oc-
cupy when ossifica-
tion takes place.]
(Magitot and Robin. )■

\n:< kel's cartilage. 37

This (tssiiicitinii ut" the auricular, and absorp-
tion of the transitory, portions commence al the
end of the third month of intra-uterine life; the
former with the malleus, the latter at points
corresponding with the middle portion of each
jaw. whence atrophy extends in both directions;
and, toward the latter part of the sixth month.
according to these authors, the cartilage, from the
simphysis to the malleus, entirely disappears,
leaving for a time on the surface of the bone a
slight groove to mark the place it occupied.

Frank : I infer that Meckel's cartilage belongs
exclusively to the lower jaw of the human foetus.

Teacher: It is by no means the exclusive
heritage of man. All the different species of
mammals, reptiles, fishes, and even birds, in em-
bryonal life possess this transitory, cartilaginous
support to the lower jaw. But it does not in
all these disappear (as it does in main before
birth. In the rodents, — rats and mice, for ex-
ample,— it remains without sensible change till
birth, or a little later.

This brief description, aided by these excel-
lent cuts, will, I hope, give you a sufficiently
accurate idea of this cartilage to satisfy you for
the present. But if you desire further infor-

38 translator's introduction.

mation. I must refer you to the thoroughly
exhaustive treatise already alluded to ; * for I
know of no comparatively complete work upon
this subject in the English language.

§ III.— INTER-MAXILLARY BONES.

Casper : There is another obscure point that
I would like to have cleared up before it escapes
my mind. In your remarks you have referred
to the origin of the " mfer-maxillary bones." I
was not aware that any such exist in the human
skeleton. Our medical and dental text-books
say: "The maxillary bones are two in number,
united on the median line of the face." If
this be so, where can we locate the inter-
■ maxillae ?

Teacher : The reason why your text-books
do not describe these bones is, probably, because
the authors recognize their .existence only in
early foetal life, and hence do not deem it neces-
sary. But naturalists consider them very im-
portant features in zoological science, since the
point where they unite with the maxillae forms

* See Memoire sur un Organe Transitoire de la Vie Fcetale,
de"signe sous le nora de Cartilage de Meckel. (E. Magitot
et Ch. Robin. Paris, 1862.)

INTKKMAXILLAKY I '.ONES. 39

the dividing line between the incisor and canine
teeth. It seems to me that an intimate knowl-
edge of these parte is essential to a thorough
education in general medicine, and especially in
the department of dental surgery.

In foetal life the upper jaw is composed of
four bones, viz., two maxillary and two inter-
maxillary. In each of the latter will be devel-
oped and supported two incisors — a central
and a lateral; in each of the former, one cuspid
and all the teeth posterior to it.

Although the intermaxilhe are distinct bones
in the human fetus, their external surface is
soon covered over with a process from each max-
illa, which extends toward the median line, and
becomes intimately fused with the former before
birth; so that the intermaxillary suture cannot
be seen on the outer side ; but on the palatal
aspect of these bones the suture can always be
recognized at birth, and can often be traced
even in adult life. (Flowers, Linnaeus Martin.)

In many animals these remain permanently
as separate bones; and in human subjects, where
the jaw is malformed, detached pieces are often
found in this situation, probably owing to their
arrested development. (Gray.)

40

TRANSLATOR S INTRODUCTION.

By Huxley, and many other authors, these
bones are called the premaxillce • these parts
are also known as the incisive region, from the
fact that the incisor teeth are implanted in
these bones.*

Fig. 11.

Fig. 11. — From a foetus of
about four months; showing the
palatal aspect of the inter-max-
illary bones, and indicating the
points that will be occupied by
the teeth when developed; also
the inter-maxillary suture sep-
arating the canine and incisor
teeth.

* Perhaps it is due to the reader that I here state that
the existence of these bones in the human skeleton is not
an altogether uncontroverted question. I had prepared a
somewhat extended article, giving a sketch of the treat-
ment this subject has received from the pens of many
anatomists and naturalists, from the days of G-alen to the
present. But on reflection I have concluded to suppress
it, together with much other collateral matter, lest the
work should be so much cumbered thereby as to render
it tiresome or confusing to the student. The fact, however,
stands unshaken, (as stated by Prof. Paul Gervais, in his
work on the human skeleton, Paris, 1856,) that Vicq-
d'Azyr and Goethe have shown that these bones exist in
the human species, as well as im all the other mammalia.
The thought that Goethe, the great poet and naturalist,
has made these little bones the object of special scientific

DEFINITION OF TERMS. 41

§ IV.— DEFINITION OF THE TERMS FCETUS, EM
BRYO, FOLLICLE AM' BOURGEON.

Frank: I notice thai sometimes yon employ
the term embryo and sometimes fcetw. I sup-
pose they have the same meaning?

Teacher: Magitot, Kolliker, LegroB, Frey,
Gray, and many other reputable authors, use
these terms indiscriminately, as words of the
same signification. On the other hand, Dungli-
son, Palmer, Carpenter, Flint, and others, employ
the term embryo to designate the rudimental be-
in-- during the first four months of intrauterine
life, after which they style it the foetus. Some
again (including some of the last-named au-
thors) divide the period of gestation into three
stages. In the first the germ is called an ovum.;
when this begins to assume the appearance of

study may, in the minds of some, lend a charm to this
subject that it would not otherwise possess.

It cannot he doubted, I think, that these bones originate
from separate points of ossification; but they certainly, a*
a rule, become fused with the maxillary bones, on the
external surface, at a very early period of fietal life, some-
times before the fifth month; while on the palatal aspect
the suture is often distinct, extending across the external
alveolar process after birth.
4

42 translator's introduction.

a body, it is termed an embryo / and about the
end of the fourth month (the time corresponding
to the period of " quickening ") it is accorded
the name of foetus, which designation it retains
until birth.

This application of the two latter terms to
different periods of gestation is entirely arbi-
trary, and in some respects objectionable; but
I shall generally adopt it, since it possesses some
advantages. But sometimes it will be almost
unavoidable to speak of embryonal or foetal life,
as equivalent to intrauterine life.

Frank: While you are defining terms I
would like to know just what our authors mean
by "dental follicle."

Teacher : The dental follicle includes the
following parts: the dentine-bulb (papilla), the
enamel-organ, and the sac that envelops them
which is' called the follicular wall. These three
parts constitute the dental follicle.

The word follicle is not used here in its
primary signification — a little bag or sac — but
as a sac and its contents. Kolliker employs
an equivalent expression, dental sacculus, in the
same sense. This word follicle is also simi-
larly employed by many other anatomists, — as

DEFINITION <»F TERMS.

4-'i

"Graafian follicle," "Malpighian follicle," etc.
Tomes, and English and American writer.- gen-
erally, ose tin' terms follicle, Bac, and capsnle, as
words of the same meaning. It is unfortunate
that BOme definite and universal term is not em-
ployed to designate these associated parts of the
developing tooth ; but for want of such, I shall
retain the term follicle in the sense that it is
used by the authors of this work. (Fig. 12 very
well represents a dental follicle.)

Fig. 12. — This
cut is taken from
the fifth edition of
Kolliker's HistoVy.
Though the enamel
and dentine are al-
ready pretty well
developed, the mass
represented by the
figure is still a den-
tal follicle. It is
from a feline em-
bryo magnified
fourteen diameters.
a, Dentine-bulb; e,
enamel -organ ; //,
follicular wall.

44 translator's introduction.

Frank : Now, one question more. You used
the term " bourgeon " several times during your
description of the development of the jaws. It
is not a familiar word to me, though I suppose
it means about the same as process.

Teacher : The word means bud. germ, shoot,
or sprout; and the primitive outgrowths are
called bourgeons, apophyses, processes, etc. It
is a French word, but has become Anglicized,
and may be found in your English dictionary.
This term is often employed in the text as sig-
nifying enamel-germ, or enamel-bud. When the
buddings take place which develop into enamel-
organs, these offshoots or buds are denominated
bourgeons of the enamel-organ, or simply bour-
geons.

I cannot close these introductory remarks
without a word of apology for the term "cell,"
which has been used so freely in the foregoing
pages. Now although this, or its equivalent,
zellen, cellule, or cella, has been almost univer-
sally adopted by anatomists, the word, as applied
by them, is manifestly a misnomer. And yet its
primitive signification, as first used by Schleiden,
has been so modified from time to time, to cor-
respond with our clearer conception of the mor-

i»i;i IM i ion OF TERMS. 45

phology and nature of the little mass of matter
1 1 1 1 1 > designated, that it will require greal philo-
logical research to discover a substitute which
will be as definite and comprehensive as this
term, thus modified, has now become. Never-
theless, it is a stumbling-block to the student,
and is an example of the many defects in our
terminology, that a tew scientists, prominent
among whom I may name Dr. Atkinson, of
New- York, are making praiseworthy efforts to
remedy.

With a few preliminary remarks from our
authors, we shall now he introduced into our
main, and most interesting, field of study.

THE AUTHORS' INTRODUCTION.

TIIK work we publish to-day comprises the
first part of a series of studies, which em-
brace the entire phenomena of the evolution of
the dental system of mammals.

This subject, which, as you are aware, is
one of the most difficult that we have to en-
counter in embryology, and which is still in-
volved in very great obscurity, has been made
bv us the field of extensive investigations,
both on the human embryo and on those of
the domestic animals. By these studies we have
been convinced that the phenomena presented
in the series of raamraifera have (except in a
few minor differences) a perfect similarity in
their general physiological facts; the develop-
ment of the follicle, the anatomical composition
of its parr-, ami the role which these perform
in the functions of the dental organism, are in
all respects similar.

Our researches in this direction have been
stimulated not solely by the state of uncertainty
and of controversy in which this question is

48 THE AUTHOKS' INTRODUCTION.

involved, but also by the perusal of several im-
portant works published of late years in Ger-
many by different anatomists, — Kolliker, Wal-
deyer, Hertz, Kollmann and others.

The results presented by these observers have
gained, for certain parts of the question, consid-
erable importance. They have determined some
new elements that are a legitimate acquisition
to science; while other conclusions which tend
to invalidate certain doctrines advanced by sev-
eral English and French authors, lack, as we
shall endeavor to show, sufficient precision and
exactness. Besides, there are several questions
which remain without any solution whatever.

It is with the hope of throwing light upon
this problem, that we have undertaken this
series of researches.

Following rigorously the physiological order,
we have been led to consider successively :

1. The mode of origin and formation of the
dental follicle. 2. The morphology and struct-
ure of that follicle at the period of its complete
development. 3. The evolution of the tooth
within the follicle.

The present memoir will be devoted to the
consideration of the [two] first of these questions.

THE OliUJIX AND FOLIATION

DENTAL FOLLICLE

CHAPTER I.

THE CONDITION OF TIIK JAWS OP THE EMBBYO AT THE
PERIOD OF THE (JENESIS OK THE FOLLICLE. THE
EPITHELIAL RIDGE i BOVRRELET).

T

IIIOUGII we do not intend to dwell

-1- long upon the general constitution of
tlif jaws at the time of the genesis of the
follicle,"" still we think we ought to lay
special stress upon certain points which are
directly connected with our subject.

A- regards the lower jaw, it is known
that at a certain epoch in embryonal lite,
varying according to the species of animals,
the maxillan arch, absolutely destitute of

* See Memoir on the Genesis and Development of the
Dental Follicles, by Ch. Robin ami E. Magitot; in the physio-
logical journal of Brown-S6quard, 1800.

50 THE ORIGIN AND FORMATION

the least trace of osseous tissue, incloses
within its component elements a symmetri-
cal cartilaginous band ; and that this, unit-
ing with its fellow at the median line, or
the future symphysis, extends not only the
whole length of the maxillary arch, but
even to the frame of the tympanum.

This is Meckel? s Cartilage, — an organ
which plays only a transitory part in the
development of the maxilla, and occupies
the interior part of the arch. Thus embed-
ded within the embryonic tissue, it repre-
sents, at this epoch of intrauterine life, the
only fundamental elements of the jaw.
(Figs. 8, 9 and 10, pp. 33-4-5.)

As to the upper jaw, the period of evo-
lution corresponding with that which we
have just described in the lower, is that at
which the maxillary bourgeons have united
with the median or intermaxillary bour-
geon.* This phenomenon takes place in

* [These authors speak of the two maxillary bourgeons as
uniting with the median or intermaxillary bourgeon. From
this it would be inferred that there was but one intermaxil-

oi THE DENTAL FOLLICLE. 51

the human embryo about the fortieth or
forty-fifth day.

The two maxillary arches being thus
formed, we soon obsen e thai in the rounded
part (which will afterward constitute the
alveolar border), there is produced a bed
of epithelial cells forming a protuberance
or smooth ridge (saUlii ou bowrrelet), and
without any fold or depression whatever.
This ridge, visible to the naked eye, is still
more manifest in a section cut perpendicu-
lar with the axis of the maxillary arch, and
is composed of a thick bed of cells. It will
he noticed that on its sides an epithelial
coat is formed of only a few rows (rangees)
of these cells, superposed upon each other;
and sometimes, even of a single row.

The epithelial ridge is thus added to the
embryonal elements before fchej include any

lury bourgeon. They use the singular number here, prob-
ably because these bourgeons have already formed a union
at their external margins, which connection takes place a
little before their union with the maxillary bourgeons.— See
Robin ami Rfagitot, loc cit.. p. 9. — Tr.]

52 THE ORIGIN AND FORMATION

other well defined tissues, unless it "be some
vessels, nerves, and muscle-fibres, in process
of evolution.

This epithelial ridge has some peculiari-
ties which are of sufficient importance to
demand our special attention, and which
one would not suspect from simply examin-
ing its buccal or exterior surface. In a
vertical section you will notice the smooth
and rounded ridge that it presents in the
mouth, and which justifies the name we
give it — maxillary rampart (Kieferwall
of Kolliker, Waldeyer and Kollmann).

Fig. 13. Fig. 13. — From Thiersch's prepa-

ration of an embryonic pig (copied
from Frey). d, A mass of epithe-
lium — the ' ' dental ridge, " " max-
illary rampart " or " Kieferwall
(represented by the same letter in
the preceding and following cuts);
b, younger layer of epithelium; c,
the deepest layer — the prismatic or
columnar stratum; e, enamel-germ.

Beneath this external ridge a projection
sinks into the subjacent elements, the out-
lines of which represent nearly the form

e-^m

OF THE DENTAL FOLLK i.i . 53

of the letter I . wit 1 1 the apex slightly in-
clined toward the inner side | Fig. 14, d, <1 ).

PlO. II.

-il?t *••■»*:;","

Fig. 14. — A perpendicular section taken from the inci-
sive region of the lower jaw of an ovine embryo (lamb),
forty-two millim. in length (magnified eighty diameters.)
d, '/. Kpithelial band Q>ourrelet)\ <<, ". transverse section of
Meckel's cartilage near the symphysis: c, c, depression of
the mucous membrane; c, section of the tongue. (See same
letters Fig. 7, p. 30.)

Casper: I cannot see the appropriateness of

the term "epithelial ridge" which is used so
often. In tin1 plate it looks more like a groove
than a ridge.

Teacher: This term does not, to my mind,
express definitely the thick epithelial bed, which,
though it presents on the external surface of the

54 THE ORIGIN AND FORMATION

jaw an eminence or ridge, yet sinks into the
substance of the jaw to a greater depth than it
rises above the general surface. The word
used by the authors is bourrelet, which means
a rounded pad, or cushion. This structure was
for a long time supposed to be cartilaginous in
its nature, and hence called cartilago dentalis,
until Raschkow discovered its epithelial charac-
ter. M. Guillot (1859) named it the odontogenic
part, or the generating part of the teeth ; our
authors speak of it frequently as an epithelial
band, and we will hereafter so denominate it.

In a vertical transverse section this band is
represented, as has been stated, by the letter V,
with the apex bent a little inward. Now fill
this with epithelial cells, and heap them up,
and you have a tolerably accurate idea of the
epithelial bourrelet or band. In other words,
make a groove the entire
length of the jaw, shaped*
as just described, and fill it
" heaping full " of this cel-
lular mass, and it also will
represent the epithelial band,
as seen in fig. 15.

OF THE DENTAL FOLLICLE. f>5

Thus constituted, the hourrelei forms,
in reality, ;i continuous epithelial band,
Dearly vertical, the whole Length of the
alveolar border. It always exists in the
embryos of man and the higher mammalia,
and is even found on some parts which
will remain devoid of teeth, as in the bar
of the solipeds.

Frank: "The bar of the solipeds" is too
much for me; soliped, single foot. I did not
know there were any one-footed animals!

Caspki; : I know that the name soliped is
applied to the races of animals that have a single
hoof — as the horse and ass — but I am stuck
on the "bar."

Teacher: In animals, that interval between
the "tusks" and the molars, which is destitute
of teeth, is technically called the bar; and
though the band extends along this portion of
the jaw, it is unproductive, and becomes atro-
phied and absorbed, as we shall see further on.
The more elegant term Hiasti'ina is quite com-
monly employed to denote this vacant space be-
tween the teeth of the soliped, as well as those
that may occur in the jaws of other animals.

56 THE ORIGIN AND FORMATION

I will give you the substance of a very inter-
esting foot-note from the pen of Dr. Pietkiewicz
(a former pupil in the laboratory of Prof. Robin)
on the Rudimentary Dental Organs of the Rumi-
nants. It has been inserted here with the in-
dorsement of the authors of this work ; but
owing to its great length 1 shall give only a
brief summary of its contents, as published in
the "Transactions of the American Dental Asso-
ciation,".1878 :

You are aware that there is a wide-spread belief, which
had its origin in the announcement of Goodsir, in 1839,
that rudimentary incisor teeth may be found in the em-
bryonal jaws of Ruminants. This statement, founded upon
certain anatomical appearances, was seized upon by Darwin,
Hseckel, and other scientists, to sustain their views regard-
ing- the changes that had taken place in the successive
generations of animal beings; and thus the theory received
additional credit and a fresh impulse, until it has now
become the prevailing belief, that the upper jaws of the
fcetus of ruminants contain germs of teeth; which, however,
disappear before, or soon after, the birth of the animal.

This conclusion of Goodsir, which was never carefully
verified, has recently been severely shaken, if not entirely
overthrown, by the researches of Dr. Pietkiewicz.

He says, that in attempting to verify the statement of
Goodsir, which had obtained such extensive circulation
and credit, he made experiments upon a series of embryos
of cattle and sheep, taken in large numbers, from the

of l III DENTAL FOLLICLE. 57

earliest period of intrauterine life until they bad attained
thirty centimeters, or one foot, in length. In this series
of investigations, be ooi only never witnessed the presence
of a dental germ, but never found even a trace of the
epithelial lamina.

He further states, however, thai in the commencement
of his work he was led into an error by the deceptive ap-
pearance of the sections made entirely from the anterior
portion of the jaws; for in these he found on each side of
the median line an epithelial sac, which extended from
the mucous membrane into the depth of the jaw, and which
appeared to constitute the commencement of dental germ-.
such as Goodsir undoubtedly conceived them to be. No
difference was observed between the epithelium of this sac
and that of the mucous membrane, of which it appeared
to be a depression. The Malpighian layer constituted its
outer investment, while in its interior was found paviment-
ous epithelium.

From this appearance, he thought one could easily
conceive how Goodsir might have been led into the belief
that he had discovered dental germs. But in continuing
to make sections from these jaws in a posterior direction,
he found that the little sac assumed the form of a circular
canal, and approached the mucous membrane of the nasal
fossa-. Around this canal appeared a cartilaginous cornet,
and in the upper part was a mass containing vessels. From
this he recognized the organ of Jacobson. There was ab-
solutely nothing, he says, that could be, even remotely,
compared to the germs of the incisor or canine teeth.
5

58 THE ORIGIN AND FORMATION

The form of the epithelial Land is the
same in the different species of animals;
and while it presents its broadest aspect on
the alveolar ridge, it grows thinner, and at
the same time bends a little inward, as it
descends into the subjacent tissues ; so that
its internal or lingual face presents a con-
cavity, and its labial or buccal face a con-
vexity.

Though the deeper extremity, or apex, of
the band is blunt and rounded in the early
stage of development, it becomes very sharp
at the moment the first trace of the follicle
appears.

This band is composed of the same histo-
logical elements that constitute the epithe-
lial coat of the oral mucous membrane, —
that is to say, of nucleated cells, rendered
polyhedral in form by reciprocal pressure ;
and that portion which penetrates the tis-
sues of the jaw is bounded by a continuous
layer of prismatic cells. The cells that
compose the center of the band often

OF THB DENTAL loi.LiCLK.

(9

l'i... 15.

present .-it their borders thai denticulated
arrangemenl which has
been noticed by authors

in the cells of the epi-
dermis, and by which the
elements interlock with
each other. [Cells described in the Intro-
duction, as the "imbricated," " prickle," etc.,
to which list we will add here the explica-
tives "thorny" and "heckle." Fig. 15.]
fi... jB. As regards the prismatic

layer, it «lnes ii»i differ
^s from the stratum Mai-
d -■^^ /'/<////>, from which it is
directly derived. [Fig. 16, b. From F)'ey.~\
From the preceding considerations it is
seen that the epithelial band, which we
have jusl described, is simply a prolongation
of the epithelial tegumentary layer {couch. )
of the mouth, which, in sinking into the em-
bryonic tissues of the jaws, forms for itself,

SO to -peak, a groove which it exactly tills.

N<>\\. when the embryonal jaw is sub-

60 THE ORIGIN AND FORMATION

jected to a prolonged maceration, the band
may become spontaneously detached, thus
leaving an empty groove ; but at no epoch,
in embryonal life, can there be found, on
the surface of the alveolar border, any de-
pression, sinking, or perforation whatever,
when these parts are in a normal condition.
The well-known theory of the evolution
of the teeth advanced by Goodsir in 1837,
and afterward adopted by most authors,
was founded on a certain mechanism, which
consisted in the formation of the follicular
sac at the expense of an exterior depression
of the oral mucous membrane. The detach-
ment of the epithelial bed by maceration
may, doubtless, account for this tSror; but
nothing exists in the normal state of the
jaws to warrant any such conclusion. The
theory of Goodsir is, therefore, absolutely
without foundation in fact.*

* [For a long time Goodsir's theory of the evolution of
the teeth was held to be correct, and his verbal and pic-
torial representations were copied into our standard text-
books on anatomy and physiology, both medical and

OF THE DENTAL FOLLICLE. <>1

dental; and even Kdlliker, up to his fourth edition, bor-
rows from that author tin- cuts illustrating this stage of
.■volution, (ioodsir " believed that, at an early period of
total life, there appears a continuous open groove, run-
ning round the whole circumference of the jaws; that from
the bottom of this groove there arose isolated and un-
covered papillae, corresponding in number to the milk
teeth; that these papilla' become covered in by the deepen-
ing of the groove and the meeting of its two edges over
their tops, whilst at the same time transverse septa were
formed, so that the several papillae become enclosed in
their own separate follicles." — Tonus' Mux. of Doit. A nut.
" This theory of Goodsir was vigorously attacked at a
later date in works of the French histologists Guillot, and
Magitot and Robin. According to the latter, the tooth -
sacs, dental germs, and remaining parts are developed, in
the first instance, within the submucous connected tissue
(subdermis), quite independent of the epithelium or mu-
cosus." — F ni/. Tk.]

62 THE ORIGIN AND FORMATION

CHAPTER II.

THE EPITHELIAL LAMINA, AND THE GENESIS OF THE
ENAMEL-ORGAN.

"TTTE have seen that the part of the
• * epithelial bourrelet, or band, which
sinks into the tissue of the jaw, presents
two faces — an external convex and an in-
ternal concave one; and that it extends
the entire length of the alveolar border.
Now, as soon as the development of this
organ is completed, a thin process shoots
out from its internal face, which we shall
designate the epithelial lamina. (Figs. 17
and 18, E E.)

This lamina is a continuous process, ex-
tending the whole length of the epithelial
band, from which it emanates about mid-
way between its apex and the epithelial
layer (sometimes a little nearer the latter) r

OF THE DENTAL I OLLIOLE. 63

and appears t<> be a kind of diverticu-
lum (or inflexion) of the band itself.. It

Fio. 17.

Fig. 17. — A'ertical section of the anterior portion of the
lower jaw of an ovine embryo measuring 59 millimetres.
a. Showing the section of Meckel's Cartilage; d, epithelial
band (or bourrelet); c, fold in the mucous membrane; E,
epithelial lamina. These letters refer to the same parts in
the foregoing and following figures.

is somewhat flattened from above down-
ward, and it- rounded extremity is slightly
bent in the form of a crosier. ( Fig. 18, E. )
The elements of tin* lamina are of the
same character as those which compose the
band, viz., polygonal cells inclosed 1>\ a con-
tinuous layer of prismatic cells. As develop-
ment advances, Large polygonal cells make
their appearance in the thicker portion of

64 THE ORIGIN AND FORMATION

the lamina, similar to those found in the
band, or external epithelium. These ar-
rangements are important to be noticed ;
for, as will be seen hereafter, the prismatic

Fia. 18.

,===wi,=-sCL

■M

Fig. 18. — Transverse section of the left branch of the
lower jaw of an ovine embryo (65 millimetres in length),
magnified 260 diameters. This and the preceding cut show
the arrangement of the elements of the epithelial band, and
also the epithelial lamina.

d, Epithelium of the mucous membrane, extending nearly
vertically into the jaw and constituting the band and the
lamina. E, Epithelial lamina, emanating from the band.
The band and lamina are surrounded by the embryonal
tissue of the jaw. This portion of the engraving is faulty,
in that the nuclear elements are lighter than the surround-
ing mass, whereas they should appear darker,

(il THE DENTAL FOLLICLE. 65

elements which form its outer investment
arc never found in the debris of the Lamina,
nor in those of the epithelial cord which is
derived from it.

The t ilium l-nrijdu — the firsl trace of the
dental follicle — originates from points
upon the tree extremity of this lamina.
They show themselves, at first, as slight
tubercles arranged at intervals along the
margin of the lamina, and corresponding,
in number and situation, to the teeth that
will be developed in the firsl dentition.
To these protuberances we give the name
of primitive bowrgeon of the follicle (the
first follicular budding, or bud).

[In a foot-note these authors give their theory of the
origin of the supernumerary teeth; but, as Dr. Magitot (the
surviving author of this work) has since modified his views
in relation to this phenomenon, a mere statement of the
theory advanced by them will here be sufficient. Dra.
Legros and Magitot maintained that the supernumerary
teeth originate either from the epithelial lamina, from
supernumerary buddings arising between the normal num-
ber; or that they are off-ahoots from the epithelial cord.
In the Bra! case the development of these teeth would be
precisely Bimilar to that of the deciduous teeth; in the

6Q THE ORIGIN AND FORMATION

other, to that of the permanent teeth, with the exception
of the first molar.

The present views of Dr. Magitot upon this subject (as
recorded on pp. 36-7 of his treatise on the Anomalies of the
Teeth, 1877,) are in accord with those previously advanced
by Kollmann; and are based upon the well-known fact,,
that when the epithelial cord or neck, which connects the
enamel-organ with the epithelial lamina, becomes severed
by the closure of the follicle, the cells, of which the cord is
composed, multiply to a greater or less extent at their
severed extremities, — sometimes in great abundance. These
epithelial proliferations sometimes continue adherent to
the remains of the cord, and to the follicle itself, until they
are absorbed; and sometimes considerable masses become
detached, and, assuming various forms, wander into the
depths of the jaws (Fig. 19). These epithelial proliferations,,
according to Kollmann and Magitot, may become the-
enamel-germs from which the supernumerary teeth ori-
ginate.

Now, in order that a tooth may be produced, a super-
numerary dentine-papilla must be provided for this ad-
ventitious enamel-organ. This would result as a natural
consequence, if the theory advanced by the translator of
this work in a recent Report on Dental Physiology, before
the American Dental Association, is correct. (See Trans. r
1878, pp. 56-57). In this paper it was maintained that
dentine-papilke may originate from any point of the den-
tinal sheet of tissue (as described by Dursy), with which
the epithelial mass comes in contact; that it is solely
through the influence of the enamel-organ upon this tissue,
that the development of a dentine-papilla is induced. If

OF THE DENT \\. FOLLICLE.
Fig. 19.

<;:

'MB®'

- a Ma^s«^H

Fig. 19.— Taken from a bovine embryo, magnified 100
diametere. Tbia section is taken after the rupture of the
epithelial cord, and shows the epithelial proliferations that
occur in this region at this period of evolution. The cut
represents the territory between the wall of the follicle (o)
and the mucous membrane (<l).

//. Epithelial buddings From the follicular wall : /■:. /■:. bud-
dings and debris of the cord; F. globular masses from the
epithelial lamina.

68 THE ORIGIN AND FORMATION

this be true the origin of a supernumerary dentine-papilla
is readily accounted for; while otherwise, special papillae
must originate independently, and coincidently with the
supernumerary enamel-organ, — a circumstance that does
not come within the range of probabilities.

Thus, also, it seems to me. we find a rational and sat-
isfactory explanation of the origin of those families of
dwarfed teeth found in dentigerous cysts. — Tr.]

This bourgeon retains its connection with
the lamina, from which it is a direct deriva-
tion, by means of a slender cord or neck,
which gradually lengthens as the terminal
mass increases in dimensions.

During the whole course of*development
this bourgeon constitutes the enamel-organ;
while the neck, in its progressive lengthen-
ing, only serves as a temporary bond uniting
it to the lamina.

At its first appearance the primitive
bourgeon presents a nearly spherical form
(Fig. 20, E), and is comj^osed of an external
layer of prismatic cells (a continuation of
those of the lamina), inclosing a mass of
polygonal cells ; the latter being always

OF THE DENTAL I < LLICLE. 69

Less in diameter than those contained in
the lamina

Fig. 20.

FlG. '20.— A section of the epithelial lamina taken from
an embryonic lamb, a little older than that from which Fig.
18 was taken. (Magnified 350 diameters.)

c, I 'rismatic or columnar cells, — a continuation of the low-
est layer of the Malpighian stratum; tf, large polygonal cells
of the epithelial band (Jbourrelet); E, smaller cells of the
epithelial lamina. This lamina presents an enlarged ex-
tremity, and this enlargement represents the commencement
of the enamel -organ.

[The prismatic and the polygonal cells are beautifully
drawn in this figure.]

(§ee advancing stage of development, fig. 31.)

Let us here add thai during the progress
of evolution these elements (inclosed in
the prismatic investmenl ) undergo a modi-
fication whereby the} are transformed into
stellate bodi< a phenomenon thai never

70 THE ORIGIN AND FORMATION

occurs in the cells of the cord or of the
lamina. The disparity in the size of these
cells, together with the morphological
changes they experience, seems to us suffi-
cient to establish, from this period, a very

Fig. 21.

Fig. 21. — A section taken from the lower jaw of an
ovine embryo (left side), measuring 72 millimetres. (Mag-
nified 80 diameters.)

d, E, Same as in the preceding figures, g, Commence-
ment of the enamel-organ.

clear distinction between the constitution
of the lamina and that of the bourgeon
which emanates from it. We would em-
phasize this point, from the fact that the
more recent authors that have written upon
this subject have confounded these two
parts with each other.

OF THE DENTAL FOLLIOL] . 71

These differences, however, will be more
clearly manifest during the progress of evo-
lution, when we shall find the elements of
the bourgeon [enamel-organ] undergoing
a -cries of important changes; whereas
those of the lamina will invariably retain
their original appearance.

In continuing its evolution, the primitive
bourgeon, which was at first spherical, be-
comes somewhat cylindrical, though it -till
pursues a horizontal course until it has be-
come Qoticeably lengthened, when, by an
abrupt inflection, it takes a vertical direc-
tion, and sinks into the depth of the jaw.
Thus extending its course, the cord ac-
quires a length which varies according to
the species of animal, besides undergoing
certain secondary inflections. In man, as also
in the dog, the cord always remain- short,
and in the solipeds it is still shorter. In
the calf and in the land) — animals that
arc particularly favorable for these studies
— it describes divers undulations; bu1 we

72 THE ORIGIN AND FORMATION

have never observed in the primitive cord
that spiroid arrangement described by some
authors,* and for which, as we shall see,
the secondary cord (that of the permanent
teeth) is so remarkable.

These differences in the length of the
primitive cord are explained by the disposi-
tion of the special parts ; and determined, on
the one hand, by the species of animals, in
which the jaws have a greater or less ver-
tical height ; and on the other by the nature
of the future teeth. One readily sees how
the cord of the follicle of a permanent
tooth ought to be longer than that of the
temporary, since it must accommodate itself
to the longer passage it must make from
the place of its origin to its terminus be-
neath the follicle of the temporary tooth.

The primitive cord, in the course of its
progress, presents, moreover, some peculiar-
ities worthy of notice. These are the phe-
nomena of lateral buddings, which give rise

*See Kollmann, loc. cit., Taf. XIV, Fig. 2, v.

<)K THE DKNTAL FOLLICLE.

:;

to snmll rounded Qodules, in the form of
varicosil ies, \\ hicb, in t heir arrangement, re-
semble an irregular chaplet. (Fig- "-'-• ''•»
These lit t Le masses are composed exclusively

FlG. 22.

6>?

FlG. '22. — Taken from a section of the lower jaw of an
ovine embryo, measuring 82 millim, in length. (Mag
2G0 diameters.) c, Oral epithelium; /'. epithelial cord and
the •" varicosities" referred to in the text: </. enamel-organ;
//. dentine bulb; /, follicular wall rising from the base of
thelbulb; K, bourgeon from which the follicle of the per-
manent tootb will emanate.
6

74 THE ORIGIN AND FORMATION

of small polyhedral cells, analogous to those
contained in the cord itself.*

It is from these masses that, at a later
period, after the cord is ruptured, those
numerous epithelial prolongations spring,
which will be considered hereafter. It is
hardly necessary to say that we do not
here confound the buddings, just described,
with that special production from which the
cord of the secondary follicle originates, —
a point to which we will return further on..

After the cord has changed its course
from a horizontal to a vertical direction,
its extremity, which has already become
enlarged and club-shaped, acquires still
Greater dimensions. This results from the
multiplication of the polyhedral cells which
compose most of its mass, and from the

* [The cells referred to as being in the cord are not
shown in the figure. Only the prismatic layer, which
forms the outer coat, is represented here. The cord may
be compared to a tubular gland, the walls of which are
composed of a layer of prismatic cells (a continuation of the
stratum Malpighii), and the inclosed contents, of small
polygonal cells. Tr.J

<>F THE DENTAL FOLLICLE. 75

prismatic cells thai form the surrounding
layer, whose numbers increase in the same
proportion. This epithelial body thus
occupying the deeper tissue of the jaw
soon assumes a somewhat spherical. form ;
the superior pole corresponding with its
point of connection with the cord, while
the inferior pole points toward the bottom
of the jaw, inclining more or less toward
the lingual side. This mass represents the
enamel-organ as fully developed. Shortly
afterward the inferior pole becomes slightly
compressed toward the center of the enamel-
organ, which results in the formation of a
concavity in its lower or deeper extremity;
and the mass then assumes a shape re-
sembling a hood or cap, but still retaining
its connection with the cord.

This phenomenon of compression coin-
cides with the appearance of a new organ
in the jaws, th dentine-bulb [dentine-
papilla]. This, in fact, originates ;,t the
inferior pole of the enamel-organ, where

76 THE ORIGIN AID FORMATION

the compression takes place. It first ap-
pears as an opaque point, but it soon
assumes a conical form, and its summit
produces and occupies the corresponding
depression in the enamel-organ.

This reciprocal adaptation of the two
organs, which takes place from the first
appearance of the dental bulb, continues
throughout all their subsequent phases;
the enamel-organ always covering the bulb,
and exactly fitting its contours, whatever
may be its form, or the form, number and
disposition of the divisions it may present.
No connection of tissue, however, exists be-
tween the two organs at any stage of de-
velopment. Dissections of these parts, their
maceration in coagulating liquids, as well
as the examination of sections, all establish
this fact beyond question. This simple juxta-
position of the surfaces of these two organs
ceases, however, at the base of the bulb,
where the enamel-organ turns back upon
itself with a rounded border. (Fig. 22.)

OF THE DENTAL FOLLICLE. <7

It' we now examine the composition "I
ill,, enamel-organ, [al the period of develop-
in,. ni represented in Fig. 22, saj about the
fifteenth week of the human embryo, | we
find that the primitive elements (the polyg-
onal cells which occupy its centra] portion,
and ilif prismatic cortical Layer,) have under*
gone notable modifications. We discover,
in fact, that the middle region of this organ
is occupied by some elements of B,newform^
essentially differing in appearance from
that of the original cells. Thes< are stelldU
bodies, composed of a central nucleus, sur-

Fig. 28.

Fig. 28.— Stellate cells of the enamel-organ. (Dia-
grammatic, from Frey). Thesi cells are also very well
sliuwn in the preceding figure.

78 THE ORIGIN AND FORMATION

rounded by a transparent or finely granu-
lated mass, which ramifies and inosculates
with the neighboring elements. (Figs. 22-3.)

These star-shaped bodies occupy at first
only the center of the enamel-organ; those
near the periphery preserving their origi-
nal polygonal form, but becoming stellate in
proportion as the dimensions of the organ
increase. It will be noticed, however, that
the anastomosing processes are always much
longer and more ramified, as the cells are
situated nearer to the central portion ; while
in the vicinity of the periphery it is some-
what difficult to distinguish these processes,
as they are here only rudimentary. The
elements thus described are immersed in
a translucid amorphous mass, coagulable in
acids, and having the consistence and ap-
j^earance of the white of an egg.

These starred bodies — or " stellate cells,"
as they are usually termed, — are formed
directly at the expense of the polygonal
elements composing the internal mass of

OF III 1- DENTAL FOLLICLE. 79

the enamel-organ. The process is as fol-
lows: The substance mentioned above in-
terposes itself Little by little between these
originally small polyhedral cells, and thus
their walls lose their mutual contact, excepl
at certain points where they -till cohere.
A.s a dired resuli of this phenomenon, the
primitive polygonal cells exhibit a number
of depressions extending from their exterior
Burface toward the center, giving them their
stellate appearance.

From this transformation the primitive
cells would become entirely insulated by
the intervention of this new mucous forma-
tion, were it not for these connecting pro-
cesses, which give to this organ, a- a whole,
it- peculiar reticulated appearance, and t<>
each cell its stellate form. It is a remark-
able tact that no line of juncture can be
discovered where these cells are connected
with each other, the various re-agents failing
to disclose the leasl trace of it, so effectually
have these parts been cemented together.

80 THE ORIGIN" AND FORMATION

According to this theory, the stellate ar-
rangement of the "pulp" of the eaamel-organ
(the intimate composition of which we do
not purpose to describe in this memoir) re-
sults from a simple modification of the form
of the primitive polygonal cells, — a change
which they have undergone passively, as
it were. These elements of the enamel-
organ, notwithstanding their stellate form,
must be regarded, therefore, as absolutely
epithelial in their nature. The mechanism
of this transformation, however, differs ma-
terially from that given by Kolliker,* and
after him by several other anatomists, who
contend that these primitive cells might
take this, stellate form spontaneously. Our
opinion, however, is in conformity with
that of Waldeyer,f who was the first to
properly examine and describe this phe-
nomenon; though Huxley, % at a much

* Human Histology, French trans., 1869, p. 497.
f Untersuchungen liber die Entwicklung der Ziihne,
Zeitschr. f. rat. rned. 1865.

% Quart. Journal of Microscopical Sc, 1854, pp. 55-56.

OF Till". DENTAL FOLLICLE: s 1

earlier day, had advanced the idea (h\ po-
thetically, it is true,) thai the enamel-organ
had an epithelial origin ; but be did not
indicate the mode wherebj the transforma-
tion of it- elements was effected.*

Now as to the pi'ismaHc cells : duringthe

* The epithelial nature of the enamel-organ had not till
recently been accepted in France; but ita elements were
described as stellate Bbro-plastic bodies I Robin and Magitot,

loc. cit., p. 60). This conclusion was based, however, solely
upon the form that these elements present; and the same
argument may be used to controvert this opinion. It is
this: that in the enamel -organ the borders of these cells,
between the radiated filaments which are drawn out from
their periphery, are always concave, while in the stellate
fibroblastic bodies these borders present plane or convex
surfaces alternating with those that are concave.

[The student must not infer from the above that
Huxley was the first to advance the idea that the enamel
was of epithelial origin; for this opinion was held by
physiologist a Long before his day. The discovery accred-
ited to Huxley is this: that the. cells, constituting the
internal mass of the enamel-organ (the reticular portion
Burrounded by the stratum of prismatic cells), are only
metamorphosed epithelial cells. Heretofore bistologiBta
believed these to be stellate connective-tissue cells: but
the peripheral layer was then, as it is dow, admitted to be
composed of epithelial cells. Tu.]

82 THE ORIGIN AND FORMATION

early stage of evolution, we have found
them identical in character and in dimen-
sions on all parts of the periphery ; but the
moment the enamel-organ assumes a new
form, produced by the development of the
bulb, this stratum undergoes some impor-
tant modifications. At this period, in fact,
the cells of that portion of the cortical layer,
which occivpy the concave face of the enamel-
organ, and which consequently lie in con-
tact with the dentinal bulb, begin to in-
crease in length ; while those constituting
the convex surface of this organ sensibly
diminish in size. This difference in the di-
mensions of the cells occupying the. two
segments of the prismatic stratum or corti-
cal layer manifests itself more and more
during the progress of follicular evolution ;
and, as we shall see hereafter, the external
layer [" external epithelium of the enamel-
organ " disappears long before the com-
plete atrophy of the enamel-pulp ; while
the other [the "internal epithelium"] still

OF III I'. DENTAL FOLLICLE.

83

remains to perform the importanl functions
assigned to it. Qamely, tin formation of th

i mtnh I.

The prismatic cells of the concave face
of the enamel-organ [the, enamel-cells, or
ameloblasts*] offer some peculiar character-

* [The term ameloblast is compounded of Amel (from the
French Bmail), enamel; and blast (from the Greek blastos),
germ. This compound word has recently been introduced
into our nomenclature by Prof. Eames, of St. Louis; and
owing to its euphony, its concise and definite expression,
and its general relations to the terms osteoblast, odontoblast
and others, it ought, as it seems to me, to be adopted by the
dental histologist. It will certainly facilitate the descrip-
tion of the parts to which it is applied, and obviate the
repetition of long descriptive phrases. I shall, therefore,
follow the lead of Dr. Black, and whenever it seems best
shall substitute this new term for phrases of equivalent
meaning that may be found in the original. The amelo-
blasts are the enamel-cells. They constitute the prismatic
layer of Legros and Magitot; the internal epithelium of
Kolliker; and the adamantine membrane of Raschkow;
namely, that section of the stratum Malpighii forming the
peripheral layer which lines the concave face of the enamel-
organ, and lies i» immediate contact with the dentine-bulb.
The other section of this stratum covers, or rather constitutes,
the convex surface of the enamel-organ, and is generally
known as the external epithelium. It has probably been

84 THE ORIGIN AND FORMATION

istics, to whicli we will now call your at-
tention. Originally identical with those of
the [lowest layer of the] Malpighian stratum,
from which they are directly derived, these
cells, besides increasing in length, expe-
rience some important changes in form.
The extremity that is directed toward the
center of the organ, becomes long and slen-
der, forming jjrocesses which unite with or
are continuous with the filaments that pro-
ceed from those neighboring cells which con-
stitute the portion of the enamel-organ
known as the stratum intermedium* The

previously noticed that the peripheral layer has been divided
into two sections. This has been done simply for con-
venience of description, there being no anatomical division
between these two portions ; the cells being alike and con-
tiguous, although at a later period they experience those
dissimilar modifications that are fully and clearly described
in the text. Tr.] '

* [As this portion of the enamel-organ is only inci-
dentally mentioned in this work, a few words of explana-
tion may not be out of place here. It might with pro-
priety be termed the stratum of Hannover since he is its
accredited discoverer.. This "stratum intermedium" is
not represented in any of these cuts, but it consists of a

OF THE DENTAL FOLLICLE.

opposite or peripheral extremity, thai is
bo say, the bo8( of these cells, presents the
regular prismatic form of a hexagon. (Fig.
24.) It' we n<>\\ examine an underanged

[Fig. 24 represents the basal aspect of a layer of amelo-
blasts. Tu.]

layer oftlic-c prismatic cells, or ameloblasts,
magnified about 400 diameters", we shall
find that the free margin of this layer (that
is to say, the part that corresponds to the

few layers of cells that still retain nearly their primitive
form, and lies between the layer of ameloblasts and the
stellate portion of the "enamel-pulp." Prof. Tomes (in
his Man. of Dental Anat., p. 125) describes it thus: "The
'stratum intermedium' consists of cells intermediate in
character between those of the bordering epithelium and
the stellate reticulum; they are branched, bat less con-
spicuously so than the stellate cells, with which on the
one hand they are continuous, on the other with the
enamel cells." The special functions of these cells is

86 THE ORIGIN AND FORMATION

base of these cells ) appears clearer than
the bodies of the cells themselves, and in
fresh preparations seems like a continuous
line. If, however, a like examination be
made of some hardened preparations, or if
careful means be taken to detach this mar-
ginal line, which the edge of a section of the
plateau represents, from the base of the
cells, it will be found that it can be sub-
divided into as many sections as there
are cells in the layer. And yet some prep-
arations may be met with, in which more
or less of this clearer line becomes detached
in the form of a shred 'of ribbon. It is this
strip, which is evidently made continuous

questionable. Waldeyer believes that, since "the enamel
cells may be frequently seen to be connected at their
lower extremities with the cells of the stratum interme-
dium, a multiplication of the enamel- cells from the cells
of this stratum in the direction of their length may be
admitted to occur " (Strieker's Hist., p. 334); an opinion
shared by Hertz and the author first quoted, but differing
from that of Magitot and Kolliker. A further description
of these cells would more properly come under the head
of Development of the Enamel. Tr.]

OF THE DENTAL FOLLICLE. 87

1>\ artificial means, thai ha- given rise fco
the hypothesis fchal a membrane invests or
lines the concave face of this stratum of
cells, ameloblasts. AW- shall sec, moreover,
in examining these peculiarities in detail,
thai this appearance is not specially and ex-
clusively confined to the cells of i he enamel-
organ, since it exists wherever we find the
prismatic cells provided with what lias been
termed a 'plateau. The prismatic cells of
the intestines are known to be thus sup-
plied. Now it happens, that, whether this
plateau remains adherent to each c<ll s,j><i-
rateh/j or whether it becomes adherent to
those of the neighboring cells, so that a
strip may be detached presenting the ap-
pearance of a true membrane, depends en-
tirely upon the mode of treatment to which
the preparation is subjected.

I'k \.\k : This, I inter, is the basement, or pre-
formative, membrane (

Teacher: The edge of the tissue that forms,
in section/ the clear line, is not the same Btruc-

88 THE OBIGIN AND FORMATION

tnre described (p. 17) as the membrana prce-
formativa of Haschkow ; the membrane here
discussed is situated between the latter tissue
and the layer of ameloblasts ; and these two
structures, thus lying in apposition with each
other, correspond with the " double pellucid
layer" mentioned by Dr. Black, in his report
on Histology (p. 72 Trans. A. D. A., 1878),
in which he says: " Just before the calcifi-
cation, and even before the odontoblasts make
their appearance, the ameloblasts, and the tis-
sues of the pulp, are separated by a well marked
double pellucid layer ; which, in section, appears
as a double band," etc. The two white parallel
lines A, A, fig. 25, represent this "double band ";
the upper one being the tissue here described
by our authors, and which is identical with the
membrana prwfomnativa of Huxley ; while the
lower one represents the basement membrane of
Todd and Bowmann, and the membrana prce-
formativa of Raschkow. The clear line referred
to in the text as being seen at the edge of a
section of a layer of enamel-cells, — namely, the
upper line of the double pellucid zone, or the
preformative membrane of Huxley, — is formed
by the artificial union of the opercula that cover
the dentinal extremities of the ameloblasts.

OF THE DENTAL FOLLICLE. B9

The figure below is an ideal representation of
a dental follicle before it lias lost its connection
with the epidermis. The object of this cut is
to show the relation of the basement membrane
and the two different structures (one of which is

Fig. 25.

A. A.

Fig. 25. — B M, basement membrane; X, neck; S, sac or
follicular wall; 0, enamel -organ; B, bulb; E E, external
epithelium of the enamel-organ and the basement mem-
Inane: /•; ('. epithelial cord; C T, connective tissue sur-
rounding the enamel-organ; Ep, epidermis or oral epithe-
lium.

The parts embraced between the points where the di-
vergent lines A A terminate, are: — (1) the concave face of
the enamel-organ, lined with a layer of ameloblasts, or the
"internal epithelium": (2i the membrana pra-formativa of
Huxley, or the tissue compos.. 1 of the basal coverings of the
ameloblasts; (3) the membrana prseformativa of Raschkow,
or the basement membrane; (4) the dentine-bulb itself.
I diagrammatic.
7

90 THE ORIGIN AND FORMATION

known as the membrana prseformativa of Rasch-
kow, and the other as that of Huxley) to the
adjacent parts. The white line terminating on
either side of the upper portion of the figure
represents the basement membrane, and sepa-
rates the epidermal from the dermal tissues. The
mass embraced within the walls of this devious
line is composed of epithelial cells ; that found
on the other side of this line belongs to the
dermal tissue. Now, that portion of the mem-
brane represented by this line, which passes be-
tween the enamel-organ (O) and the dentine-bulb
(B), and which constitutes the peripheral layer
of the latter (A A), is said to assume important
functions in the development of the dentine; and
hence was denominated the membrana prseforma-
tiva by Raschkow; a name it still retains, although,
as to its nature and office, physiologists are not
agreed. The upper line running parallel to this
membrana pneformativa of Raschkow, as before
stated, represents the membrana prseformativa of
Huxley ; and by him, Schwann, Kolliker, Magi-
tot, and some others, special functions have been
assigned to it in the formation of the enamel.
But you must not infer from what has been said
that the last named authors precisely agree as to

OF THE DENTAL FOLLICLE. 9]

the nature of this membrane, or as to the mode
of enamel-development, amelification.

Caspeb: This term membrana prcBformativa

is about as equivocal as that of mucous mem-
brane, for I have already found it applied to
three different tissues, one of which is said to
line the walls of the pulp-chamber.

Teacher: The latter consists of a layer of
odontoblasts, and is generally called the mem-
brana eboris. But we must discontinue for the
present the discussion of these tissues, the nature
and functions of which (and even the existence
of some of them) are still matters of dispute.
Nevertheless, these histological tacts or appear-
ances will be found useful hereafter in studying
the development of the enamel and dentine.

As to the nucleus of the prismatic cells
[the cmieloblasts] of the enamel-organ, we
find that its position varies in relation to
the ends of the cell, according to the period
of development; at first it is aboul equi-
distant, bu1 it afterward appears to move
toward the tapering extremity. This ap-
parent ehano-e of place, however, ta no1 real.

92 - THE ORIGIN AND FORMATION

but results from the more rapid growth of
the dentinal end of the cell (which is re-
markably active after the development of
the bulb), thus causing the nucleus appar-
ently to move away from it. This differ-
ence in the development of the extremities
of the ameloblasts is especially remarkable
in the enamel-organ of the incisors of the
rodents, in which these elements attain to
great length.

OP 'NIK DENTAL FOLLICLE, '.».">

CHAPTER III.

ORIGIN AND FORMATION OF THE DENTAL BULB. AND OF
THE FOLLICULAR WALL.

AS we have just seen, the enamel-organ
-*--*- sooii loses its spherical form and
acquires the appearance of a hood or cap;
and this change in form is contemporaneous
with the appearance of a new component
part of the follicle, — the dentinal bulb. A
alight opacity appears on the point of em-
bryonic tissue of the jaw, that corresponds
to tlif depression in the enamel-organ.
This opacity is due to the production of
new elements, which are grouped in such a
manner as to form at first a Little rounded
nipple of hemispheric form, the convexity
of which corresponds exactly to the de-

94 THE ORIGIN AJSTD FORMATION

pression or concavity of the enamel-organ.
(Fig. 26, H.)

FIG. 26.

Fig. 26. — Vertical section taken from the incisive region of
the lower jaw of an ovine embryo, measuring 115 millimeters,
magnified 80 diameters, a, Meckel's cartilage; b, osseous
formation; c, section of the dental artery; d, epithelial
band (bourrelet); E, epithelial lamina; F, cord; g, enamel-
organ. Meckel's cartilage at the right of the cut.

H represents the incipient dental bulb. The drawing
for this cut preserves the defects in the specimen from which
it was taken. For example: the space between the enamel-
organ and the follicular wall is caused by the shrinkage of
the former, — a result of too long maceration of the parts.
Similar defects will be found in several of the following
cuts.

OF THE DENTAL FOLLICLE. '.».>

This little papilla, which represents the
incipienl dental bulb, is composed a1 firsi
only of nucleated embryoplastic elements,
and soon afterward of fusiform and Btellate
bodies. It will be noticed, also, that at
this early stage of development a vascular
loop enter- it- substance, similar to those
Pound in the papillae of the skin; but we
have not been able to discover in it any"
nerve-fibres until it has attained a mam-
millated form. The l>ull> retains this latter
form but a brief period, for it soon shows
a tendency to take that of the future tooth:
thus, for the incisors and canines, it assumes
a conical form; for the molars, in man and
the carnivora, the primitive papilla i> soon
covered with secondary protuberances, equal
in number to tin- cusps of tin future crown :
and in the compound molars of the herbiv-
ora and rodents throws out prolongations
which represent also the future divisions of
the crown. An analogous arrangemenl is
found in the incisors (d corne£) of the soliped.

96 THE ORIGIN AND FORMATION

Iii all these circumstances the enamel-
organ allows itself, as it were, to be moulded
by the bulb, so as to exactly conform to
whatever configuration the latter may as-
sume.

Casper : The dentine-papilla determines, then,
the form or contour of the crown of the future
tooth ? I inferred from a remark you made (in
regard to the supernumerary teeth, I think,)
that it was the enamel-organ that controls this
matter ; at least, that this was your opinion.

Teachee : Whatever views I may entertain
as to the influence exerted by the enamel-organ
have been mainly derived from these authors,
though I have recently given this subject con-
siderable thought. This is one of the points in
dental physiology that has been almost entirely
ignored by authors who have written upon the
development of the teeth. Drs. Legros and
Magitot, however, express very decided views
in regard to it, though they do not state the
reasons upon which their opinion is founded.
In a more recent work (Traite des Anomalies,
etc., Paris, 1877,) Dr. Magitot, the surviving
author of the present treatise, maintains, very

<>K THE DENTAL 1 OLLH I.K. 97

positively, that the enamel-organ is endowed with
this influence. These are his words:

•• It is explicitly admitted that the epithelial
cord, or enamel-organ, dominates and determines
the place and the form of the tooth. The gene-
sis and development of the dental bulb (dentine-
germ), which makes its appearance subsequently
to the cord, is absolutely dependent, as a physio-
logical consequence, upon the presence and fo?'m
of the enamel-organ itself. One will, neverthe-
less, be tempted to believe," he continues, " that
the nature of the future tooth is under the control
of the dentine-papilla, a kind of organic mould
upon which the calcific elements are grouped ;
but it must be remembered that the epithelial
cord, which represents the future enamel-organ,
always precedes the appearance of the dentine-
papilla, which never originates till the cord has
advanced a certain distance in its course. Accord-
ingly, we believe that the epithelial cord decides
Dot only the place of genesis, but the form and
function of the corresponding tooth."

It will be seen from the above quotation that
I>r. Magitot dissents from the general opinion in
regard to the influence which these parts i namely,
the enamel-organ and the dentine-germ) exercise
upon each other.

AlB for myself, I had supposed that the enamel-

98 THE ORIGIN AND FORMATION

organ was the more passive structure, and that
its form, at least, was determined by the dentine-
' papilla. But, in considering this subject more care-
fully, and examining both sides of the question,
I discover evidence which strongly confirms the
theory of Dr. Magi tot. My conclusions rest
mainly upon a certain fact in the statement of
Dursy, who, according to Waldeyer, says :

" The first germ of dentine appears in the den-
tal saculus, as a dark, semi-lunar area at the bot- -
torn of the dental groove, — that is to say, of the
enamel-germ, — coetaneously and continuously
with which it is developed along each half of the
jaw. At certain points, corresponding to the
position of the subsequent teeth, the young struct-
ure develops in the form of papillae, projecting
against the enamel-germs, while the remainder
atrophies. The two horns of the semi-lunar mass
(as seen in section) extend from the base of the
dental papilla some distance upward, and em-
brace the dentine-germ and enamel-organ." •

The particular point in this statement of Dursy
to which I allude, and to which I wish to call
your special attention, is that referring to the semi-
lunar area of tissue extending along each half of
the jaw, and from which the dentine-germs are de-
veloped. If the anatomical description of Dnrsy

OF THE DENTAL FOLLICLE. '•,'•,

is correct (ami lam not aware thai it is disputed),
a dentine-germ might be developed from any poinl
of this semi-lunar area which should be reached
by the enamel-organ. No particular point is

assigned to the development of any especial den-
tine-germ : that is entirely accidental, and de-
pends upon the course which the enamel-organ
takes.

For example : It" the epithelial cord of a cuspid
should deviate from its normal course, so as to
come in contact with this dentinal sheet of tissue
at a point between the bicuspids, the cuspid
would be developed between those two teeth. In
fact, whatever point in this tissue the enamel-
organ of the cuspid should reach, the future
tooth would be a true cuspid.

If this be admitted, the theory of Dr. Magitot
must be true, — that the enamel-organ determines
the form and character of the future tooth.

If the fact that the teeth of certain fishes are
wholly destitute of -enamel, seems to militate
against this theory, we have the statement from
high authority that all teeth, whether clothed
with enamel or not, are, in the formative stage,
universally endowed with enamel-organs. May
we not infer, then, that in such cases the rudi-

100 THE ORIGIN AND FORMATION

mentary enamel-organ has performed its func-
tions when it has incited the development of the
dentine-germ, and determined ito future form
and character?*

As the dental bulb develops in height,
it takes a slightly oblique direction in re-
lation to the axis of the follicle, and at the
same time undergoes a certain constriction
at its base, thus forming a kind of neck
at the line where (as has been already
seen) the enamel-organ is reflected back
upon itself. (Fig. 27.)

There is, however, one .peculiarity in the
structure of the bulb which we ought par-
ticularly to notice here, and that is the na-
ture of the external surface of this organ.

If you examine the structure of a vertical
section of the bulb, you will find that there
exists at the periphery of this organ a thin,
clear zone, which is easily distinguished
from the subjacent tissue by its refraction.

* [Extract from my report on Dental Physiology, read
before the American Dental Association, August, 1878. — Tit.]

OF THE DENTAL FOLLICLE. 1<»1

This zone to which several anatomists have
assigned important functions, is only a thin
stratum of amorphous material, which is
wholly destitute of anatomical elements and
of granulations.

This amorphous layer is not only more
Transparent, but somewhat denser, than the
subjacent tissue of the bulb, so that some-
times it may be detached from the surface of
the latter. This fact has led many anat< >mists
to suppose that the bulb was invested with
a distinct membrane (the memhrana pivfor-
mativa of Raschkow). (Fig. 25, lower
parallel line, A A, p. 89.)

We shall describe, in another work, the
nature and functions of this structureless
layer, but we will say this much in advance,
that it is in this tissue that the ivory-cells
[odontoblasts | make their first appearance.

As soon as this little mass of new ele-
ments, which constitutes the dental bulb,
has taken a hemispheric form, two opaque
processes, originating at its base, ascend di-

102 THE OKIGIN AND FORMATION

vergently upon its sides; these appear to
emanate directly from the tissues of the bulb
itself, and they represent the first trace
.of the wall [sac] of the future follicle.
(Fig 22 I, p. 73.)

If, at this period, the constitution of these
follicular processes be studied, we find them
composed of exactly the same elements as
the bulb from which they originate. As
the bulb continues to develop, these pro-
cesses also increase in length, and bend
round toward each other, in such a way as
to finally embrace in their double concavity
not only the bulb itself but also the enamel-
organ, which, as you already know, constant-
ly crowns the latter. In this manner the
follicular wall, which was at first only a
little collar attached to the neck of the bulb,
by its gradual upward growth finally em-
braces and isolates both the enamel-organ
and the dentinal bulb.

Caspee : We are told, at first, that the fol-
licular wall originates from two processes, on

OF THE DENTAL FOLLICLE. 1 1 >3

opposite sides of the bulb; but now it is de-
scribed as a little colla/r fixed to the neck of
the bulb — apparently quite another thing.

Teacher: These authors, doubtless, at first
describe the follicular wall as it appears in sec-
tion. In reality it must be a circular process,
which, in the diagrammatic figure, presents the
appearance of two. Prof. Tomes says, in his
Dental Anatomy : "From the base of the den-
tine-bulb prolongations pass outward and slight-
ly upward, so that they in a measure embrace
the free edge of the enamel-organ ; and, at a
somewhat later period, they grow upward till
they fairly embrace the whole enamel-organ."

Owen, in his Odontography, uses the follow-
ing language: "By the development of three
or four lamellar processes from the opposite sides
of the mouth of the follicle, and their mutual
cohesion, the papilla is inclosed in a capsule."

Prof. "\Vedl, in his Pathology of the Teeth,
says: "The dentinal germ proceeds from the
floor of the dental sac which invests it and the
enamel-organ."

K. illiker (fifth edition) says: "The dentine-
papilla arises from the bottom of the dental sac."

Although the last two authors do not minutely

104 THE ORIGIN AND FORMATION

describe the process of development, they evi-
dently do not mean that the bulb arises from the
"bottom" or "floor" of a formed sac, but upon
the surface of a sheet of tissue which finally
forms the sac. They agree with Tomes and the
authors of this work, excepting that the former
histologists believe that the base of the dentinal
bulb is inclosed within the walls of the sac;
whereas the others believe the follicle, from its
apex to the base of the bulb, to be invested by
the sac.

At this period the follicular wall may be
compared to a muff inflated in the middle,
the lower opening of which corresponds to
the base, or neck, of the bulb to which it is
attached ; while the opposite opening corre-
sponds to the neck of the enamel-organ,
that is to say, to the point where the latter
is connected with the epithelial cord. Soon
afterward the cord becomes severed at this
point, by the resorption of its constituent
elements; a cessation of continuity due,
without doubt, to the compression or stran-
gulation it undergoes from the encroaching

OF Till'. DENTAL FOLLICLE. LOS

walls, which u<>\\ unite a1 this poinl and
completely inclose the follicle. Thus fclie
enamel-organ Loses the connection which it
had hitherto maintained with the epithelial
lamina, and the dental follicle may be re-
garded as definitely completed. (Fig. 27.)

Fie. 87.

— 4C

Fig. 27. — Section of the lower jaw of a bovine embi^o,
magnified 80 diameters; showing the dental follicle, as
completed, ami the surrounding tissues.

a. Meckel's cartilage; /<. traces of ossification; r. Lowes!
8

106 THE ORIGIN AND FORMATION

This wall [sac], composed primarily, as
we have seen, of embryoplastic elements,
gradually assumes the aspect of a distinct
laminated membrane, which may be sep-
arated from the adjacent tissues, except at
the base of the bulb, to which it remains
fixed.

Kolliker, with most other authors, de-
scribes this wall as composed of two con-
centric laminge ; and yet admits, with Hux-
ley, that the transparent stratum which
clothes the bulb (membrana prceformativci)
reflects itself back on its internal face, and
thus lines the whole inner surface of the
follicular wall.

We will reserve, for a forthcoming work,
the study of these different peculiarities of
structure.

layer of the Malpighian stratum; d, oral epithelium; F,
ameloblastic layer; lower F, external layer of the enamel-
organ, — a continuation of the internal layer of ameloblasts;
g, stellate recticulum of the enamel-organ; H, dental bulb;
I, follicular wall (indistinct); K, buddings of the cord.
The vascular appearance of the bulb does not appear in the
original.

OF i in: D] xi \i. i in. i. n i.i:. 1«>7

I'uwk: With my ideas of the parts constitut-
ing the follicle, I fail to comprehend how the pre-
formative membrane can line the internal Burface
of the follicular wall and also clothe the bulb.

Teacher: Perhaps Kolliker's definition of
the follicle, assisted by Fig. 2."), may enable you
to better understand this matter; and since
it is brief, 1 will give you the benefit of it.
In his "'tli edition it reads as follows: "The
dental sacs [follicles] are composed of three
parts, — the sac properly so-catted, the dental
germ, and the enamel-organ. The proper dental
sac is an envelope consisting of two layers. — an
external one composed of dense connective tissue,
ami a softer internal one, of a gelatinous consi
ence, containing numerous connective-tissue cor-
puscles, and also some true fasciculi of connective
tissue. This internal layer is limited on its in-
ner surface, toward the enamel-organ, by a homo-
geneous layer of extreme tenuity, the preform-
ative membrane of the dental-germ'" [bulb].

At tin- period of evolution to which we
have arrived in our description, the follicle
i- completed and closed, tf now we exam-
ine it- general constitution, we shall find it

108 THE ORIGIN AND FORMATION

composed, proceeding from the outside in-
ward —

1st. Of the follicular wall which, clothes
its entire surface, — except the base of the
bulb, which remains free. (Fig. 27, I.)

2d. Of the enamel-organ, subjacent to
the follicular wall, to which it conforms in
its whole extent, in such a way that while
its external face corresponds to this wall,
its lower, concave face is in immediate con-
tact with the bulb. (Gr.)

3d. Lastly, of the hull itself, which oc-
cupies the lower and central portion of the
follicular sac. (H.)

Except the three fundamental parts just
named, no other substance finds place in
the constitution of the follicle. The enamel-
organ exactly fills all the space compre-
hended between the wall [sac] and the
bulb, and terminates at the base of the lat-
ter in a rounded margin, which forms the
dividing line between the prismatic cells
that clothe both its concave and convex

OF THE DENTAL FOLLICLE. L09

surfaces | Sec Fig. 25, A A |. This bound-
ary, however, is nol artificial. It results,
on the one hand, from anatomical differ-
ences that these parts now present, and,
on the other, from the physiological role
which the cells of the concave face are
called upon to perforin: whereas the exter-
nal layer atrophies rapidly and disappears.*
This prismatic layer of the concave surface
(adamantine membrane), constituting, as we
shall see, the stratum of enamel-cells | amel-
oblasts], remains a long time in the compo-
sition of the follicle ; not only after the ex-
ternal layer has disappeared, but even after
the atrophy of the gelatinous part of the

* I Waldeyer and Hertz believe this external layer of the
enamel- organ, instead of being absorbed, to finally become
the cuticula dentis, " Nasniyth's membrane." Tomes, Magi-
tot and Wedl, however, attribute this membrane to another
source, believing its origin identical to that of the cement;
while Huxley maintains that the preformative membrane
(see upper line, A A. Pig. 85), after the enamel is completed,
constitutes this thin enamel covering. Though Kolliker
does not assent to the latter theory, yet he believes this
membrane to be a product of the enamel-organ. — Tb. |

110 THE ORIGIN" AND FORMATION

enamel-organ. Let us farther add, that in
the rodents (whose incisors, as we know, are
of continuous growth) this layer of cells
[ameloblasts] remains upon a portion of the
anterior or convex face of these teeth dur-
ing the entire life of the animal.

This constitution of the follicle, compre-
hending, as it does, these three fundamental
parts, seems to be characteristic of that of
man, of the carnivora, and in general of all
the mammals whose teeth are not supplied
with coronal cement. But if the follicle of
an embryonal soliped be examined, it will
be noticed that for a long time before the
formation of the first dentine-cap there ex-
ists between the follicular wall and the or-
gans within it a new tissue, very distinct
from the neighboring parts — in color, in
consistence, and in composition. This is
the organ upon which will subsequently
depend the formation of the cement. We
will omit the description of the cemental
organ here, but will study it elsewhere in

OF THE DENTAL I •'< LLIOLE. 1 1 1

detail; all that we wish to establish at
presenl is its incontestable existence in the
follicles of Buch teeth as are clothed with
corona] cement.*

This fact is so decisive that by the simple
examination of a follicle we can determine,
from the presence or the absence of this
organ, whether the future tooth will or
will not be furnished with coronal cement.

The dental follicle, the component parts
of which are all thus grouped and inclosed
in one sac, has a general ovoid form. Its

* This cemental-organ, which will always be found in the
follicles of the molars of herbivorous animals, and in those
of the incisors and molars of solipeds, has been described
for the first time in France, in a work by E. Magitot, enti-
tled " Derelopvment de la Structure des Dents." (These in-
augurate, 1858, p. 80). It was presented anew some years
ater by Robin et Magitot. (Loc. Cit. 1861, p. 145 et suiv.)
Since that time the existence of this organ appears not to have
been recognized by any other anatomist. Indeed, in the
last works published in Germany, by Kdlliker, Waldeyer,
Hertz. Kollmann and others, its existence lias been formally
denied. We are greatly surprised to see so evident an
anatomical fact thus contested; but it will be easy for us to
establish again the reality of this discovery, which we pro-
pose doing in our second memoir.

112 THE ORIGIN AND FORMATION

size varies greatly in the different animal
species, and according to the kind of teeth
that are to be developed from it. When
the follicle is completely formed, it remains
inclosed within the embryonal tissues of the
jaws, with which at first it is only feebly
connected. Thus isolated in the depth of
the jaws, having lost its communication
with the mucous membrane [epithelium],
by the rupture of the cord, it does not yet
form any connection with the maxillary
bone; for the formation of the alveolar
partitions does not take place until a later
period.

The net- work of vessels which ramify the
follicular wall and dental bulb is furnished
from different sources, and enters these
tissues from the surrounding parts; while
the enamel-organ, as we know, is non-
vascular. The direction of the follicle, that
is to say the great axis of the ovoid, which
it represents, is quite variable. Though
regularly vertical in man and the carnivora,

OF THE DENTAL FOLLK LE.

1 L3

ii takes an oblique direction in the herbiv-
orous animals, and this i> more particularly
marked in the follicles of the incisors. The
latter, in fact, take an oblique and diver-
genl course, like the spoke- of a wheel,
which is moreover in conformity with the
inclination of the alveolar arch. (Fig. 28).

A

rff.rfi

My

MP

Fig. 28. — Vertical section of anterior portion of the lower
jaw of an equine embryo, magnified 80 diameters.

a, Meckel's cartilage; b, traces of ossification; d, oral
epithelium; g, enamel-organ; //, dental bulb; /, layer of
ameloblasts (internal epithelium); K, permanent follicle;
L, place assigned for the development of the cement.

114 THE ORIGIN AND FORMATION

We may add, however, that the axis
of the follicle is generally the same as
that of the bulb, and that it strictly corre-
sponds with that of the alveolar border, for
each particular species. As to its position
in the jaws, it differs in like manner accord-
ing to the species. In man, the carnivora
and the solipeds, it is situated quite near
the mucous membrane [epidermis], and in
these the epithelial cord is consequently
quite short; but it is located more deeply,
in the bovine and ovine herbivora (cattle
and sheep), and the cord consequently ac-
quires a proportionate length.

OF THE DENTAL FOLLICLE 1 1 5

CHAPTER IV.

PHENOMENA THAT FOLLOW THE FORMATION OF THE
FOLLICLE, AND THE RUPTURE of THE EPITHELIAL
CORD.

AS soon .-is tin* sac is closed, ami rh<- follicle
-*--^- becomes isolated by the rupture of
the epithelial cord, various phenomena are
produced in the embryonal tissues that sur-
round this organ, in the region between the
summit or apex of the follicle and the epi-
thelial layer of the gum. These phenom-
ena are principally located in the epithelial
lamina and in the cord itself.

In fact, as soon as the epithelial lamina
loses its connection with the follicle, by the
rupture of the cord, the epithelial cells
composing it become greatly increased in
number at the severed point. This multi-
plication of cell-elements results in the
format ion of irregular buddings, which

116 THE OEIGIN xVND FORMATION

wander in different directions into the
deeper portions of the embryonal tissue.
These buddings vary greatly in form ;
sometimes they are simple cylinders, retain-
ing their connection with the primitive
lamina by pedicles of various lengths, and
sometimes this slight connective is ab-
sorbed, thus isolating an epithelial mass.
(Fig. 19, F, p. 67.)

These masses are formed wholly of large
polygonous cells, similar to those found in
the center of the epithelial lamina; but
they are never, like the latter, surrounded
by a layer of prismatic cells. Very fre-
quently, however, groups of these elements
take the globular form, and are, in every
respect, similar to those which are some-
times discovered within the epithelial lam-
ina itself. (Fig. 29, F.) These different
dispositions account for the presence of
epithelial masses of such varied form ;
which, until now, were unexplained, and'
which are found in almost all the sections
of the jaws made at this epoch of evolution.

OF THE DENTAL I'M. I. KIT.
Km;. 29.

117

*2i „ tw$jS r

Fig. 29.— This is a section taken from an embryonal
calf. (Magnified 260 diameters.) Like fig. 19, it embraces
the region external to the follicle (a), which latter is no!
shown on the cut; b, epithelial buddings upon the follicular
wall; EE, buddings of the epithelial cord; /■'. globular
epithelial mass in the lamina; ii, oral epithelium (epidermis);
c, epithelial lamina " still intact."

118 THE ORIGIN AND FORMATION

These phenomena of buddings cease at a
certain period, which always seems to be
anterior to the time at which the dentine
makes its appearance in the follicle ; and
then all the epithelial fragments, and the
lamina itself, undergo gradual absorption,
and entirely disappear before the develop-
ment of the tooth is perfected.

Coincidently with the phenomena thus
effected at the expense of the ejrithelial
lamina, a series of modifications jDrecisely
analogous transpires also in the severed cord
itself. From the remnants of this cord,
buddings, or processes, issue, which, at
times, are very numerous ; as we have wit-
nessed, for example, in certain preparations
taken from the jaws of bovine embryos.
These phenomena continue for a consider-
able length of time, since they can be ob-
served up to a period even verging on the
eruptive stage. The general form of these
buddings may vary; sometimes they pre-
sent somewhat the appearance of a bouquet,

OF THE DENT \i. FOLLICLE. I I 9

(ihc Pool corresponding to the summit of
the follicle,.) which spreads, open- and con-
tinue- to expand till it reaches the vicinity
of tlif epidermis ( Pig. 27, K ) ; a1 other times
tlic\ form, by a multitude of reciprocal
anastomoses, a perfect net-work (Fig. 29,
E E), in tin- nii»l>t of which are still found
some isolated masses.

Hut these differently grouped or anasto-
mosing buddings <!<> n<>t all follow the di-
rection of the lamina, nor of the cord; in
fact their general tendency is evidently
toward the surface of the mucous mem-
brane.

The del>ris of the cord are invariably
composed of small polyhedral cells lying in
juxtaposition to each other, and exactly
similar to those of the cord itself; bu1 the
cells composing these debris, like those of
the remains of the lamina, are never in-
vested with a layer of prismatic cells.

The buddings of the cord are also of
variable size: some are extremely slender,

120 THE ORIGIN AND FORMATION

and composed of a single string of cells;
others assume a strumous or swollen form,
and contain several superimposed layers of
these elements; but the large cells and
the globular masses — the presence of which
we have recognized in the debris of. the
lamina — are never found here.

The remains of the cord, like those of
the epithelial lamina, after undergoing these
multiplications, become gradually absorbed,
and disappear, as was previously stated, at
or about the period of eruption.

While these j)henomena of buddings are
taking place, at the expense of the debris
of the cord, it will be noticed that a similar
process is going on at the exterior surface
of the follicular wall. These two series of
phenomena, as well as those that take place
in the lamina, are simultaneous."*

In fact, if a vertical section be made of
the region comprised between the summit

* All this array of facts has been presented for the first
time in France, by Robin and Magi tot. (Loc. cit., I860,
p. 74.)

01 THE DENTAL FOLLICLE 12]

of .-i follicle and the external surface of the
epidermis, shorl ly after the rupture of I he
cord has taken place, it will be seeu thai
tlir remnants of this cord even extend t<>
and mingle with some of the proliferations
which arc adherenl bo tin- wall | sac |. These
have the most varied forms; mostfrequently
they are club-shaped expansions, or <-\ lin-
ders of different lengths, terminating in a
rounded extremity; and sometimes pro-
vided with a kind of pedicle. They cover
nearly the whole surface of that hemisphere
of the follicle which is presented toward
the epidermis. These buddings, however,
are most abundant at the apex of the fol-
licle [the point where the cord was at-
tached], and they gradually diminish as
they descend upon its sides. They anasto-
mose transversely both with each other and
with those that are attached to the cord:
and in such a way that by simply examin-
ing the surface of the follicle, without mak-
ing a vertical section, we perceive a kind

122 THE ORIGIN AND FORMATION

of plexus with very irregular meshes, super-
posed upon the follicular wall. (Fig. 29, b.)

The auatomic structure of these bour-
geons [or prolongations] on the surface of
the follicle differs in no respect from those
which we have indicated in the proliferations
of the cord, being composed of the same small
polyhedral cells minus the enveloping pris-
matic layer. This identity of structure results
from the fact that these epithelial masses
are derived from the remains of that portion
of the cord which is in the nearest proximity
to the follicle, and which by proj3agating
themselves thus finally constitute this retic-
ular covering of the follicle.

All these phenomena of epithelial pro-
liferations relate, therefore, to one and the
same process. Commencing with the lam-
ina, these buddings extend to the cord, and
finally even to the surface of the follicular
wall; they are connected with each other,
possess the same anatomical constituents,
and all finally disappear by absorption [un-

OF THE DENTAL FOLLICLE 1 23

lesa it be some masses that may become fche
enamel-organs of supernumerary teel ii. ( See
]». 66.)— Tb.]

Wo ha. ve indicated in fche foregoing fche
period at which fche phenomena of budding
commence, namely, when fche epithelia] cord
lias finished its course, having conducted
fche primitive enamel-organ to that point
where its subsequent evolution will be ef-
fected, and soon after the formation of the
secondary follicle; [in other words, immedi-
ately after the rupture of tlfe cord of the
primitive follicle]. The time of their dis-
appearance varies in the different species of
animals. In the human embryo the remains
of the cord of the primitive follicles may be
found even after the formation of the fol-
licles of the permanent teeth, and it is prob-
ably during the process of eruption that
these buddings become atrophied: in fche
canine embryo fche facts are nearly fche same:
in fche bovine and ovine embryos (calf and
lamb), it has seemed to ns thai these pro-

124 THE ORIGIN AND FORMATION

liferations disappear at a correspondingly
earlier stage ; and we think it safe to say
that, as a general rule, the complete absorp-
tion occurs toward the period of eruption.

The physiological signification of these
phenomena appears to us difficult to deter
mine. We have no personal opinion to ad-
vance in this regard ; nevertheless we will
say that, considering their mode of evolu-
tion and their structure, no glandular char-
acter whatever can be attributed to them,
as some have supposed.*

* Serres, as is known, described what he supposed to
be special glands, tartaric glands, in the mucous mem-
brane; and his views were supported by Kolliker, Todd
and Bowman, and others. The anatomical nature of these
epithelial masses, and the fact that the production of tartar
is connected with quite different phenomena, leaves no
foundation for this hypothesis.

[I have not the works of Todd and Bowman at hand,
but think Legros and Magitot must be mistaken in regard to
the opinion of these authors upon this subject. As to the
views of Kolliker, in the fourth edition of his Microscopical
Anatomy, speaking of the "gum in the foetus, " he says:
"The bodies of the size of a millet-seed, contained in it,,
described by Serres, the so-called glandulce tartaricai,
which are supposed to secrete the tartar of the teeth, are

<>l THE DENTAL FOLLICLE. 125

While the modifications jusl described
are being effected at the expense of the
epithelial debits of the cord and the lamina,
the embryonic tissue in which the follicles
arc immersed also changes it- nature, and
some Laminated elements appear therein,
forming a Loose and transparent aet-work.

The osseous tissue of the jaw (no trace,
of which is seen at the time of the origin
of the primitive cord) makes its first ap-
pearance near the base of the follicles,
where it soon forms a horizontal layer,
separating the groove of the follicles from
the canal reserved for the vessels and
nerves. Lateral processes then arise from
this Layer or floor, and form the groove in

aggregations of epithelium, and probably pathological,"
In his fifth, in place of the words " and probably patho-
logical," the following are substituted: "which, according

to my recent observations, are the remains of the embry-
onal germ of the enamel-organ" [i.e., of the epithelial
lamina]. The views of Kdlliker, and Legros and Magitot
are then precisely the same on this point, so tar as they
are expressed in these works, the only difference being in
the form of expression. — Tk.J

126 THE ORIGIN" AND FORMATION"

which the follicles lie for some time with-
out being separated by transverse parti-
tions. But later, after the development
of the crowns of the teeth has commenced^
bony processes are thrown across this
groove, forming cells for the lodgment of
each follicle, with an opening toward the
epithelial surface.

A rich vascular network of tissue 'sur-
rounds the follicle, and ramifies the sub-
stance of the walls even to the surface of
the enamel-organ, but does not penetrate it.

The vessels of the bulb are entirely dis-
tinct, forming no anastomosing connection
with the preceding plexus. We shall, how-
ever, have occasion to refer to these particu-
lars hereafter, in treating of the morphology
and structure of the follicle.

OK IIIK DION I'M- lol.l.irl.K. 1 -7

CHAPTER V.

THE PLACE, AM) MODE OF ORIGIN, OF THE FOLLICLES
OF THE PERMANENT TEETH.

r I T 1 1 E origin of the follicles of the per-
-■- manent teeth is a problem that 1ms
received particular attention from the more
recent authors who have studied the evolu-
tion of the teeth. It is one which we also
have examined with the greatest care and
]>;itience; and we believe we have suc-
ceeded in sol vino; it correctly.

Since the publication of the works of
Goodsir — in which that author held that
the follicles of the permanent teeth arise
from a fold of the sac of the primitive
follicle — most anatomists have adopted his
theory without examination or verification.
This doctrine is no more in conformity
with the tacts than is the theory that the

128 THE ORIGIN AND FORMATION

sacs of the temporary teeth are formed by
an inversion of the mucous membrane. We
have already given our views in regard to
this hypothesis, and we will refer to it
again at the close of this work. The
theory of Goodsir will be found as errone-
ous in regard to the permanent as it is
to the temporary teeth.

We ought to mention, however, that
Kolliker and Waldeyer have come near
the truth in indicating and illustrating
certain prolongations of the primitive cord,
which are destined to become the secondary
cord. But in the most recent work pub-
lished in Germany, that of Kollmann, the
preceding interpretation is not adopted.*
According to the views of this anatomist,
the cord of the permanent teeth arises from
the remnants of the primitive cord, which,
after its rupture, produces those several
buddings or epithelial masses which we
have already described. He believes that

* Kollmann, loc. cit., p. 162, etc.

OF THE DENTAL FOLLICLE. 1 29

the enamel-organ of the permanent fcooth
originates from a mass of those epithelial
fragments. In a Like manner he accounts
for the production of the supernumerary
teeth.* This new theory is equally errone-
ous; and if this German author lias been
deceived by certain natural appearances,
which might favor his opinion, it is because
he has neglected to follow out strictly, in
their successive physiological phases, the
phenomena of this special evolution.

Furthermore, the origin of those perma-
nent follicles that have been preceded by
corresponding temporary ones, is altogether
different from that of those which had no
such predecessors; so that while all of the
twenty follicles of the permanent teeth that
succeed the twenty temporary ones have a
like origin, the twelve other foUicles (the
molar- of the adult) have a different mode
of genesis. | I'>\ this these author- mean, as
will lie -ecu hereafter, that (ill the enamel-
Bee note. pp. 65-6 of this work. — Tk.]

130 THE OBIGIN ATSTD FORMATION

organs of the permanent teeth except those
of the first molars, originate from the epi-
thelial cords of other follicles, and not di-
rectly from the epithelial lamina itself. —
Te.]

The facts we are about to advance have
been gathered from the examination of a
large number of mammalian embryos, com-
prising a series of successive phases of de-
velopment. In studying microscopical sec-
tions taken from the jaws of human embryos
measuring twenty centimetres from crown
to heel, a bourgeon will be found at the
point where the primitive cord merges into
the enamel-organ of the temporary tooth.
The general form of this bourgeon is cylin-
drical, terminating in a somewhat enlarged
extremity, which gives it a clubbed or gourd-
like shape at this stage of evolution (Fig.
30, K), and may be seen quite distinctly
with a low magnifying power of 100 to 200
diameters. [Fig. 22, K, represents this bour-
geon at an earlier period]. It takes a general

OF THE DENTAL l< l.l.h l.K.

i.;i

vertical direction, and passes between the
osseous alveolar wall and the primitive fol-

PlG. 30. — Section of the lower jaw of a human embryo,
total length 30 centimeters, or about 8 inches; taken from
the region of the follicle of the temporary molar (magnified
80 diameters).

A', cord of the permanent follicle, "emanating" from
that of tin- temporary molar; /•.'. eriamel-organ; /•'. cord of
the temporary follicle; //. dentine-bulb; /. follicular wall:
«, Meckel's cartilage: r (upper), section of the dental artery:
c (lower I. that of the dental nerve; d, epithelial cells.

132 THE ORIGIN AND FORMATION

licle, along the internal or lingual face of
the latter. The elements of which it is com-
posed are the same as those of the primitive
cord, of which it is in reality only a divertic-
ulum or out-growth ; that is, of polygonons
cells covered with a single layer of prismatic
ones.

This bourgeon or bud represents the be-
ginning of the permanent tooth ; and after-
it has become sufficiently developed, one
can easily follow the subsequent phenomena
of which it is the seat. It sinks to the bot-
tom of the osseous dental groove, where it
soon loses its connection with the primitive
follicle, though still retaining its communi-
cation with the lamina ; while the primitive
follicle, by the severance of its cord (which
takes place just below the point where the
secondary cord branches off), becomes iso-
lated from its epithelial connection and con-
tinues its individual evolution. (Fig. 31.)

It was, doubtless, by examining the jaws
at the stage of development just referred to,

OF NIK DKNTA I- FOLLICLE.

L33

without taking into accounl the earlier and
Later phases, that led to the belief thai the
cord of the permanenl teeth emanated from

l'i... 81.

Fie 31. — Section of tin- lower jaw of a human foetuB,
23 centimeters in length [or 01., inches; corresponding to
about the 18th week].

K, cord or bourgeon of the permanenl follicle; L, point
where its separation from the primitive cord is being
effected: g, enamel-organ; //. bulb; c, section of the dental
artery; b, traces of ossification; c, (lower) nerve; a, Meckel's
cartilage.

134 THE ORIGIN AND FORMATION

the debris of the primitive cord, or directly
from the epithelial lamina. (Fig. 32, K.)
The descent of the secondary bourgeon

Pig. 32.

Zr--:^-— rs %m^_

^B-l)

Fig. 32. — Vertical cut of the lower jaw of a human foetus,
measuring 47 centimeters [18^ inches, and corresponding
to about the 39th week of gestation]. This figure represents
a section passing through the follicle of a bicuspid. K' K',
epidermal masses; K, debris of the secondary cord; g, en-
amel-organ; H, bulb; b, bone of the jaw; d, epidermis.

OF THE DKNTAL FOLLtt LB. 1 35

into the dental groove is soon followed by
the entire Beries of phenomena which are
common to everj follicular evolution, . . .
[and which are precisely the same as those
already described for the primitive bour-
geons. | ( Pig. 32, K.)

While these phases of development are
being accomplished, certain modifications
occur in the parts which Burround the prim-
itive follicle. The stump of the ruptured
cord, which remains attached to the prim-
itive follicle, becomes the source of those frag-
mentary growths and buddings which have
been described at considerable length in a
preceding paragraph. These phenomena
commence in the human embryo when it
has attained about twenty-three centimeters
[or nine and one-fourth inches] in length,
about the fourth month. These phenom-
ena, which always commence front the mo-
ment the cord is severed, seem to occur in
the embryos of other mammals a little
earlier, relatively, in tin1 period of gesta-

136 THE ORIGIN AND FORMATION

tion. This is the case in equine and bovine
embryos. Besides, in the lower animals
the secondary bourgeon emanates from the
primitive cord at a point a little farther
from the primitive follicle than in the hu-
man species. This is also the case in the
ovine embryo.

Casper : I have just been reading a treatise
styled the Anatomical, Physiological and Mi-
croscopical Researches on the Teeth, by Dr. J. E.
Oudet, a French writer, whose opinion, it seems
to me, is entitled to considerable respect. He
most emphatically denies that any of the perma-
nent follicles are derived either from the cords or
from follicles of the temporary teeth ; on the
contrary, he claims that they emanate, directly
and independently, from the " mucous mem-
brane." It seems very strange that there should
be such wide differences of opinion in regard to
a simple anatomical fact.

Teacher: Nearly all of the most eminent
histologists of the present day, — Tomes, Kolliker,
Waldeyer, Frey, Owen, Wedl, and I know not
how many others, entertain essentially the same
views in regard to this phenomenon as are here

OF THE DENTAL FOLLICLE. 137

set forth by Drs. Legros and Magitot. There are,
however, a few distinguished writers, foremost
among whom is the author you named, who
believe that all the permanenl teeth originate
independently of the temporary set. Then,
# again, we have one histologist, our neighbor, Dr.
(t. \r. Black, of Illinois, whose extensive obser-
vations in this direction have convinced him
that, although tin- epithelial c<>r<ls of the twenty
anterior permanent teeth generally arise front
those of the temporary follicles, yet that they
do sometimes emanate directly from the epi-
thelial lamina. It would appear from fig. 30,
and also fig. 31. in the Summary of Illustra-
tions (drawings of which were kindly fur-
nished me by this gentleman), that his
views are demonstrated beyond question. The
histological specimens from which these draw-
ings were taken have been examined by my-
self and others; and, saving a few minor and un-
important details, they are faithfully represented
in these cuts. I have the assurance of Dr.
Black that these were taken by himself from
the inciswi region of different human embryos.

In these figures the epithelial COl'ds of the

permanent follicles appear to emanate directly
10

138 THE ORIGIN AND FORMATION

from the lamina; in figs. 32 and 35, from the
•epithelial cord ; and in figs. 26, 27 and 28, from
the primary follicle itself, rather than from its
eord. (For these five figures, also, see Summary.)
If all these figures are true representations of
the parts themselves, the secondary cord may
emanate directly from either the lamina, the
cord, or the follicle itself.

Now, one word as to the place of origin of the
third permanent molar. I am not prepared with
any positive proof that this does not emanate
from the source attributed to it by the authors
of this work, and also by the several eminent
authors first named, except Wedl. In closing
these remarks I will only say that when I con-
sider the distance and the direction that this
cord must pursue, — starting from the point on
the lamina from which the first molar arises,
and extending in a backward, horizontal line
fo the spot where it eventually is developed;
and, when I take into account the period of
time that this cord must retain its normal
attachment to this remote point in the epithe-
lial lamina before the development of this
follicle commences, — which cannot be less than
three and one-half years; and when I add to

OF THE DENTAL FOLLICLE. 1 39

these t'aets the great morphological changes
that occur in the neighboring and rapidly-de-
veloping parte during this long interval of
time; — in view, I say, of all these unfavorable
circumstances, I am not prepared to accept
the theory advanced by these celebrated anat-
omists in regard to the origin of the wis-
dom teeth, without more positive evidence to
sustain it. My own observations on this sub-
ject have not been conducted with sufficient
scientific accuracy to justify me in placing my
conclusions (or convictions) on record here; but
I hardly need say that these points in embry-
onal histology require much careful revision.

Some differences are observed also as
regards the direction of this secondary
cord in the different species. Thus, while
in the human embryo we have noticed
that it takes a vertical direction, in those
of the herbivora it follows a very ob-
lique course; so that from the external
side (not far from its connection with the
epithelial lamina), passing above the tem-
porary follicle, it pursues a curvilinear route

140 THE ORIGIN AND FORMATION

to the internal or lingual face of that
follicle. This arrangement of the parts
may be seen clearly defined in sections
taken from the incisive region of bovine,
ovine and equine embryos.

The point upon the primitive cord from
which this secondary bourgeon emanates,
as also the direction it takes, are not neces-
sarily governed by the length of the sec-
ondary cord ; for in the human embryo, al-
though its direction is vertical, it is longer
than in the equine, in which it takes a cir-
cuitous course. As a general rule, its
length is governed by the height of the
alveolar border and the direction of the
primitive follicle. In man and the car-
nivora this height is relatively more con-
siderable ; and besides, the great obliquity
that the primitive follicles of the incisors of
the herbivora assume, allows the secondary
bourgeon to cross directly over the maxilla,
'and to place itself, after a very short pas-
sage, on the internal side of the primitive
follicle, where its evolution is completed.

OF ill 1-: DENTAL FOLLICLE. 141

The cord of the secondary follicle, in it>
descent into the jawsj always assumes a
spiral form, and thus perfectly resembles
the duct <>t" the sudorific gland in the
epidermis. This special disposition is so
marked a characteristic in the secondary
cord, that it may be readily distinguished
from the temporary cord: for though the
latter describes some sinuosities in its
course, it is never so distinctly spiral
as the former. The necessity for this
greater spvraMty in the cord of the perma-
nent follicle may be explained l>v the fact
that it must traverse the more developed
tissue of the jaw to a greater distance in
attending this follicle in its passage to a
point beneath that of the temporary tooth;
[and also to allow the rapidly developing
parts to increase the distance between the
follicle and the epithelial lamina, without
straining the cord or disturbing the parts
I" which its two ends are attached. — Tr.1

The spiral character of the secondary

142 THE ORIGIN AND FORMATION

cord is especially obvious near its point of
origin, and in the first half of its course ;
but toward its terminal extremity it dimin-
ishes, and finally disappears entirely, giving
place to a rounded club-shaped enlargement
exactly like that which we have described
at the extremity of the primitive cord.
This enlargement or expansion represents
the enamel-organ of the permanent tooth.

When the series of evolutionary phenom-
ena has brought the new follicle to the
period in which, in the human embryo, for
example, the bulb becomes wnicuspid for
the canines and incisors and multicuspid for
the molars, the epithelial cord, which has
already been sometime severed from the
primitive follicle, becomes in its turn rupt-
ured. From this period the secondary fol-
licle, as well as the primitive, is found iso-
lated from all connection with the epithelial
lamina during the subsequent phases of its
evolution.

This rupture is soon followed by new

OF l III DENTAL FOLLICLE. 14.*'.

subdivisions in the substance <>t the cord
itself, which seems to separate into frag-
ments of various sizes. These fragments
Lengthen and l>u<l in different directions
to such a degree thai these epithelial pro-
cesses ;ir<- mingled and confounded with
those of the primitive cord, anastomosing
with them, to form in this region a sort of
plexus, sometimes quite close, and which
extends .veil to tlie buddings that cover the
follicular wall. Finally all these epithelial
mas-.--, after having thus proliferated and
" vegetated,15 atrophy and disappear.

Such is the mode of genesis of the fol-
licles of those permanent teeth which are
preceded by corresponding temporary ones.
Twenty of the teeth thus originate. But
we find that the first teeth that appear
behind the deciduous sel are produced 1>\
an entirely different mod'- of genesis. The
first permanent molar, the follicle of which
become- considerably developed in foetal
life, is derived from an epithelial cord which

144 THE ORIGIN AND FORMATION

originates directly from the epithelial lamina.
This cord penetrates the foetal tissue in a
region where no follicle has preceded it.
(Sum, of Illus., Fig. 39.)

The origin of the second molar is similar
to that of the first twenty permanent teeth,
the follicle being produced from a diver-
ticulum or outgrowth of the cord of the
first molar. In this respect the second mo-
lar sustains the same relation to the first,
that the permanent tooth does to the cor-
responding deciduous one. But they differ
in the direction taken by the epithelial
cords ; for, while those derived from the
cord of the temporary follicle pass over- the
lingual face of the latter to a point beneath
them, that of the second molar takes a hori-
zontal course for some distance, and then by
an inflection takes its position at the posterior
side of the follicle of the first molar, where
it is developed in a line with those anterior
to it, (Sum. of Illus., Fig. 35.) As regards
the last molar, or tvisdom tooth, its origin is

OF THE DENIAL FOLLICLE. I 15

effected in a manner similar to thai which
we have just described ; thai is, the epithelial
cord that produces its enamel-organ is an

emanation from the cord of the second molar.
We must acknowledge, however, that in
determining the origin of this tooth we

have encountered many difficulties, owing

to its position and to the alteration in the
tissue-, caused by the many reactions to
which the jaws, after they have acquired
considerable size and hardness, must neces-
sarily be submitted. And yet, we have, in
several cases, been enabled to determine,
with almost positive certainty, that the
cord of the wisdom tooth originates in the
manner we have already indicated. From
these observations we perceive that, while
the first molar originates, as we have seen,
from the epithelial lamina itself, it becomes,
through the medium of its cord, the source
from which the follicles of the succeeding
molars are derived.
However this may be, with these excep-

146 THE ORIGIN AND FORMATION

tions in the mode of genesis of the follicles,
all the evolutionary phenomena are iden-
tical, to whichever dentition they may be-
long; nevertheless the order in which their
evolution is accomplished and the duration
of their physiological phenomena differ.
For, while the follicles of the first dentition
are developed during the period embraced
between the latter part of the third month
of gestation and the beginning of the fourth
war (within forty-two months), most of
the follicles of the second dentition require
a much longer time for their evolution.
For example, though the follicle of the
first molar makes its appearance in the fif-
teenth week of embryonal life (and only a
few days after the most of th<:»e of the first
dentition ). yet it d<>es not complete its evo-
lution until about the sixth year. We see,
therefore, that though the evolutionary
phenomena of the follicles are identical in
other respects, they cover periods that vary
according to the nature and the temporal)
or permanent character of the future teeth.

OF TIIK DKNTAL FOLLICLE. 147

CHAPTER VI.

CHRONOLOGY OF THE DENTAL FOLLICLE, OR THE PERIODS
IN WHICH ITS SEVERAL COMPONENT PARTS APPEAR.

TN pursuing our researches on the mode
-*" of formation of the dental follicle in
mammals, we have constantly kept in view
one important question, namely, the deter-
mination of the periods at which the sev-
eral organs that enter into its constitution
make their appearance. This study has
necessitated the careful examination of a
large number of embryos, both human and
of the principal domestic mammals. An-
other fact to be ascertained was, the exact
age of the subjects upon which our observa-
tions were made. This, in the absence of
positive evidence as to the period of concep-
tion, must, in most eases, be determined by
measurement. Xow. while the relation be-

148 THE ORIGIN AND FORMATION

tween the size and the age of the human
embryo has been determined with great
accuracy, by the aid of statistics collected
from the reports of various authors ; yet, up
to the present time no sufficiently accurate
data of this nature have been given con-
cerning the other species of mammals in
their successive stages of embryonal life.
In the human species, (the study of which
affords us more interest than that of any
other, and may be more usefully applied,)
we have made numerous observations upon
a series of embryos measuring from 8 to
37 centimetres \\\ to 15 inches] in length,
i.e. from the seventh to the twenty-eighth
week of intra-uterine life. From these we
have been enabled to fix all the periods
of the evolution of the follicles of the first,
and some of those of the second, dentition.
We have established the other phases of
the second dentition by the study of sub-
jects in the later stages of fcetal life, and at
different periods after birth.

OF THE DENTAL FOLLICLE. 1 4!>

The smallest of these embryos, thai of
3 centimeters | 1 J inches], (seventh week,)

from which we have made vertical sec-
tions through the entire Pace (Pig. 7).
has enabled us to determine that at this
period no point of ossification is yet found
upon any part of the cranium or of the
face; the lower jaw alone presents some
rudimentary osseous arches in tin- vicinity
of Meckel's cartilage. This fact is in con-
formity with the observations published in
n memoir on Meckel's cartilage, in 1862, by
Drs. Robin and Magitot.

At this period in embryonal lite the jaws
otter nothing for our consideration, relating
to the evolution of the follicles, except the
epithelial band, which is Pound to be alike
in both jaws (Fig. 7), ami which we have
already described. The follicle has not as
yet appeared in these rudimentary parts,
nor even the first trace of the epithelial
lamina.
The second embryo submitted to our

150 THE ORIGIN AND FORMATION

observation was 5^ centimetres* [2£ inches]
in -length, say of two months. From this we
ascertain that the formation of the dental
groove commences at this period of develop-
ment, and that the epithelial cords represent-
ing the enamel-organs are very clearly de-
fined ; the dental bulb has already made its
appearance as an opaque point in the region
previously designated as its place of origin.
This period of development, compared with
the preceding, has enabled us to fix the
time of the appearance of the epithelial
lamina between the seventh and eighth
weeks of embryonal life; and the genesis
of the enamel-organ from the epithelial
cord, about the eighth week.

Moreover, from these examinations we
have been able to determine the important
fact that development progresses at the
same rate in both jaws, as well as in all the
follicles of the first dentition, whether
they be of the incisors, the canines or the

* [A centimetre = 0.39371, or say \ of an inch; a milli-
metre is TV of this, or ^ of an inch.— Tr.

OP THE DENTAL FOLLICLE. L51

molars. Upon a third embryo, which
measured 71 centimetres [3 inches], cor-
responding to the eleventh week, we dis-
covered thai the stages of development
for each of the follicles of the first den-
tition were identical, and that the bull)
had become uni-eit.yid for the incisors and
canines, and rmdti-ciLspid for the molars.
The walls which had already risen from
the base of the bulb were not yet united
at the summit of the follicle, and the epi-
thelial cord was still entire. The bulb
now consists of amorphous matter inter-
spersed with nuclei, though its external
surface presents a membranous appearance.
The enamel-organ is distinctly stellated, and
the cells that constitute the external epi-
thelium are becoming smaller as compared
with those of the internal epithelium [the
ameloblasts]. No trace of the secondary
cord is ye1 aeen.

From our observations on a fourth em-
bryo, of 11 centimetres [4$ inches |, sa\

152 THE ORIGIN AND FORMATION

of twelve weeks, we ascertained that at
this period the follicular walls are not-
closed, and that no trace of the dentine-
cap is yet visible. The next embryo
examined (measuring 15 centimetres [6-
inches], indicating thirteen weeks,) showed
no perceptible difference in development
as compared with the former.

In an embryo of 20 centimetres [8-
inches] (say at the commencement of the
fourth month) we collected some valuable
facts in regard to certain ulterior phases of
evolution.

At this epoch the primitive follicular
cord has not yet become severed, nor the
follicle closed. A little cap of dentine is
seen very clearly outlined in some, though,
not in all, of the follicles of the temporary
dentition. It is, in fact, at the exact period!
when a slight trace of ivory is formed that
we discovered the first chronological differ-
ence in the development of the follicles of
the temporary teeth. For while the inci-

OF THE DENTAL FOLLICLE. 153

sors and the canines are now pro\ ided with
a cap of embryonal dentine, it does noi ap-
pear upon the molars until about a week
later. The l>ull> [dentine-germ] has now
the exact form of the crown of the future
tooth; its base has already become con-
stricted and is embraced by the margins of
the enamel-organ, which is already com-
pletely constituted, with its internal layer
of cells [ameloblasts], and the stratum >n-
t< rmedium well defined.

It is also at this period <>f development
that we first sec, emanating from the primi-
tive cord, those buddings which are des-
tined to form the secondary cords, or the
enamel-organs of the permanent teeth. All
these bourgeons (or buds) representing the
commencenienl of the permanent follicles.
are, in both jaws, at the same stage of evo-
lution | in other words these enaniel-lmds
stall simultaneously ].

From an embryo of nearly the same di-
mensions as the preceding (23^ centimetres
11

154 THE ORIGIN AND FORMATION

[9£ inches] in length, and corresponding to
the eighteenth or nineteenth week), we have
fixed the epoch at which the separation of
the secondary cord from that of the primi-
tive follicle takes place. The latter now
becomes isolated from the epithelial lamina
and continues its evolution without any
further connection with this tissue. (Fig.
31, p. 133.) The permanent follicle, how-
ever, still remains attached to the cord, and,
by the lajbter, to the epithelium. We direct
attention to these facts, because in neglect-
ing to take account of the successive phases
of evolution one might be led to believe
that the follicles of the permanent teeth
originate directly from the epithelial lamina,
and not from the cords of the temporary
teeth. This last mode of genesis is, on the
contrary, definite and invariable for all the
follicles of the permanent teeth which have
been preceded by corresponding temporary
teeth, that is to say, for twenty of the teeth
of the second dentition; viz., the eight in-

OF Tin: iiknta L FOLLI4 LE. 1 55

cisors, tlic four (•.•mine-- and the eight pre-
molars [bicuspids]. It will be seen thai
the other follicles of the permanent teeth
have a diiferenl origin. The sections taken
from the jaws df the embryo ( l'" centi-
metres in Length) have enabled us t<> deter-
mine positively tin- period and tin- mode <»f
genesis <>f the cord of the first permanent
molar, which is not. as is known, preceded
by a corresponding temporary tooth. This
genesis takes place at the extremity of the
epithelial lamina; and since, in the embiyo
above named, the epithelial cord had al-
ready acquired considerable length, we
may reasonably conclude that its develop-
ment commenced about the seventeenth
week of gestation. (Fig. 39, ISumma/ry.)

At this epoch, when the separation of
the temporary follicles from the cord of the
corresponding permanent ones takes place,
there appears also the firsl trace of those
phenomena of buddings and of divers pro-
liferations of the debris of this primitive

156 THE ORIGIN AND FORMATION

cord and of the epithelial masses on the
walls, — particularities which were first de-
scribed in France.* By the examination of
other human embryos ranging from 27 to
37 centimetres [lOf to 15 inches], and up-
ward, we have been able to fix the subse-
quent phases of evolution, not only of the
temporary follicles, but also those of the
permanent teeth. These successive studies
have thus brought us up to, and even be-
yond, the period of birth. In this manner
we have been enabled to establish two
points which remained to be elucidated in
this order of researches, namely : the mode
and epoch of the evolution of the follicles
of the second and third permanent molars.
The results to which we have arrived in
regard to these, are the following : On ex-
amining sections taken from the jaws of
subjects two or three months after birth,
we discover in the region occupied by the
follicle of the first permanent molar, a pro-

* See Robin et Magitot, loc. cit., p. 75.

OF THE DENTAL FOLLICLE. I •) i

vc>< or prolongation, cylindrical in form,
emanating from the epithelial cord of the
latter follicle, and which takes a horizontal
and backward direction, terminating in a
bullions extremity. This prolongation is
the commencement of the follicle of the
second permanent molar. Thus we fix the
date of the origin of this follicle at the
third month after birth. At about the
third year of infancy the epithelial bour-
geon that represents the enamel-organ of
the third molar originates from the cord of
the preceding tooth, that is, the second per-
niaiicnt molar. According to the numerous
observations we have made, this date may
lie regarded as very nearly accurate, though
tin' difficulties of which we have already
spoken have prevented us from following
out the successive phases of evolution in a
very rigid manner. Yet that a little cap
of dentine is visible in this follicle about
the twelfth year. is true beyond a doubt.
Without continuing further the long

158 THE ORIGIN AND FORMATION

analysis of the many anatomical prepara-
tions we have made, we will present a sum-'
mary of them all in a tabular form. In
this are indicated the age and size of vari-
ous embryos corresponding with the suc-
cessive phases of follicular evolution. This
table is the first which has yet appeared
giving these in such a complete and exact
manner.

An examination of this table enables one
to see at a glance the different phases of
dental evolution in man. The indications
which it furnishes are founded on the ex-
amination of a considerable number of sec-
tions ; and consequently they appear to us
to show great accuracy. Aside from their
physiological interest, they not only have
an important bearing upon the complex
teratology of the dental system, but are
especially valuable in a surgical point of
view. There will be found, in fact, some
valuable data concerning certain anomalies,
whether in the position, direction, or in the

OF THE DENTAL FOLLICLE. 159

different arrangements of the dental system.
Besides they throw Ligh.1 upon the pathog-
ony of certain follicular cysts and help to
fix the period at which these pathological
productions make their appearance, as well
as thai of certain derangements of nutri-

■

tion, — the odontomes, for example. We
believe, then, that it will be found service-
able in certain cases in practice.

The results of the observations we have
made -on other species of mammals have
been less conclusive; sometimes on account
of the head only being placed at our dis-
posal, and sometimes owing to the change
of size and form that they have experienced
bj prolonged maceration; and finally in
consequence of the absence of all statistics
establishing the coiTespondence between
the age and length of the animal. Cer-
tain of them have, however, enabled us to
gather some useful data which we will
here present.

160

THE ORIGIN AND FORMATION

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OF THE DENTAL FOLLICLE. 1 6 1

Iii the canine species our observations
have been limited to the examination of a
lew Dew-bora puppies; accordingly the
Pacts concerning the chronology of the
dental follicle in this animal are very few.
We have, however, ascertained, that at the
period of birth, the follicles of the first
dentition are already provided with a cap
of dentine; that the cord of the permanent
incisors has made its appearance, and that
in l he centrals we can already discern the
first traces of the dental bulbs. In the
ovine and bovine species our studies have
extended to a large Dumber of embryos, but
owing to the absence of information we
have not been able to determine their exact
ages. We proceed, however, to give some
of our observations, taking into considera-
tion simply the length of the animals ex-
amined. In an ovine embryo of 4l} milli-
metres | about 1 v inches] in length (Figs,
16 and 1 (.), Summary of Flhts.} we find
on the edge of the jaws only the bourrelet,

162 THE ORIGIN AND FORMATION

or projecting band, with no trace of the
epithelial lamina. But when the embryo
has attained 52 millimetres [2 inches] we
perceive the epithelial lamina well devel-
oped. (Figs. 17 and 18, Summary of lllus.)
In an embryo of 65 millimetres no addi-
tional change is percejrtible in the develop-
ment ; yet with a magnifying power of about
300 diameters one can study in this the con-
stituent elements of the lamina. (Fig. 18,
Summary of -Illus.)

When the embryo has attained 72 mil-
limetres [about 3 inches] the extremity of
the lamina shows a very marked enlarge-
ment, which represents the enamel-organ of
the future tooth. (Fig 21, Gr, Summary?)

Ajb a little more advanced period, in an
embryo measuring 82 millimetres [31
inches], the enamel-organ and the dentine-
bulb have completed their formation, and
the follicular wall has made its appearance
at the base of the bulb. (Figs. 26 and 28,
Summary?)

OF THE DENTAL FOLLICLE. I 63

When the embryo has attained 1 1 \ cen-
timetres 1 4.1 inches] we observe thai the
walls arc completed, ami closed around the
epithelial cord which is about to be rup-
tured. At this period, also, we discover
the first appearance of the dentinecap.
Such arc the tacts wc have collected from
the embryonal Lambs which we have been
able to procure.

In the bovine embryo our observation-,
in a chronological point of view, have been
much more limited, the head- only of these
embryos having been placed at our dis-
posal, without any information as to the
period of gestation. These specimens, how-
ever, have enabled us to furnish some de-
scriptive details which are very distinctly
shown in this animal. ( Pigs. 38, 41 and 42,
Summary.) We will state, however, that in
a foetus of eighl months we have found the
temporary incisor teeth quite fully devel
oped, the follicle of the permanent incisors
complete, ami the dentine-cap beginning to
form.

164 THE ORIGIN AND FORMATION

Our observations have been made upon
equine embryos of different ages. From
these we have determined certain facts in
relation to the various phases of follicular
evolution. For the first three embryos we
are indebted to the courtesy of M. Raynal,
of the veterinary school at Alfort. In the
youngest of these (14 weeks) the enamel-
organ of the central nippers (incisors) are
already formed, and the bulb has made its
appearance. For the lateral nippers the
enamel-organ is just beginning to show it-
self. These facts indicate that the evolu-
tion of the follicles varies in point of time in
the different incisors; whereas the evolu-
tion of the follicles of these teeth in man
and other mammals appeal's to be synchro-
nous. For the molars, it is found that at
this same epoch the bulb has appeared for
all the follicles of the first dentition, as have
also the first traces of the follicular wall.

In a second embryo (of 27 weeks) the
follicles of the central incisors are closed,

OF THE DENTAL FOLLICLE. 165

while those of the firsi lateral incisors are
jusl beginning to exhibit the l>nll>s; and
those of the second lateral incisors only the
enamel-organ. These facts, as we see, ad-
ditionally confirm the unequal development
of the different incisors in this animal. In
the molars the facts are analogous; the fol-
licle of the first temporary molar is closed
at this date, while the enamel-organ of the
second lias only just made its appearance,
and no trace of that of the third molar is yet
visible. It is at this period, also, that the
first indication of the enamel-organ appears
for the first permanent molar.

In a third embryo, measuring 255 mil-
limetres [10 inches |, corresponding to about
28.1 weeks, the follicles of the permanent in-
cisors are closed and complete; the enamel-
organ is well developed. The ameloblasts
of the interior bed are verj large, and the
external epithelial layer has already disap-
peared,* bul no t race of dentine yet appears.

* [The above statement, concerning the early disappear-
ance of the external epithelial layer of the enamel-organ, is

1(t6 ♦ THE ORIGIN AND FORMATION

The follicles of the permanent incisors
have arrived at the period when the enamel-
organ already caps the bulb, which is just
appearing, but is not yet constricted at its
base. (Fig. 29, K, Summary.} For the tem-
porary molars the follicles are about equal-
ly developed. They are closed and well
formed, but without any appearance of the
dentine-cap. The organ of coronal cement
is already beginning to manifest itself.
From the fragments of the ruptured epi-
thelial cord numerous buddings have been
produced.

From the fourth (an equine foetus of 31^
weeks), owing to a very prolonged macera-
tion in alcohol, we were prevented from de-
riving much advantage. We were only
able to determine that the temporary folli-
cles were fully developed and provided with
caps of dentine of considerable thickness.
Some fragments of the epithelial cord (long
since broken, without doubt,) were still re-

evi den tly erroneous ; the sections examined which led to this
opinion were probably defective. — Tr.] *

OF THE DENTAL FOLLICLE. 1 <»7

maining. The organ of corona] cement was
fully developed.

We will conclude these chronological con-
siderations with a few notes relative t<» the
rodents: In an embryonal guinea-pig of 2
centimetres | J inch] in total Length, which
appeared to correspond to about the middle
period of gestation, the follicle was at the
stage when the enamel-organ, in form of a
hood, covers the bulb; there was no follicu-
lar wall or dentine-cap apparent.

In another embryo of the same species,
of 4 centimetres | 1 1 inches] in length, the
temporary follicles were formed, and their
stages of development were nearly the same.
They were provided with a dentine-cap,
covered with a thin layer of enamel. In the
rabbit we discover that, at birth, the incisors
have effected their eruption, the molar- -till
enclosed, but already capped with thick
layer- of dentine and enamel. Beneath the
temporary molars we observe the presence
of the permanent follicles, already provided

168 THE ORIGIN AND FORMATION

with a thin but distinctly manifest layer of
dentine.

We will not pursue these considerations
further, which are of less interest in the
lower mammals than in man, in regard to
whom we have presented a large number
of examples.

OF THE DENTAL FOLLICLE. 1 0'.»

CHAPTER VII.

CBITICISM OF THEORIES l.'IM Ml". VXD CONi USIONS.

npiIK problem of the genesis and forma-
-*- tion of the dental follicle in mammals

has, for a loni: time, l>een the subject of
numerous researches, and lias given rise t<>
many theories. The relatively early period
in embryonic lite at which these phenomena
commence; the difficulties attending the
preparation of the specimens (the treat-
ment by different reagents to which they
must be submitted, etc.), are so many causes

which have retarded the progress of exact

knowledge regarding the embryogenic evo-
lution of these organs. The question has
passed through numerous phases, and, with-
out going l>aek very far in its history, and
without presenting the opinions of ancienl
authors, imbued with preconceived notions

12

170 THE ORIGIN AND FORMATION

of the nature of the teeth, or strangers to
the processes of investigation of the modern
anatomical -school, we will say that in going
back no farther than the middle of the last
century we find that Herissant* having con-
ceived that he found on the surface of the
mucous membrane of the gums certain small
depressions, considered them to be orifices
of canals communicating with the dental
follicles. This opinion, which rested on no
anatomical fact, was adopted by only a
few authors (Bonn, 1773; Oudet, 1835).
According to the theory of Herissant,
which we find at a later day more clearly
presented by Groodsir, the mucous mem-
brane of the gums would be the point of
origin of the follicle, the wall of which
would be developed before the follicle it-
self. In 1835,f in an important work,

* Nouvelles recherches sur la formation de V email des
dents et sur celle des gencives. Mem. de VAcad. Paris,
1754.

f Meletemata circa dentium mammalium evolutione Vratis-
larice. In. 4°, 1835, p. 12.

OF THE DENTAL FOLLK LE. 171

Rasdikow advanced tin- theory that the
dental follicle is produced al the inner face
of the mucous membrane, without the- nec-
essary participation of the latter; however,
he does not specify which of the organs of
the follicle appeals first, nor how the others
are produced. Nevertheless, Henle,* Bis-
choff,f and KollikerJ (in the first edition
of his microscopical anatomy) support his
opinion. A few years later appeared the
work of Goodsir,§ in which is formulated
that well-known theory according to which
both the temporary and the permanent fol-
licles originate directly from the mucous
membrane itself. Immediately adopted,
without verification by the majority of au-
thors, it is even now nearly the only theory
found in the greater number of treatises on

*Anat. i/i'ii. 1845, p. Hi <t suiv.

t TraiU du developpement, 1845, p. 401-418.

\Mikro8cop. Aunt.. 1856, traduction franchise dt beclard
< i Se\ . p. 490.

£ On tin- origin and development oj thi pulp and sacs of
the human teeth. Edinburgh " Medical and Surgical Jour-
nal," 1838.

172 THE ORIGIN AND FORMATION

anatomy and physiology. We will not
describe here this theory, according to which
the follicles of the two dentitions result
from a simple introversion of the mucous
membrane ; it is founded on no anatomical
fact, unless it be the formation of a groove
which is produced on the alveolar border
of the embryo by a prolonged maceration
of the preparations, thus effecting the sepa-
ration of the epidermic bed, which forms
the epithelial band, from the groove which
incloses it. It is, then, as we have said,
solely by an artificial process, as Kolliker*
and Kollmann f have already remarked,
that the theory in question can have any
appearance of reality; for nothing in the
normal condition of the jaws can be found
to lend support to it in any way. Not-
withstanding the success of Groodsir's the-
ory, universally accepted in England and
Germany, N. Guillot published in France

*Histologique humaine. Edit. Trad. fran<?aise, 1869.
f Loc. cit., p. 150.

OF THE l>i via I. FOLLICLE. I To

a work* in which he endeavored t<> show
thai the teeth are developed without the
slightest participation of the mucous mem-
brane; that it is from a mass originating in
tlic depth of the embryonal tissue that the
follicle is produced. This mass he calls
the i nit ml spheroid, or primitive trace of
the tooth, lie describes in this " spheroid "
thre<' divisions: a central one. which he
names the nnch-ns. representing' the bulb ,'
an intermediate one surrounding the other,
the < ma/niel-orga/n ; and lastly, the external
one, which will become organized to form a
membrane, he calls the dental sac. From
this description, as a whole, it is easy to see
that N. Gruillot has limited himself to the
examination and figuring of sections made
through follicles which are in an advanced
stage of evolution, and that he has not hit
upon the mode of origin of the component
parts <>f the organ and their successive

* Recherche* sur In genise >-t V evolution dee dents ft des

Mdchoirea. Ann. des 8C. nut., IV" sc'rii', t. IX, 1858.

174 THE ORIGIN AND FORMATION

phases of development. This work, then,
has thrown no light upon the question.

Several years later (in 1860) appeared
in France an extended work, published by
M. Ch. Robin, in connection with one of
the authors of this work.* This memoir
contained a complete theory of follicular
evolution, according to which the dental
bulb is the first part of the follicle that
appears in the depth of the jaws, at the
bottom of the groove and in the vicinity of
the principal vessels and nerves ; afterward
the enamel-organ is seen ; and then the wall
emanating from the bulb, and rising upon
the sides of these organs so as to surround
them and to unite at the apex of the folli-
cle. Whatever may be the accuracy of the
descriptions in this work, it is evident that
its authors misconceived the true order of
the genesis of the follicle ; for in reality the
enamel-organ makes its appearance before
the bulb.

* Robin et Magitot, M6tnoire cit<5 Journal de physiologie
de Brown-Sequard, 1860-61.

OF THE DENTAL FOLLICLE. 1 75

Whence comes this error in the interpre-
tation of the very first phenomena of folli-
cular evolution? It results evidently from
the too exclusive mode of examination
which was adopted; for the observations
were made upon preparations of follicles
gradually flattened between two plates of
glass. Very few sections were made. The
authors wished thereby to preserve, in their
reciprocal relations all the parts which they
dissected, for the purpose of further re-
searches in detail. The fear of deforming
the sections and disturbing the relations
which sometimes result from cuttings made
upon masses of tissues somewhat thick,
and we must say the insufficiency of the
processes of hardening known at that
period, — all these combined singularly to
Lead these anatomists into the error that
they have there committed.

The question was at this point, wheo
Kolliker discovered (1863*) the existence

* Die Enttoicklung der Zahnsdckchen der Wiederk&uer.

Zeitschr. f. Wissen. Zool. 18G3. Gewebelehre, 4 Aufl.

176 THE ORIGIN AND FORMATION

of an epithelial band subjacent to the gin-
gival ridge of the mucous membrane, and
which extends the entire length of the
jaws. This continuous lamina Kolliker
calls the enamel-organ; but we regard it
only as a simple dependence of the epithe-
lial band. The term enamel-organ does not
appear to us to be appropriate to a lamina
which does not contribute directly to the
formation of the follicle, since it is upon a
certain number of points of this that bour-
geons appear, from which the enamel-organs
are directly developed. These bourgeons
are in number equal to that of the future
teeth; and in the intervals between the
bourgeons, or enamel-organs, the epithelial
lamina remains unchanged.

Whatever may be said of the interpreta-
tion of them, the views of Kolliker are very
just ; and they became the starting-point of
a series of observations which gave to the
question of the evolution of the dental fol-
licle an entirely new aspect. Two facts

OF THE DENTAL FOLLICLE. 177

were from that time settled, namely, that
the enamel-organ appears as the firsl con-
stituent part of the follicle, and that its
origin is epithelial. Upon this last poinl
tin- views previously pur forth by Marcuses
and Huxley were continued." Following
the work of Kolliker are grouped a consid-
erable number of researches emanating from
his pupils, or coining from other German
schools. Such are the memoires of Wal-
deyer, Hertz, Wendzel, Kollmann, etc. f

* Marcusen, Ueber die Entwicklung der Z&hne. Bulletin
de VAcad. imperiale de Saint Petersbourg, 1849. Huxley,
Quint. Journal of Microscopical Science, 1854, 1855. 1857.

fWaldeyer, Untersuch. uber die Entwicklung der Z&hne:
I Abth. Konigsberg und Jahrbttcher IV. Bd. 1864; II Abth.
Zeitschr. fur rat. Med.; Ill, 24 Bd. 1865.— IV. Bau und
Entwicklung der Z&hne in Strieker, Handbuch der Lehre
ton den Gewehen. Leipzig, 1871, p. 333 et Buiv.— Hertz,
Untersuchungen uberfeineren Ban und die Entwicklung der
Z&hne. Virch. Arch. 1866, Bd. 37; id., Kin Full von
geheiUer Zahnfractur mit nachfolgender Schnielzbildunff.
Virch. Arch. 1806. 2* Bd. — Wendzel, Untersuchungen fiber
das Schtnehorgan und den Schnieh. etc. Arch, von ILkde.
1868, p. 97.— Kollmann, Entwicklung der Milch und Ersatz-
z&hne beim Menschen. Zeitschrifl fur Wissenschaftliche
Zoologie, von Seibold und KSlliker; Zwanzigster Baud.
Zweitea Heft. p. 145. Leipzig, 1870.

178 THE ORIGIN AND FORMATION

In these different works the idea of
Kolliker is taken at the initial point. Wal-
deyer described exactly the descent of the
cord, and the formation of the component
parts of the follicle. He indicates, also, that
the follicles of the permanent teeth arise
from buddings from the primitive cords;
but he fails to mention, in regard to them,
the different modes of genesis, and also the
precise points where this genesis takes place.
He points out, moreover, in his last publica-
tion,* the unsettled difficulties which exist
in these questions, notwithstanding the nu-
merous works published upon this subject.
Hertz and Wendel support the opinions
promulgated by Kolliker and Waldeyer,
without adding anything new to the ques-
tion of the origin of the follicle. They
have, however, advanced some new ideas
upon other points of follicular evolution,
which we will discuss on another occasion.
As to Kollmann, the last German anato-

*See in Strieker, loc. cit. 1871, p. 352 (English Edition).

01 I Hi: DENTAL I oi.i.it 1.1 . 1 79

mist who has studied the question, lit- adopts
unhesitatingly the views of Kolliker ;m<l
Waldeyer od the subjeci of the origin of
the enamel-organ of the temporary teeth;
but in regard to the origin of the perma-
nent follicle, sometimes he derives it direct-
ly from the mucous membrane, sometimes
from the epithelial debris of the primitive
cord, and at others from an epidermic glob-
ule. It is also from one of these last that
he makes the supernumerary follicles arise,
as we have already mentioned."" The Ger-
man authors are, then, very far from agree-
ing:, ^ls we S(J<", in regard to the mode of
origin of the dental follicle. As to the
phenomena which take place within that
organ after the origin of the bulb, and the
formation of the wall, and the transforma-
tion of the enamel-organ, they are <\\\ in
controversy. In our opinion, and we may
thus in a few word- resume our work, the
formation of the dental follicle consists, es-

* [See p. 66 of this work— Tk.]

180 THE ORIGIN AND FORMATION

sentially, in the genesis of two organs, one
of which is of an epithelial nature, ema-
nating from the epithelium of the mucous
membrane, the other of an embryoplastic
nature, originatino; m the midst of the em-
bryonic tissue of the jaws. The first of
these is the enamel-organ, the second is the
bulb, or dentine-organ ; thus they are formed
individually and then proceed to meet each
other. The enamel-organ becomes in a man-
ner the cap of the bulb, while from the
base of the latter emanate membranous
processes, which envelop little by little the
two organs, and at last entirely close the
follicle. If one examines the origin and
growth of these organs from the point of
view of general physiology, he is immedi-
ately struck with the extreme analogy they
present to the phenomena of the formation
of the hair-follicles. In the latter, as well
as in the former, one sees on the one hand
an epithelial cord which descends from the
Malpighian layer into the dermis ; then on a

OF THE DENTAL FOLLICLE. 181

point of the latter appears the bulb, which
penetrates the former, ami makes of it a
Cap for itself; while from its base emanate
those processes which are to form the walls
of the follicle. These facts show the close
analogy of these two organs. (Fig. 40.)

Thus we mid confirmed, by actual physi-
ological ami embryological facts, the theory
enunciated a Long time since by De Blain-
ville, regarding the analogy in the compo-
sition and formation of the plianeres, as well
as the doctrine of the j>/-o<///rfs developed
with so much precision in the modern ana-
tomical school of Ch. Robin.

CONCLUSIONS.

1st. The dental follicles first appear as a
cord emanating from the epithelial layer of
the oral mucous membrane.

2d. The cords that give origin to the fol-
licles of the first dentition arise directly
from a process of the oral epithelium (epi-

182 THE OEIGIN AND FORMATION

thelial band and epithelial lamina). The
cords for those permanent teeth which .suc-
ceed the temporary ones are diverticula or
outgrowths from the primitive cords. As
for the cords of the other permanent teeth,
those for the first molars originate directly
from the epithelium of the mucous mem-
brane, and the remaining ones (eight in
number) from the cords of the preceding
molars. (See table.)

3d. The cord, whatever may be its point
of origin, is invariably epithelial ; it is com-
posed outwardly of a layer of prismatic
elements of the Malpighian stratum, and in
the interior, of polyhedric epithelial cells.

4th. The extremity of the cord, which
soon takes the form of a club-shaped swell-
ing, constitutes the enamel-organ of the
future follicle.

5th. The dental bulb apj3ears spontane-
ously in the midst of the embryonic tissue
and at a point in immediate proximity to
the deeper face of the enamel-organ.

OF THE DENTAL FOLLICLE. Is"'

6th. The enamel-organ covers the bulb,
serving as a cap for it; an arrangement
which continues during all the periods of
evolution, preceding the formation of the
dentine and the enamel.

7th. The follicular processes emanate
directly from the elements of the bulb, and
rise from its base to the summit of the fol-
licle, where they unite and constitute the
follicular sac.

8th. Synchronous with the closing of the
follicles is the rupture of the cord; and
from this period the follicle loses all con-
nection with the epithelium of the mucous
meml irane. The formation of the follicle is
now complete.

9th. The evolutionary phenomena of the
follicles in both dentitions are identical as
to their nature; the only perceptible differ-
ences are in regard to the exact point from
which the epithelial cords originate, and
the length of time necessary to accomplish
their successive phases of evolution.

184 THE DENTAL FOLLICLE.

10th. The mode of evolution of the den-
tal follicle and of the pileous follicle is
identical.

Frank : Are, then, our readings to terminate
here ?

Teacher : The appearance of the second me-
moir in the series has been long delayed, owing
to the death of one of its authors, the lamented
Dr. Ch. Legros. Much of the materials for this,
I am informed, had been collected before his
decease ; but the preoccupation of Dr. Magitot
has prevented his completing it up to the pres-
ent time. I am, however, daily expecting the
arrival of this treatise, and, should it be found
desirable, we may resume our readings.

If you have obtained a clear idea of the phe-
nomena of the origin and growth of the dental
follicle from the present work, you have acquired
far more than has been hitherto taught in any
of our medical or dental schools, or can be found
in any other publication upon this subject ; and
though it will, doubtless, become necessary for
you to modify your views in some particulars, as
this branch of science progresses, yet the knowl-
edge you have here gained will enable you to
readily perceive and appreciate the value of
future researches made either by yourselves or
by other observers in this field of study.

SUMMARY OK ILLUSTRATIONS

AND A BRIEF

DESCRIPTIVE REVIEW.

All figures not accredited to other sources are copied
from the original work.

The dental bulbs, in some of the following figures, pre-
sent a vascular appearance, not seen in those from which
they are copied. It was believed that by thus representing
them, the student might more readily recognize the diff-
erent parts of the developing follicle.

13

186 SUMMARY.

Fig. 1. — This diagram shows the relative position of the
different layers which are designated the mucous, or "prop-
er " mucous, membrane by various writers. The column on
the left gives the names and location of the strata of the
mucous membrane as we think they should be designated.
The horizontal lines show the relative location of these lay-
ers, without any regard to their thickness. M. S. D., del.
(See p. 11.)

Fig. 2. — This cut was designed to illustrate the cells of
the epidermis E,m some of their various phases, as de-
scribed (p. 18 et seq.) a, Stratum corneum; b, stratum Mal-
pighii, with its prismatic or columnar layer resting upon the
basement membrane, b m; c, upper portion of the dermis.
The papillae are not represented in this figure, nor the sub-
dermal layer. M. S. D., del. (See p. 18 et seq.)

Fig. 3. — The so-called "spinous," "ridged," "imbri-
cated," " aculeated," " prickle " or " heckle " cells. Frey.
(See p. 50.)

Fig. 4. — Showing the lowest layer of the Malpighian
stratum (a); the intermediate matter (&); the basement
membrane (c); and the fibrous tissue of the dermis {d).
(From Frey. Diagrammatic.) Though the cells of this
layer always stand nearly perpendicularly, their form is
varied; for example, the basal extremities are truncated in
the ameloblasts, somewhat like those seen in Fig. 7, p. 191.
(See p. 21.)

Fig. 5. — Stellate cells, such as compose the "stellate
reticulum" of the enamel-organ. Diagrammatic, from
Frey. (See p. 77.)

Fig. 6. — Cut to represent the basal aspect of a layer of
ameloblasts; showing their prismatic or hexagonal form.
M. S. D., del. (See p. 85.)

I'm.. 1.

1-1 Class. 2d Class. 8d Class. 1th Class.

BO

a

t
2
a
H

Strat. corn.

Mi

Stral Malp.

•M. nierab.

-

z

-

Basement memb.

M. memb.

Dermis-* ;■"-''•■"'■
| Pars ret.

M. memb.

3

-
=

Subdermis.

—

Fig. 2.

Pis. 3.

Pig. 5.

ppsr^

Fie. i.

Pig. 6.

188 SUMMAET.

Fig. 9. — Meckel's cartilage ; from a human embryo of
forty to forty-two days. (Magnified 25 diam.)

a, Enlargement of cartilage near the neck of the malleus;
b, the mental symphysis where the two homologous parts
unite; m, head of the malleus; n, handle of the same; e,
cartilage of the incus; o, that of the os lenticulare; I, that
of the stapes. One side of the jaw has been outlined to
show the relative position it will occupy when ossification
takes place. (For further description of this and following
figures, see p. 32 et seq.) Magitot and Robin.

Fig. 10. — Cranium of a human foetus of four months;
natural size; showing .the membrane of the tympanum,
with the cartilages of the incus and malleus (&); also the
extra-tympanic portion of Meckel's cartilage (a). Magitot
and Robin.

Fig. 11. — Right inferior maxilla of a human embryo of
about three months; natural size. Soft parts removed from
the internal face, showing relative position of Meckel's carti-
lage, a, Extra- tympanic portion; b, symphysis; n, manu-
brium mallei (handle of hammer); e, incus (or anvil). Magi-
tot and Robin.

Fig. 12. — From a human embryo of about sixty days;
natural size. Soft parts removed, showing Meckel's carti-
lage and lingual face of the jaw-bone, left side. In this the
cartilage has much the appearance of a very large bristle.
A, Extra- tympanic part; b, symphysis; n, malleus. M . S. D.,
del.

Fig. 13. — From a foetus of four months; showing the
palatal aspect of the inter-maxillary bones. M. S. D., del.
(See p. 40.)

Fig. 9.

Fig. 11.

Fig. 10.

Pig. 12.

r

Ki<;. 13.

190 SUMMARY.

Fig. 14. — Vertical section of the anterior part of the face
of a human embryo of about 45 days, measuring 3 cen-
timetres [1% ml- (Magnified 80 diam.)

a, a, Meckel's cartilage; b, first trace of the submax.
glands; c, depression of the mucous membrane; a", epi-
thelial band, bourrelet of the lower jaw (see description, p.
51 et seq.)-. d, epithelial band of upper jaw; E, section of
the tongue; F, F, F, F, oral cavity, a thin bed of epitheli-
um clothes its surface; g, upper jaw; H, H, incisive (or in-
termaxillary) bourgeons, which have already united at the
median line.

This central line does not appear in the original figure,
and should terminate where it enters the lighter part. (See
description, p. 149.)

Fig. 15. — Embryo of 40 days, showing the mouth and
palatal region. (Coste).

1, First appearance of the nose; 2, 2, alse of the nose; 3,
closure of the incisive processes; 4, median portion of upper
lip, formed by the approach and union of the two. incisive (or
intermaxillary) processes, the little notch in the median
line still indicating the primitive separation of the two
processes. (See p. 29.)

Fig. 7. — Taken from Kolliker's Manual of Hist., showing
"a simple papilla [of the mucous membrane], with mani-
fold vessels and epithelium, from the gums of an infant.
(Magnified 250 diam.)" It is given here principally to show
the cells of the epidermis. (See p. 26.)

Kh. 14.

Kii.. 15.

Fig. :.

S

192 SUMMARY.

Fig. 16. — Vertical section taken from the incisive region
of an ovine embryo, 42 millimetres [1% inches] in length.
(Magnified 80 diam.) a, Meckel's cartilage; c, depression
of mucous membrane; d, epithelial band. The close prox-
imity of the parts of the severed cartilage shows the cut to
have been taken from the anterior portion of the jaw. (See
p. 53.)

Fig. 17. — Vertical section of the anterior portion of the
lower jaw of a,n ovine embryo, 59 millimetres [about 2 inches]
in length. E, E, epithelial lamina, emanating from the epi-
thelial band. The letters a, c, d refer to the same parts as
in the preceding figure. (See p. 63.)

Fig. 18. — Vertical transverse section of the left branch of
the lower jaw of an ovine embryo, 65 millimetres. (Magnified
260 diam .) This and Fig . 17 show the arrangement of the ele-
ments of the epithelial band, and also the epithelial lamina.
d, Epithelium of the mucous membrane, extending nearly
vertically into the embryonal tissue and constituting the
epithelial band, and the lateral process or epithelial lamina.

E, Epithelial lamina, emanating from the band. The band
and lamina are surrounded by the embryonal tissue of the
jaw. This portion of the engraving is faulty, in that the
nuclear elements appear lighter, whereas they should be
darker, than the surrounding mass. (See p. 63 et seq.)

Fig. 19. — From a porcine embryo (copied from Frey).
d, Mass of epithelium, — the "dental ridge,1' "maxillary
rampart " or " kieferwall ": b, younger layer of epithelium;
c, deepest layer, — the columnar or prismatic stratum; e,
enamel-organ. (See p. 52.)

Fid. 16,

Kio. IT. a

c

Fie 1!).

a e

Fig. IS.

'

194

SUMMARY.

Fig. 20.— Section from an embryonic lamb a little older
than that from which Fig-. 18 was taken; showing the
epithelial lamina. (Magnified 350 diam.) c, Prismatic or
columnar cells,— a continuation of the lowest layer of the
Malpighian stratum; d, large polygonal cells of the epi-
thelial band (bourrelet); E, smaller polygonal cells of the
epithelial lamina. The lamina now presents an enlarged
extremity, and this is the rudiment of the enamel-oman
(See p. 69.)

Fig. 21.— From the lower jaw of an ovine embryo (left
side), measuring 72 millimetres [2£ inches]. (Magnified 80
diam.) d and E same as in preceding figures; g, rudi-
mental enamel-organ. (See p. 70.)

Fig. 23.— From a bovine embryo (Wedl). d, Epithelial
band ("dental ridge"); b, enamel-organ ("follicular pro-
cess"); c, epithelium of the margin of the under lip, with
rudimentary hair-follicles. (Magnified 15 diam.)

Fig. 24.— From the incisive region of an ovine embryo,
lower jaw, 115 millimetres [4| inches]. (Magnified 80 diam.)
a, Meckel's cartilage; b. osseous trabecular; c, c, dental
artery; d, epithelial band; E, epithelial lamina; /, cord; g,
enamel-organ; H, rudimentary bulb. •

In this figure, which has been drawn from nature, as well
as all the others, certain defects, which have resulted from
too long maceration, have been preserved in the drawings;,
hence the space seen between the follicular wall (I) and the
enamel-organ (g) is artificial, and does not appear in fresh
preparations. It will be seen, on the right side of the figure,
that the cut was not in line with the follicle, and that only
the lamina is apparent.

g E

Pig. 22.

'■' -

Pig. 28.

rf A

j --«;-. i '-'

Fig. 24.

196 SUMMARY.

Fig-. 25. — From lower jaw of an equine embryo, 190 milli-
metres [7f inches] in length. (Magnified 80 cliam.)

a, Meckel's cartilage; b, traces of ossification; E, epi-
thelial lamina; F, cord; g, enamel-organ; H, bulb; I,
follicular wall. This figure shows the same defect alluded
to in Fig. 24.

Fig. 26. — From lower jaw of an ovine embryo, 82 milli-
metres [3£ inches] in length. (Magnified 80 diam.)

a, Meckel's cartilage; E, epithelial lamina; F, epithelial
cord; g, enamel-organ; H, bulb; I, follicular wall; K, second-
ary bourgeon, from which the enamel-organ of the per-
manent tooth originates.

Fig. 27. — From lower jaw of a bovine embryo, magnified
80 diameters.

a, (in the center of the figure), Meckel's cartilage; b,
traces of ossification; d, oral epithelium; E, epithelial lam-
ina; F, epithelial cord; g, enamel-organ; H, dental bulb;
I, ''internal epithelium," or layer of ameloblasts; /', ex-
ternal epithelium of the enamel-organ ; K, secondary enamel-
bourgeon.

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198

SUMMARY.

Fig. 8.— Ideal dental follicle, before the rupture of its
cord. Drawn solely to show the position of the basement
membrane, and the ^reformative membranes of Raschkow
and Huxley. (For full description, see p. 89.)

BM, basement membrane; N, neck; S, sac or follicular
wall; 0, enamel-organ; B, bulb; E E, external epithelium
of the enamel-organ and the basement membrane; E C
epithelial cord; C T, connective tissue surrounding the
enamel-organ; E p, epidermis or oral epithelium.

The parts embraced between the points where the di-
vergent lines A A terminate are: (1) the concave face of
the enamel-organ, lined with a layer of ameloblasts, or the
"internal epithelium"; (2) the membrana praformativa of
Huxley, or the tissue composed of the basal coverings of the
ameloblasts; (3) the membrana prseformativa of Raschkow,
or the basement membrane; (4) the dentine-bulb itself.—
(Diagrammatic.) M. S. D., del.

Fig. 28.— Section through the incisive portion of the
lower jaw of an ovine embryo, measuring 82 millim. [3%
inches] in length. (Magnified 260 diam.)

d, Oral epithelium; c, lowest layer of cells in the stratum
Malpighii; F, epithelial cord; -ST, bourgeon of the secondary
cord; I, follicular wall; H, dental bulb. (See p. 162- also
Fig. 26.)

Fig. 29.— Vertical section of the anterior portion of the
lower jaw of an equine foetus, 255 millimetres [10£ inches]
in length, and corresponding to about 28^ weeks. (Mag-
nified 80 diam.)

a, Meckel's cartilage; b, traces of ossification; d, oral
epithelium; g, enamel-organ; H, bulb: /, layer of amelo-
blasts; K, bulb of the permanent tooth, capped by the
enamel-organ, with some traces of the secondary cord; L,
place assigned for the development of the cement. (See
description, p. 165.)

Fio. 88

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200 SUMMARY.

Figs. 30 and 31. — These cuts are taken from the incisive
region of different human foetuses, evidently not far from the
sixteenth week of gestation. A detailed description of the
figures would be unnecessary. The cuts are introduced
here simply because they present one peculiarity that is not
represented in the other figures, viz, the origin of the epi-
thelial cords for the permanent incisors directly from the
epithelial lamina, instead of their being offshoots from the
cords of corresponding temporary follicles. These are desig-
nated by the letters E on the right of the figure.

Though these figures seem to establish the fact that the
teeth of replacement are sometimes derived directly from
the epithelial lamina, yet we must not regard these as con-
clusive evidence until they are fully verified by other skill-
ful histologists.

For the drawings of these 1 am indebted to my friend
Dr. Black. (See description, p. 137.)

Fig. 31. £ KU*,

202 SUMMARY.

Fig. 32. — "From the upper jaw of a kitten about the
time of birth.

a, Oral epithelium; b, bone of jaw; c, neck of enamel-
organ; d, dentine papilla; e, enamel-cells; /, stellate retic-
ulum; h, tooth-germ of the permanent tooth, the enamel-
organ of which is derived from the neck of its predeces-
sor."— From Tomes' Man. of Dent. Anat.

Fig. 33. — A cut through the follicle of a lower temp,
molar of a human foetus, 20 centimetres [8 inches] in length;
about the seventeenth week of gestation. (Magnified 80
diam.)

a, Meckel's cartilage; b, traces of ossification; c, c, dental
artery and nerve; d, epithelium ; E, enamel-organ; F, cord
of the temporary follicle; //, bulb; /, follicular wall; K,
cord of the permanent follicle. (See p. 152.)

Fig. 34. — Section of the lower jaw of a human foetus,
23% centimetres [91 inches] in length; corresponding to
about the eighteenth week. (Magnified 80 diam.)

K, Cord or bourgeon of the secondary follicle; L, point
where its separation from the primitive cord is being
effected; a, Meckel's cartilage diminished by absorption;
b, bone of the jaw; c, (upper) dental artery, (lower) dental
nerve; d, epithelium; E, originally the cord of the tem-
porary follicle, but now the sole property of the permanent
one. (See p. 153.)

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204 SUMMAKY.

Fig. 35. — Section on a line with the follicle of the first
permanent molar. Human subject, three months after
birth. (Magnified 80 diam.)

b, Maxillary bone; c, c, dental artery and nerve; E, cord
of the follicle of the first permanent molar; g, enamel-
organ; H, bulb of the first permanent molar; K, bourgeon
of the enamel-organ of the second permanent molar. (See
p. 156.)

Fig. 36. — Vertical section of the lower jaw of a human
foetus, measuring 47 centimetres [18% inches]; correspond-
ing to nearly the thirty-ninth week of gestation. The figure
represents a cut passing through the follicle of a bicuspid.

b, Bone of the jaw; d, oral epithelium; g, enamel-organ;
H, dental bulb; K, debris of the cord of a permanent fol-
licle; K' K', epidermal globules. Follicle for the perma-
nent tooth connected with the debris of its cord, K.

Fig. 37. — Vertical transverse section through the incisive
region of the lower jaw of a human foetus, measuring 38
centimetres [15i inches]. (Magnified 80 diam.)

b, Bony formation ; d, oral epithelium; g, enamel-organ;
H, dental bulb; J, cord of the permanent follicle; K, debris
on the follicular wall of the primitive follicle and from its
cord; K', epithelial globule; L, enamel-organ of the per-
manent tooth.

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Fig. 37.

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206 SUMMARY.

Fig. 38. — From the lower jaw of an ovine embryo, mag-
nified 80 diameters; showing the completed dental follicle
and the sun-ounding tissues.

a, Meckel's cartilage; b, traces of ossification; c, lowest
layer of the epithelial cells; d, oral epithelium; F, amelo-
blastic layer; F, (lower) external layer of the enamel-organ —
a continuation of the layer of ameloblasts; g, stellate retic-
ulum of the enamel-organ; H, bulb; 7, follicular wall; K,
buddings from the cord.

Fig. 39. — From a human embryo, 20 centimetres [8
inches] in length. (Magnified 80 diain. )

a, Meckel's cartilage; b, bone; c, c, artery and nerve;
d, oral epithelium; E, cord of the first permanent molar
originating from the lamina; F, debris of the cord of the
preceding follicle; g, muscular insertions. (See description,
p. 155).

Fig. 40. — A section of the skin of a human foetus, 20
centimetres [8 inches]; about the seventeenth week of
gestation; showing the complete analogy in the develop-
ment of the hair and the teeth.

.«, Filous follicle quite well developed, with its bulb
forcing back the epithelial cells and forming a cap for itself;
b, simple epithelial bourgeon; c, epithelial bourgeon, with
the bulb just appearing.

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208 SUMMARY.

Fig. 41. — Section taken from the jaw of an embryonal
calf, after the rupture of the epithelial cord. (Magnified
260 diam.)

This cut embraces the region external to the follicle (a),
which latter is not represented in this figure, b, Epithelial
buddings upon the follicular wall; c, epithelial lamina, still
entire; E, E, buddings from the epithelial cord; F, globular
epithelial mass in the lamina.

Fig. 42. — Section taken from a bovine embryo, and em-
bracing the same territory represented in Fig. 41.

a, Segment of the follicular wall; b, epithelial buddings
upon the wall; c, prismatic layer of the oral epithelium;
d, oral epithelium; E,E, debris and buddings of the cord;
F, epithelial globules from the debris of the epithelial
lamina. (Magnified 100 diameters.)

For the physiological importance attributed to these
epithelial proliferations, see pp. 66 and 179.

Fig. 41.

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210 SUMMARY.

Fig. 43. — Vertical transverse section of the lower jaw of
a human foetus, 56 centimetres [22f inches] in length;
corresponding to about the period of birth. (Magnified 80
diam.)

b, Osseous formation; d, oral epithelium; E, lowest layer
of the Malpighian stratum; F, debris of the epithelial
lamina; g, enamel-organ; H, dental bulb; I, follicular
wall; j, cap of dentine and enamel; K, debris of the second-
ary cord; L, bulb of the permanent tooth, capped with the
enamel-organ.

Fig. 44. — Dental follicle of a permanent tooth of a cat;
vertical and transverse section. From a preparation of
Thiersch. (Magnified 14 diam.) Taken from the fifth edi-
tion of Kolliker's Elements of Human Histology.

A, Dental bulb, the external zone of which is formed by
the odontoblasts; b, dentine; c, enamel; d, "internal epithe-
lial layer of the adamantine organ or adamantine mem-
brane" [the layer of prismatic or columnar cells that we
denominate ameloblasts]; e, gelatinous tissue of the en-
amel-organ [stellate reticulum]; /, external epithelial layer
of the adamantine organ [enamel -organ]; g, internal layer
of the dental sac or follicular wall; h, external layer of the
same.

[The white space seen between the layer of ameloblasts
and the developing enamel is evidently accidental. See
remarks on Fig. 24.]

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INDEX

Adamantine membrane, 22, 109
Aggregations of epithelium, 125
Amelification, 91
Ameloblasts, 83, 91, 109, 151, 153
Amorphous layer, 17, 101
Apophyses, 28

Atrophy of Meckel's Cartilage, 37
Authors' introduction, 47
Bar of the solipeds, diastema, 55
Basement membrane, 14, 17, 21, 24, 88 and 89
Bourgeons, 28, 44, 122, 130
primitive, 135
secondary, 134, 136
Bourrelet, epithelial band, 54
Cartilago dentalis, 54
Cell, apology for use of the term, 44
Cells, epidermal, 25

epithelial, in different stages of development, 20
aculeated, imbricated, prickle, spinous, ridged, 20
columnar, 21, 23
cylindrical, 21
polygonous, 22, 116, 132
prismatic, 21, 81, 83
Cement, coronal, 111
Cemental organ. 111
Chronology of the dental follicle, periods of appearance of

its parts, 147
Chronological table of dental follicle, 160
Corium, 12, 14
Cord of temporary teeth, 128

permanent teeth, 128
Corneous stratum, 15, 17, 19, 20, 23
Corneous leaf or plate, of Remak, 18
Cortical layer of enamel-organ, 82
Cuticle, 17
Cutis vera, 14

Definition of foetus, embryo, follicle and bourgeon, 41
Dental follicle, 89, 105, 111

its genesis and formation, theories of criticised, 169

INM-.X.

213

Dental follicle, definition of, 42

origin and formation of, 4!)
Dental germ, 107

groove. 135. 150 •
sacs, LOT
sacculus, 42, '.'s
Dentine-bulb, 25, 42,75,90,100, L12

origin and growth of, 98
I)entine-cap. 152
Dentinal papilla, 25, 42, 75. 96
Dentinal sheet of tissue, 66
Dermal stratum, 21
tissues, 16
Dermis (derm or dermal, 12, 14. 16, 24. 2G
Diagram of mucous membrane. 13
Diastema, or bar. 55

Diverticulum, 132 ' .

Double pellucid layer, between ameloblasts and tissues ot

pulp. H8
Early development of the jaws, 27

Ecderon and enderon, 14 _ _ . , 1Aft

Embryos, canine, ovine, bovine and equine, studyot, lbi to iw
Kmbryoplastic elements of incipient dental-bulb, 95, 1WJ
Enamel, formation of, due to internal epithelium. 82, »6
Enamel-cells, ameloblasts, 83

-membrane, 22
Enamel-organ, 21, 42, 83. 90, 93, 96, 151
its development, 65
as fully developed, 75
as part of the dental follicle, 107
of the permanent tooth. 142
Enamel-organs of supernumerary t< eth, 66
Epiblast, 18, 25
Epidermal cells. 25

membrane, Is
stratum. 21
Epidermis, 11, 14. 1!). 114. 119
Epithelial band, description of. 54. 58, 62, 14!)

Kiilliker's discovery of, 175. 176
Epithelial cord, 66. 150

as determining the place and form of tooth. .».
when its course is finished, 123
of permanent follicles, point_ of origin, 13 1, 138
in embryo of two months, 150
Epithelial lamina, its origin and development, 62

at the period the enamel-organ loses connection
with it. 105

214 INDEX.

Epithelial lamina, phenomena located in it after rupture of
cord, 115

sometimes the place of origin of cords of anterior
permanent teeth, 13?

place of origin of the cord of first permanent mo-
lar, 143, 144

proliferations, phenomena of, 121, 122
Epithelial ridg'e or band, its origin, etc., 51
Epithelium, 11, 13, 18, 112

pavimentous or tessellated, 20
Errors of early observations, cause of, 175
External germinal layer, or epiblast, 18

osseous arch, 35
First permanent molar, its place of origin, 144
Follicle, definition of, 43

epithelial proliferations upon, 121
Follicular wall, 42, 108

network of vessels upon, 112

buddings upon, 120, 122

not closed at twelfth week, 152
Formation of enamel, due to internal epithelium, 82, 83
Formed material, Beale, 22, 23
Fusiform bodies, composing incipient dental bulb, 95
Genesis and growth of the dental follicle, theories of criti-
cised, 169

of follicle, true order of, 174

of follicle, etc., summary of facts concerning, 180, 181

of follicle, conclusions regarding, 181 to 184
Glandula? tartaricse, 124
Hare-lip, its origin, 31
Horny layer of the epidermis, 23
Human embryo, relation between size and age, 148
Incisive or intermaxillary bourgeons, origin of, etc., 29, 31

period of union with the maxillary bourgeons, 50
Incisive region, 40
Initial spheroid, of Guillot, 173
Intermaxillary bones, 30, 38

processes, 31

suture, 39
Intermediate membrane, of Henle, 12, 18
Internal cartilaginous arch, 35

epithelium of the enamel-organ of Kolliker, 22
Introduction, authors', 47

Lamina, epithelial, 62, 70, 105, 115, 137, 144
Laminated membrane of follicular wall, 106
Last molar, its origin, 144

INDEX. -I'

Lateral buddings of primitive cord, • •-'
Malleus, termination of Meckel's cartilage, 33

ossification of its cartilage . :'>i
Malpighian stratum, 15, 17. 30, 84
Manimillated form of mcipienl dental bulb, ■'•>
Mandibular processes, 82
Maxillary bourgeons, union with intermaxillary, ■>"

rampart, 52
Meckel's cartilage, 27, 32, 50, 149
Membrana adamantina, of Raechkow, 22

Eboris, 91

praVurmativa of Rasehkow. 18. 88, 90. 101, 10(5
prsformativa of Huxley, 88, 90
propria, 12
Mesoblast, the origin of the dermis, 19
period at which developed, 25
Mucosa, 1-4
Mucous layer, 12
Mucous membrane, 9

Odontol .lasts, tissue in which they first appear. 101
Odonto>n.nir parj, or the generating part of the teeth, ol
Odontomes, 159 .

Oral epidermis, divisible into two lamina1, 19
Origin and formation of the dental follicle, 49
Origin and formation of the dental bulb and follicular wall,

93
Pars papillaris, or i r> j- .->-
Papillary layer. f ' ' 10 ,- .,-

Pars reticularis, reticulary layer. Id, lo. &a
Pellucid layer. v^
Periplast ol Huxley. 22

Permanent follicles that Lave been preceded by temporary
ones, 129
commencement of, 153
Phenomena that follow formation of follicle, etc., 115
Plateau of the prismatic cells. s7
Premaxillse, 40

Primitive bourgeon of the follicle, 65
Primitive papilla. 95
Primitive follicle after rupture of cord. 123

modifications in surrounding parts. 185
in relation to origin of secondary cord, 188
Primitive cord, prolongations of, 128

point from which secondary bourgeon starts, 140
Prismatic layer of cells, 28, 59, 82, 109
Processes, apophyses or bourgeons, 28

2 1 6 INDEX.

" Proper" mucous membrane, 13, 14

Pulp of enamel- organ, stellate arrangement of, 80

Raschkow's theory of origin of follicle, 171

Reticulary layer, 13, 15, 25

Ruptured cord, 135

Scarf-skin, 17

Second molar, origin of, 144

Secondary bourgeon, its descent into dental groove, 134

in lower animals, 136

and point of origin, direction it takes, 140
Secondary cord, 139

development of, 153

separation of, 154, 155
Secondary follicle, 123, 141
Semilunar area, origin of dentine germs, 98
Skin, analogous to mucous membrane, 16
Stellate bodies, transformation of cells of the enamel-organ,

69, 77
Stratum corneum, 23

Malpighii, 12, 20

Malpighii prismatic layer derived from, 59

intermedium, 84, 153
Subcutanea, 15
Subdermal areolar tissue, 25
Subdermis, 15
Submucous tissue, 25
Submucosa, 13, 15
Superior maxillary processes, 31
Tartaric glands, 124
Tela mucosa, 13, 15

Temporary follicles, generally the source of the twenty an-
terior permanent teeth, 137
The epithelial lamina and genesis of enamel-organ, 62
The mode of origin of follicles of permanent teeth, 127
Third molar, place of origin, 138, 145
Tongue, apophyses, etc., 28
Translator's introduction, 9
True epidermis, 17

Tubercles, bourgeons, processes, etc., 28
Upper jaw, its development, 50
Vessels of the bulb, 126
Visceral arch, 28
Wisdom tooth, its origin, 138, 144

— _

RK880

Legros

L52
Copy 1

Origin and formation of the dental
follicle.

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