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cut between the seventeenth and twenty-fifth year, but are often delayed until a
very much later period, and occasionally never appear.
The set of teeth which, as indicated above, begin to appear in the infant about

Ibe the sixth month, are known as the deciduous teeth (0.T. temporary, or milk teeth); oht whilst those which succeed them and form the adult equipment are the permanent

ular teeth.

The deciduous teeth are twenty in number, and are named as follows in each jaw, beginning at the median plane :—dentes incisivi, or incisor teeth, central and lateral; So ac dens caninus, or canine tooth ; dentes molares, or molar teeth, first and second ; or Uke more briefly, two incisors, one canine, two molars. This is conveniently expressed als by the “dental formula” for the deciduous teeth in man, which shows the number

of each class of teeth above and below on sper
one side of the mouth, viz. :-

TE
_Substantia
adamantina

i. 3, c. ), m. š = 20.
The permanent teeth, thirty-two in

Tie Dec
number, are named dentes incisivi, or in-
cisor teeth, central and lateral ; dentes
canini, or canine teeth; dentes præmolares,

at the
dentis premolar (O.T. bicuspid) teeth; dentes estas

molares, molar teeth; and are arranged
as follows in each jaw, beginning at the
median plane :-central incisor, lateral in-

cisor, canine, 1st premolar, 2nd premolar, je other Neck 1st molar, 2nd molar, and 3rd molar or

Pue in te
dens serotinus (O.T. wisdom tooth). The
dental formula for the permanent set in
man is thus:-

i. s, c. ), pm. s, m. f = 32.
General Form and Structure. – A
tooth consists (Fig. 880) of (1) the corona
dentis or crown, the portion projecting
above the gum. It varies in shape in the
different teeth, and in all, except the
incisors and canines, bears on its masticating
surface a number of tubercles, the tubercula

coronæ (O.T. cusps), varying in number from
Bone

two to five in the different teeth; (2) the

collum dentis or neck, the faintly constricted Alveolar periosteum or root-membrane

part which is surrounded collar-wise by the Fig. 880. —- Vertical Section of Canine Toote, gum, and connects the crown with (3) to illustrate its various parts, and its structure.

the radix dentis or root, the portion of the tooth embedded in the alveolus of the jaw. In the majority of teeth, namely, in all except the molars, the root, as a rule, is single, or nearly so, and consists of a long, tapering, conical, or flattened piece, perfectly adapted to the alveolus in which it lies. In the molar teeth (and in some of the others occasionally) the root is divided into two or three tapering or flattened roots or fangs. apex of each root there can be made out, even with the naked eye, a minute opening, the foramen apicis, through which the vessels and nerves enter the tooth.

When a section of a tooth is made (Fig. 880), it will be seen that the interior of the body is occupied by a cavity of some size, called the cavum dentis or tooth cavity, which is filled in the natural state by the soft and sensitive tissue known as the pulpa dentis or tooth pulp. The tooth cavity gradually narrows, and is prolonged into each root of the tooth as a slender tapering passage, the canalis radicis (root-canal), which opens at the apical foramen already referred to. Through these root-canals, which also contain some pulp, the vessels and uerves, which enter at the apex, pass to the interior of the tooth.

Short diverticula of the pulp cavity are prolonged into the bases of the tubercles

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the molar and premolar teeth, and in the incisors also there are similar slight longations of the cavity towards the angles of the crown.

The roots of the teeth are embedded in the alveoli or sockets of the jaws, to ich they are accurately adapted, and firmly united (Fig. 880) by a highly scular layer of connective tissue—the periosteum alveolare. This is attached the wall of the alveolus on the one hand and to the root of the tooth on the er, whilst above it is continuous with the connective tissues of the gum.

So accurately are the root and the alveolus adapted to each other over their
ole extent, and so firmly does the periosteum bind them together, that, under
rmal conditions, the tooth is quite firmly fixed in the bone, and no movement
the root within the alveolus can take place; the vessels and nerves entering at

apex are thus secured against pressure or strain.
When, however, the alveolar periosteum is inflamed it becomes swollen and exquisitely sensi-
e; the tooth, as a result of the swelling, is pushed partly out of its socket, its crown projects
ve those of its neighbours, and strikes against the opposing tooth when the mouth is closed,
ing rise to much pain and discomfort.
The neck, although the term is useful, can scarcely be recognised as a distinct constriction in the
manent teeth; it corresponds to the line along which the gum and alveolar periosteum meet,
along which the gum is united to the tooth ; but, as already pointed out, the gum does not
p at the neck, but forms a free fold which surrounds the base of the crown collar-wise for a
rt distance. The outline of the margin of the gum opposite the labial and lingual surfaces of

crown is usually concave, but opposite the contact surfaces of the tooth it is convex, and
ches much nearer to the edge of the crown than on the other surfaces.
In the incisors and canines the tooth cavity, which is about to the diameter of the tooth,
ses very gradually into the root-canal (Fig. 880), so that it is difficult to say where one ends
1 the other begins. The reverse is the case in the molars, whilst the premolars are somewhat
riable in this respect.

Tartar is a hard calcareous deposit from the saliva (salivary calculus), often found on the teeth ar their necks. It is composed of lime salts, and its deposit is largely determined by the esence of organisms (leptothrix, etc.) in the mouth.

DENTES PERMANENTES.

The permanent teeth (Figs. 881 and 882) are thirty-two in number, sixteen ove and sixteen below, or eight in each half of both jaws; and, although they n be grouped under four heads—incisors, canines, premolars, and molars—the dividual teeth differ so much in their characters that each tooth requires a parate description.

Descriptive Terms.Before describing the permanent teeth, it is requisite that rtain terms which are employed to denote the surfaces of the teeth should be defined. his is a matter of some importance, seeing that the terms medial and lateral, anterior d posterior, cannot, owing to the curvature of the dental arches, be properly applied all the teeth in the same sense. The terms given below have been adopted seeing that ley are free from the danger of misconception.

The part of a tooth which comes in contact with the teeth of the opposite jaw is known
i the facies masticatoria (grinding or masticating surface) (Fig. 883). The surface in
ontact with or looking towards its predecessor in the row is known as the facies medialis
i incisors and canines, facies anterior in premolars and molars; the opposite surface,
amely, that which looks towards its successor in the row, is known as the facies lateralis

incisors and canines, facies posterior in molars and premolars. The surface which
oks towards the tongue is the facies lingualis (lingual surface), and that looking in
e opposite direction, i.e. towards the lips and cheek, the facies labialis (labial surface).
he portion of a tooth which touches its neighbour in the same row is known as the
icies contacta contact surface).

Dentes Incisivi (Figs. 881 and 882). — The incisor teeth, four in number in ach jaw, are used specially for cutting the food, hence their name. The crown f each is chisel-shaped, and presents a labial surface which is convex in all

a concave lingual surface, and a chisel-like edge, which, when first ut, is surmounted by three small tubercles separated by two grooves. These ubercles, however, are soon worn down, and the edge becomes straight or nearly 0. Owing to the fact that the upper incisors overlap those in the mandible, the

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III. Accessory Digestive Glands.—The largest of these is the liver (hepar), which occupies the upper and right portion of the abdominal cavity, immediately below the diaphragm, and its secretion—the bile—is conveyed into the duodenum by the bile duct (ductus choledochus). The pancreas, next in size, lies across the front of the vertebral column, with its right end or head resting in the concavity of the duodenum, into which its secretion flows through the pancreatic duct. The salivary glands consist mainly of three large paired glands, parotid, submaxillary, and sublingual (glandula parotis, submaxillaris, and sublingualis), and their ducts, which convey the saliva, open into the mouth. The saliva is a mechanical lubricant, which facilitates swallowing and the movements of the tongue in speaking and masticating, and also plays an important part in the chemical processes of digestion.

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CAVUM ORIS.

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1. Parts.—Rima oris, vestibulum oris, cavum oris proprium.
2. Boundaries.-1. Labia oris—their structure.

2. Buccæ- their structure.
3. Palatum (palatum durum, palatum molle)-arrangement and structure.

4. Isthmus faucium.'
3. Structures found in the Mouth.-Gingivæ, gums.

Dentes, teeth.

Lingua, tongue. 4. Glandulæ oris. — Buccal and salivary glands. The mouth is the upper expanded portion which forms the first division of the alimentary canal. It lies between the maxillæ and mandible, bounded externally by the lips and the cheeks, and roofed in by the palate. It contains the teeth and greater part of the tongue; and the ducts of the salivary glands open

The philtrum

into it. The cavity is divisible into
two portions, the vestibule and the

cavity proper of the mouth. These
-Raphe of palate

are separated from one another by the

alveolar ridges, gums, and teeth of the
Uvula

maxillæ and mandible. The cavity of
Pharyngo- the mouth narrows at the back to a
-palatine arch
Pharyngo- slight constriction, marked by a vertical
nasal
isthinus fold on each side, called the arcus
Palatine

glosso-palatinus (O.T. anterior pillar
tonsil
Glosso- of the fauces), and between them the
palatine arch

cavity of the mouth is continuous with

that of the pharynx. - Tongue

Rima Oris.—The aperture of the mouth is bounded above and below by the corresponding lips, which, by their junction at the sides, form the labial commissures. In a state of rest, with the lips in apposition, the rima appears as a slightly curved line, corresponding

in length to the interval between the FIG. 874.-OPEN Mouth SHOWING PALATE AND

first premolar teeth, and in level to PALATINE TONSILS.

a line drawn across just below the It also shows the two palatine arches, and the pharyngo- middle of the upper incisor crowns nasal isthmus

, through which the naso-pharynx, above, The shape of the rima varies with communicates with the oral portion of the pharynx, every movement of the lips, from the below.

resting linear form, curved like the conventional bow, to a circular or oval shape when the mouth is widely open, or the "pursed-up” condition produced by the contraction of the orbicularis orie muscle.

Vestibulum Oris.-The vestibule of the mouth lies immediately internal to the

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aperture of the mouth. It is that portion of the cavity which occupies the interval between the lips and cheeks externally, and the teeth and gums internally.

In the normal resting condition, when the mouth is closed and the lips and the teeth are in contact, its cavity is practically obliterated by the meeting of its walls, and it becomes merely a slit-like interval, with a narrow roof and floor formed by the reflection of the mucous membrane from the deep surface of the lips and cheeks to the corresponding gum. This reflection is interrupted in the median plane by a small but prominent fold of the mucous membrane, the frenulum, which connects the back of each lip to the front of the gum. The upper frenulum is the better developed, and is readily brought into view by everting the lip. The frenulum of the lower lip is not always present.

On the outer wall of the vestibule, opposite the crown of the second upper molar, upon a variably developed eminence, is placed the small opening of the duct of the parotid gland, which

Stylo-glossus conveys the

Stylo-pharyngeus saliva from the paro

Glossopharyngeal Deep part of submaxillary gland pulled back tid gland to the

Submaxillary ganglion

Stylo-hyal mouth.

ligament

Submaxillary duct (Wharton's)

Cut edge of mucous membrane

Lingual nerve When the teeth

Sublingual gland

Sublingual artery are in contact the vestibule communi

glossus cates with the cavity of the mouth only through

the smail and irregular spaces left between the opposing teeth, and posteriorly, on either side, by a wider but variable aperture be

Genio-hyoid
tween the last molars
and the ramus of the

Lingual artery
Lingual artery
Middle constrictor

Hypoglossal nerve mandible.

Hyoid branch of lingual artery Advantage is some

FIG. 875.-DISSECTION OF SUBMAXILLARY REGION. times taken of the presence of this aperture for the introduction into the cavity of the mouth of liquid food in certain cases-trismus, anchylosis, etc.—in which the jaws are rigidly closed.

On the outer wall of the vestibule, the anterior border of the masseter can be distinctly felt with the finger, when the muscle is thrown into a state of contraction. Still further back, the front of the coronoid process, bearing the lower part of the insertion of the temporal muscle, can also be made out. The spheno-mandibular ligament, which corresponds to, and is felt along with, the anterior border of the internal pterygoid muscle, is distinguishable as a pliant ridge when the finger is carried from the front of the coronoid process behind the last molar tooth into the cavity of the mouth.

In addition to the duct of the parotid, the ducts of numerous small glands which are embedded in the lips and cheeks open into the vestibule.

Under normal conditions, as pointed out above, the lips and cheeks lie against the teeth and gums, obliterating the cavity of the vestibule, and helping, with the aid of the tongue, to keep the food between the grinding surfaces of the molar teeth during mastication. In facial palsy, however, owing to the paralysis of their muscles, and particularly of the buccinator muscle, the lips and cheeks fall away from the dental arches, and allow the food to pass out from between the teeth and to accumulate in the vestibule.

Cavum Oris Proprium.—The cavity proper of the mouth is the space situated within the dental arches, extending backwards to the glosso-palatine arches (O.T. anterior pillars of the fauces). Its boundaries consist of a roof, a floor, and a margin, formed by the teeth and gums. The roof is formed by the hard palate and the anterior portion of the soft palate, while the floor is formed by the anterior part of the tongue in the middle, and on each side by the reflection of the mucous membrane from the side of the tongue to the mandible.

On each side of the tongue, and in front of it, when it is at rest, there is only a slit or sulcus between the tongue and the gums, into which the ducts of the submaxillary and sublingual glands open.

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If, however, the tongue is raised, there is exposed a limited space to which the term sublingual space is more usually applied (Fig. 876).

The term "floor of the mouth,” or sublingual region, is frequently applied to the muscular and other structures, especially the mylo-hyoid muscles, which fill in the interval between the two halves of the body of the mandible. These structures, with the hyoid bone, form the basis upon which the tongue and the mucous membrane of the sublingual space are supported, and they extend from the symphysis menti, in front, to the body of the hyoid bone, behind.

The sublingual region (Fig. 876) is covered by the mucous membrane between the deep surface of the gum and the inferior aspect of the tongue. When the tip of the tongue is raised the membrane forms in the median plane a prominent fold,

the frenulum linguæ, stretching from
the floor of the mouth to the inferior
surface of the tongue. On each
side of the frenulum, near its

junction with the floor, there can
The philtrum

be readily made out a prominent
soft papilla, the caruncula sub-
lingualis, on which the opening of
the duct of the submaxillary gland

(0.T. Wharton's duct) may be seen
Anterior gland of (Fig. 876). Running laterally and
tongue

posteriorly, on each side, from this, Layer of muscle cut and occupying the greater part of to show the gland

the floor of the mouth, there is a
Plica fimbriata

well-marked ridge,plica sublingualis,
due to the projection of the under-
lying sublingual gland. Most of

the ducts of this gland open near
Frenulum lingua

the crest of the ridge on each side.
Duct of the submax. There is also another fold, called
illary gland
Openings of ducts of the plica fimbriata, medial to each of
the submaxillary
gland

the others, on the inferior surface
Sublingual gland

of the tongue.

When the mouth is closed, and re-
Plica sublingualis, spiration is carried on through the nose,
with openings of

the cavum oris is reduced to a slit-like
ducts of sublingual
gland

space, and practically obliterated by the

tongue coming in contact with the palate Fig. 876.—OPEN MOUTH WITH TONGUE RAISED, AND THE above, and with the gums and teeth SUBLINGUAL AND ANTERIOR GLANDS EXPOSED. laterally and in front.

When the The sublingual gland of the left side has been laid bare by the mouth is slightly open and the teeth

removal of the mucous membrane ; to expose the anterior nearly in contact, the tongue becomes lingual gland of the right side a thin layer of muscle, in somewhat concave or grooved along the addition to the mucous membrane, has been removed. A median plane, and leaves a channel-like branch of the lingual nerve is seen running on the medial space between it and the palate, while it aspect of the gland. The profunda vein also is faintly remains in contact with the roof and indicated on this side.

gums laterally. By depressing the hyoid

bone together with the root of the tongue, the cavum oris can be increased to a considerable size even when the teeth are in contact. Finally, by the simultaneous descent of the mandible and hyoid bone with the tongue, and the ascent of the soft palate, the cavity is increased to its greatest dimensions (Fig. 874).

Labia Oris.- The lips are the two movable folds, covered superficially by skin, and on their deep surface by mucous membrane, which surround the rima oris. The meeting of the lips at each side constitutes the commissure, and bounds the angle of the mouth (angulus oris). Laterally, they are prolonged into the cheeks, with which they are continuous. The junction of the lips and cheek is marked on the surface by the sulcus naso-labialis, which passes downwards and laterally from the margin of the nose towards the angle of the mouth, while the sulcus mento-labialis separates the lower lip from the chin. The upper lip presents on its superficial surface a well-marked vertical groove, the philtrum, bounded by two distinct ridges descending from the columella nasi (Fig. 876); inferiorly the groove

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