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supply the blood-vessels, which they are known to influence. Most of them, however,
appear to end in the secreting alveoli. These they reach for the most part as non-




THE SALIVARY GLANDS. 23

medullated fibres, and, after piercing the basement membrane, end in an open
arborescence of the finest varicose fibrils, ramifying between and around the cells of
the alveoli (fig. 30).



BECENT LITERATURE OF THE SALIVARY GLANDS.

Berkeley, H. J. , The intrinsic nerves of the submaxillary gland of Mus mvsculus, Johns
Hopkins' Hosp. Sep., vol. v., 1894.

Hermann, Ueber d. Zusammensctzung der Glandula xubmax. , <Lc., Wiirzburg, 1878.

Biederxnann, Zur Histologie und Physiologic er Schleimseh'etion, Sitzungsberichte cler Kaiserl.
Akademie fler Wissensch. zu Wien, Math. Naturwiss. Klasse, Abt. iii., 1894.

Bizzozero, Gr., und Vassalo, Q-., Ueber die Er ~e ugung und die physiologische Regeneration der
Driisenzetten bei den Sdugetieren, Yirchow's Archiv, Bd. ex., 1887.

Carlier, The so-called "hibernating gland" of the hedgehog, Journ. of Anat. and Physio!.,
xxvii., 1893.

Chievitz, J. H. , Beitrdje zur Entwickelungsgeschichte dtr Fpeicheldriiitcn, Arch. f. Anat. und
Physiol., Anat. AUh., 1885.

Flemming-, Walter, Ueber Bau und Einthtilung der Drttsen, Arch. f. Anat. u. Physiol.,
Anat. Abthlg., 1888.

Frenkel, Moise, Sur les modifications du tissu conjonctif des glandes et en particvlicr de la
glande sous-maxillaire, Anat. Anzeiger, Jalivg. viii., 1893.

van Gehuchten, A., Le mecanisme de la secretion, Anat. Anzeig., Bd. vi., 1890.

Qruber, "W., C'ongenitaler Mangel beuler Glandidce submaxillares, Virchow's Archiv, cii., 1885.

Kamocki, Ueber die Entwickl. der Bermann' schcn tubulosen .Driisen, Intern. Monatschr. f. Anat.,
Bd. i., 1884.

Klein, E., Histological Notes, Quart. Journ. of Micr. Science, xxi., 1881 ; On the lymphatic
system and the minute structure of the salivary glands and pancreas, Ibid., xxii., 1882.

Korolkow, P., Die Nervenendiguiigen in den Speicheldrusen, Anatom. Anz., Jahrg. vii., 1892.

Kultschitzky, N., Zur Lehre v. feineren Bau der Speicheldrusen, Zeitschr. f. wiss. Zool., Bd.
xli., 1885.

Lang-ley. J. N., On the histology of the mucous salivary glands, and on the behaviour of their
mucous constituents, Journ. of Physiol., vol. x., 1889.

Laserstein, Sigfried, Ueber die Anfdnge der Absonderungswege in den Speicheldriisen und im
Pankreas, Arch. f. d. ges. Physiol., Bd. lv., 1893.

List, Joseph Heinrich, Ueber den feineren Bau Schleim-sezerniercnder Driisenzellen, nebat
Bemerkungen ilber den kekrctionsprozcss, Anat. Anzeiger., Jahrg. iv., 1889.

Loewenthal, N., Zur Kenntnis der Glandula submaxillaris einiger Sdugetiere, Anat. Anzeiger,
Bd. ix., 1894 ; Hlstorische-kritische Notiz u. d. Glandula submax., Ibid , Bd. x., 1895 ; and Arch. f.
mikr. Anat., Bd. xl., 1892.

Mayer, S., Adenologische Mitteilungen, Anat. Anze ; g., Bd. x., 1895.

Muller, Erik, Zur Anatomic der Speicheldriisen, Nordiskt med. Arkiv, 1893.

Nicolas, A., Contribution a V etude des cellules glandulaires, Le protoplasma dex elements des
ylandes albumineuses, Archives de physiologic normale et pathologique, Annee xxiv., 1892.

Paulsen, Ed., Bemerkungen iiber Sekretion und Bau der Schleimdruscn, Archiv fur mikroskop.
Anatomic, Band xxviii., 1886.

Poirier, Paul, Absence des parotides, Bulletins de la Societe anatomique de Paris, Annee Ixiii.,
1888.

Kanvier, L., Etude anatomique des glandes connues sous les noms de sous-maxillaire et sub-
linguale chez les mammiferes, Archives de physiologic, Annee xviii., 1886 ; Les membranes
muqueuses et le systeme glandulaire, Journal de micrographie, t. x. ; Le mecanisme de la secretion,
Ibid., t. xi., 1887.

Retzius, Gustaf, Ueber die Anfdnge der Drusengdnge und die Nervenendigungen in den
Speicheldrusen des Mundes, Biolog. Untersuch. , N. F. iii., 1892.

Ricard, A., De quelques rapports anatomiques de la glande sous-maxittaire, Bull. Soc. Anat.,
Paris, 1889.

Seidenmann, M., Beit, zur Micro2)hysiologie der Schleimdrusen, Internat. Monatschr. f. Auat.
u. Physiol., Bd. x., 1893.

Solger, Bernh., Zur Kenntniss der secernirendenZellcn der Glandula- submaxillaris des Menschen,
Anat. Anzeiger, Bd. ix. , 1894, and " Nachtrag " in the same.

Steiner, Hermann, Ueber das Epithel der Ausfiihrungsgange der grosscren Driisen des
Menschen, Archiv f. mikr. Anat., Bd. xl., 1892.

Zumstein, J. J., Ueber die Unterkieferdrilseneiniger Sduger, 1891.



24 ORGANS OF DIGESTION.

THE TEETH.

In the human subject as in the great majority of mammals the dentition is
diphyodont, that is two sets of teeth make their appearance in the course of life, of
which the first comprehends the temporary or milk teeth, while the second is the
permanent set. 1 The temporary teeth are twenty in number, ten in each jaw, and
the permanent set consists of thirty-two, sixteen above and sixteen below.

The human dentition is also heterodont ; the teeth, instead of all having the
same form (homodont condition), differ considerably in their size, shape, and
function. The twenty temporary teeth consist of four incisors, two canines, and
four multicuspids or molars above and below. The thirty-two permanent teeth are
four incisors, two canines, four bicuspids or premolars, and six molars in each jaw.
There are no bicuspids among the temporary teeth, the eight deciduous molars
preceding eight bicuspids of the permanent set. The relative position and arrange-
ment of the different kinds of teeth may be expressed by the following formula,
which also exhibits the relation between the two sets in these respects :



Temporary teeth



Permanent teeth UPP- .



MO.


CA.


IN.


IN.


CA.


MO.










>

2


]
1


2
2


2

2


1
1


2
2





10
10


}


= 20


BI.


CA.


IN.


IN.


CA.


BI.


MO.








2


1


2


2


1


2


3 =


IK


")


QO



2123 = 16 )



Or they may be written more simply thus :

(2.1.2
Milk teeth - -



Permanent teeth



(2.1.2



As the typical mammalian dentition is In 3 , C,



3
and Mo,



on each side of each jaw. it



follows that three pairs on each side are suppressed in man. Not unfrequently one or more of

Fig. 31. LOWER ASPKCT OF SUPERIOR DENTAL

ARCH AND HARD PALATE. (Muhlreiter. )

these normally suppressed teeth appear,
sometimes in a well developed condition,
but much more frequently they are rudi-
mentary. From the position these super-
numerary teeth occupy it is probable that
the missing teeth are the second incisor and
the first and fourth premolars (A. Wilson).

The curve occupied by the teeth of
the upper jaw is elliptical, and of the
lower parabolic. It is not broken by
any interval or diastema as is the case
in most mammals. The span of the
upper dental arch is rather larger
than that of the lower one, so that

the teeth of the upper jaw slightly overlap those of the lower, both in front
and at the sides. While there is a slight diminution in the height of the crowns
of the teeth from the incisors backwards to the wisdom-teeth, there is in man

1 The three permanent molars are by some regarded as belonging to the first dentition, since they
do not take the place of any of the milk teeth, but are formed independently in a backward extension of
the dental germ.




THE TEETH.



no abrupt change of level along the range. In consequence of the large pro-
portionate breadth of the upper central incisors, the other teeth of _the upper
jaw are thrown somewhat outwards, so that in closure of the jaws the canines and
bicuspids come into contact partly with the corresponding lower teeth, and partly





Fig. .2. UPPER ASPECT OP LOWER DENTAL AHCH AND BODY OF LOWEK JAW. (Miililreiter. )

with those next following ; and in the case of the molars, each cusp of the upper
lies behind the corresponding cusp of the lower teeth. Since, however, the upper
Fig. 33. LABIAL ASPECT OK THE RIGHT HALF

OF THE TWO DENTAL ARCHES TO SHOW THE
RELATION BETWEEN THF, UPPER AND LOWKR

TEETH. (Zuckerkandl.)

molars and especially the wisdom-teeth
are smaller than those below, the dental
ranges terminate behind nearly at the
same point in both jaws (see figs. 38
and 34).

In Europeans the upper incisors project
in front of the lower incisors, but it has
been shown by Turner that in some, at
least, of the Australian aborigines this is
not the case, the cutting edges of 'the lower
incisors projecting as far forwards as those of the upper.

It is well known that the teeth of certain races are larger in relation to the general
stature of the individual than in others. Flower has investigated this question so far as the
premolars and molars are concerned. He has constructed a dental ln<lu.r by comparing the
distance between the anterior surface of the first premolar and the posterior surface of the
wisdom-tooth with the basin-nasal length of the skull. He divides the various races

Fig. 34. LINGUAL ASPECT OF THE LEFT

HALF OF THE TWO DENTAL ARCHES.

(Zuckerkandl. )

according to their dental index into
mwrodimt, VKtodont, and mcf/ftffunt.
The microdont section contains the
white races, the mesodont the Mon-
golian or yellow races, and the mega-
doiit the black races, including the
Australians.

In consequence of the curve of the dental arch, such terms as anterior,
posterior, internal and external, when used in the description of the surfaces of the




ORGANS OF DIGESTION.



teeth, are liable to lead to confusion, to obviate which special names must be
employed. The surface of a tooth directed towards the lips or cheek is therefore
called labial or buccal, and that towards the tongue the lingual, while the terms
proximal and distal are used to represent the surfaces that would look towards and

Fig. 3">. VERTICAL SECTION OP PREMOLAR OP
CAT. 15 DIAMETERS. (Waldeyer. )

c, is placed in the pulp-cavity, opposite
the cervix or neck of the tooth ; the part
above is the crown, that below is the root
(fang). 1, enamel with radial and concen-
tric markings ; 2, dentine with tubules and
incremental lines ; 3, cement or crusta
petrosa, with bone corpuscles ; 4, dental
periosteum : 5, bone of lower jaw.

away from the median plane were
the teeth arranged in a straight
line passing outwards from fche
mesial incisor.

A tooth consists of three por-
tions, viz., one which projects above
the gums and is named the bod// or
croim, another fixed in the alveolus
or socket, the root, consisting of a
fang or fanys and a third, inter-
mediate between the other two, and,
from being more or less constricted,
named the neck. The size and form
of each of these parts vary in the
different kinds of teeth.

The roots of the teeth are
accurately fitted to the alveoli of
the jaws, in which they are im-
planted. Each alveolus is lined
r>y periosteum (dental periosteum,
fig. 35, 4), which also invests the
contained tooth as high as the
neck, and is blended above with the
dense' tissue of the gums. The
fangs of all the teeth taper from the
cervix to the point, and this form together with their accurate adjustment to the
alveolus has the effect of distributing the pressure during use over the whole socket,
and of preventing it from unduly bearing on the point of the fang, through which
the blood-vessels and nerves enter.

SPECIAL CHARACTERS OF THE TEETH.

THE PERMANENT TEETH. The incisors (fig. 36), eight in number, are the four
front teeth in each jaw, and are so named from being adapted for cutting or
dividing the food. Their crotvns are chisel-shaped (c), and have a sharp horizontal
cutting edge, which by continued use is bevelled off behind in the upper teeth, but
in the lower ones is worn down in front, where it comes into contact with the over-
lapping edges of the upper teeth. Before being subjected to wear the horizontal
edge of each incisor is marked by three small prominent points, separated by two
slight notches (fig. 3G, d). The labial surface of the crown is slightly convex, both
from above downwards, and from side to side. The lingual surface is concave,




THE TEETH.



27




especially from above downwards, and presents a prominence termed the liasal
ridge or cingulum. The proximal and distal surfaces are triangular_with the base
at the gum, and the apex towards the cutting edge. The fang is long, single,
conical and compressed at the sides, where it sometimes, though rarely, presents a
slight longitudinal furrow (as in c}. The lower incisor teeth are placed vertically
in the jaw, but the corresponding upper teeth are directed obliquely forwards. The
upper incisors are, on the whole, larger than the lower ones. Of those in the upper
jaw the mesial incisors are the larger ; but in the lower jaw the mesial incisors are
the smaller, and are, indeed, the smallest of all the incisor teeth. The cingulum is

Fig. 36. INCISOR TEETH OF THE UPPER AND LOWER

JAWS.

a, front view of the upper and lower mesial incisors ;

b, front view of the upper and lower lateral incisors ;

c, lateral view of the upper and lower mesial incisors,
showing the chisel shape of the crown ; a groove is seen
marking slightly the fang of the lower tooth ; d, the
upper and lower mesial incisor teeth before they have
been worn, showing the three points on the cutting
edge.

absent in the lower incisors, but sometimes
in the upper lateral incisors, and less fre-
quently in the upper mesial incisors, it is
developed into a distinct lingual cusp (fig. 37).
The canine teeth (fig. 38), four in
number, are placed one on each side, above
and below, next to the lateral incisors.
They are larger and stronger than the
incisor teeth. The crown is thick and
conical, its labial surface decidedly convex, and the lingual concave. It may be
compared to that of a large incisor tooth the angles of which have been removed,
so as to leave a single central point or cusp, whence the name cuspidate applied to
these teeth. The point always becomes worn down by use. The fang of the canine
teeth is single, conical, and compressed at the sides : it is longer than the fangs of

Fig. 37. , b, C, LINGUAL SURFACE OF UPPKR INCISOR TEETH SHOW-
ING VARIATIONS IN FORM ; IN a THE CINGULUM IS WELL MARKED.

(Zuckerkandl.)

any of the other teeth, and is so thick as to cause a
prominence of the alveolar arch.

The upper canines, popularly called the eye-teeth, are
larger than the lower, and in consequence of this, as well
as of the greater width of the upper range of incisors,
they are thrown a little farther outwards than the lower
ones. On the lingual surface of the upper canine a well-marked ridge passes from
the apex of the cusp to the cingulum, where there is frequently a distinct tubercle.
The lower canine has neither a lingual ridge nor cingulum. The root of the upper
canine is almost invariably single, while that of the lower is often bifid at its apex.
In the dog-tribe, and in the carnivora generally, these teeth acquire a great size,
and are fitted for seizing and killing prey, and for gnawing and tearing it when
taken as food.

The bicuspids (fig. 39), also called premolars, are four in each jaw ; they are
shorter and smaller than the canines, next to which they are placed. The crown is
compressed proximo-distally, and both its labial and lingual surfaces are convex.
The grinding surface shews two cusps a large labial and a smaller lingual





28



ORGANS OF DIGESTION.




separated by a deep fissure. The fang is compressed in the same direction
as the crown, and is grooved on its proximal and distal surfaces so as to

Fig. 38. CANINE TOOTH OF THE UPPER JAW.
_a, front view ; 6, lateral view, showing the long fang grooved on the side.

shew a tendency to be divided into a labial and a lingual
portion.

The upper bicuspids differ very considerably from the lower,
and while in the latter there is a decided distinction between
the first and second, in the case of the two upper bicuspids
there is but little difference. The labial surface of the crown
b a of the first upper bicuspid has a vertical ridge passing from

its apex upwards towards the neck ; this ridge is bounded by
two lateral depressions (see a, fig. 39). The lingual surface of the crown is smaller
and more convex both longitudinally and transversely than the labial aspect. It

Fig. 39. FIRST BICUSPID TOOTH OF THE UPVER AND LOWER JAWS.

a, labial view ; b, lateral view, showing the lateral groove of the fang,
and the tendency in the upper to division.

has usually two roots, a labial and a lingual ; sometimes
only one, and more rarely three, two labial and one lingual.
In the second upper bicuspids the labial and lingual surfaces
are nearly equal, and the labial ridge is indistinct, while the
fang is more frequently single than in the first bicuspid.
The lower bicuspids are smaller than the upper ones, their
cusps are less deeply divided, and the lingual surface is
much less convex than the labial. In the upper bicuspids
the two cusps are separated by a deep fissure, while in the
lower they are united by a low -ridge. The lower bicuspids
have generally single roots, but occasionally the root is
divided into a labial and a lingual fang. The first lower
bicuspid has sometimes only one cusp distinctly marked, viz. the labial, and in
that case it approaches in figure to a canine tooth. The second bicuspid is larger

Fig. 40. FIRST MOLAR TOOTH OF THE UPPER AND LOWER JAWS.
They are viewed from the buccal aspect.

than the first, and its lingual cusp is nearly as prominent as the
labial one, whereas in the first bicuspid the lingual cusp is much
smaller.

The molar teeth (fig. 40), true or large molars, or grinders, are
twelve in number, and are arranged behind the bicuspid teeth,
three on each side, above and below. They are distinguished by the
large size of the crown, and by the great width of its grinding
surface. The first molar is the largest, and the third is the smallest,
in each range, so as to produce a gradation of size in these teeth.
The last of the range, owing to its late appearance through the gum,
is called the wisdom-tooth. The crowns of the molar teeth are low
and cuboid in their general form. Their labial and lingual surfaces
are convex, but the proximal and distal surfaces are flattened.
The grinding surface is nearly square in the lower teeth, and rhomboidal in the
upper, the corners being rounded off ; it bears four or five trihedral tubercles or






THE TEETH.



29




cusps (whence the name midticuspidati), separated from each other by a crucial
depression.

The crown of the first upper molar bears four cusps, situated at trie angles of
the masticating surface ; of these the proximo-lingual is the largest, and is usually
connected with the labio-distal cusp by a low oblique ridge. This tooth has
occasionally a fifth cusp situated on the lingual side of the proximo-lingual cusp ;

Fig. 41. GRINDING SURFACE OF THE UPPER MOLARS.

(Zuckerkandl.)

A, on right side ; tlie first molar has four cusps, and the second and
third three each.

B, another set from the left side, with the same number of cusps as in
A, except that a small additional cusp is seen on the lingual side of the
proximo-lingual cusp of the first molar. The third molar is larger than
the second.

this additional cusp is small, and rarely, if ever, reaches the
grinding surface. The second upper molar is generally

described as having four cusps, but according to Zuckerkandl and Rose there are
often only three. Zuckerkandl found four cusps in 45'6 per cent, of Europeans,
the cusps being reduced to three in 54-4 per cent., while in the lower races four
cusps were found in 73'5 per cent. Rose's results agree essentially with those of
Zuckerkandl. In the upper wisdom-tooth the two lingual cusps are usually blended.
The crowns of the lower molars, which are larger than those of the upper, have
five cusps, the additional one being placed between the two distal ones, and

Fig. 42. GRINDING SURFACE OF THE LOWKK MOLARS ON LEFT SIDE. (Zuckerkandl.)

In this series the first molar has five cusps, the second 4, and the third 4, and the
teeth diminish in size from the first to the third.

rather to the outer side. Not unfrequently the second molar has only
four cusps, but this reduction in the number of cusps rarely affects the
first and third molars. The third molar is usually as large as and
sometimes even larger than the second. The fangs of the molar teeth
are multiple. In the first and second molars of the upper jaw the
fangs are three in number, viz. two labial and one lingual ; the labial fangs are
short, divergent, and directed towards the antrum of the superior maxilla, while
the lingual fang is larger and longer and directed towards the palate, its distal
border extending as far back as the labio-distal fang. The first and second
molars of the lower jaw have each two broad compressed fangs, one proximal
and the other distal ; they are grooved on the faces that are turned towards each
other as if each consisted of two fangs fused together. In the wisdom-teeth of
both jaws the fangs are often collected into a single irregular, conical mass, which
is either directed backwards in the substance of the jaw, or curved irregularly ; this
composite fang sometimes shows traces of subdivision, and there are occasionally
two fangs in the lower teeth and three in the upper.

HOMOLOGIES OF THE TEETH. Two main views are held as to the phylogeny of the
multicuspidate teeth of various mammals, such as the molars in man. According' to Rose and
others these teeth are formed by the fusion of a number of originally simple cones, such as.
are found in the Reptilia. The evidence offered in support of this view is mainly embryo-
logical. On the other hand, Cope and Osborn, from a study of the teeth in a large series of
fossil mammals, hold that the primitive form of mammalian molar was a single cone, to which
all the other cusps have been successively added.

In fishes, amphibia, and reptilia, in place of two series of teeth such as occur in mammals,
there is throughout life a constant succession of series which replace one another from behind
forwards. There can be little doubt that the two series, milk and permanent, of mammals,
represent a part, at least, of the successive series of reptilian teeth. Some considerable amount,




30



ORGANS OF DIGESTION.







of discussion has of late years taken place as to which of the two dentitions is the primary,
for although in higher mammals the milk dentition is the first to appear, in marsupials it
appears to be absent ; and it has hence been inferred that it is really only of secondary
development. The most recent researches seem, however, to show that the milk dentition is
represented in a rudimentary form even in marsupials, and it would further appear that in
exceptional instances in higher mammals, and in man, a third, and even a fourth, series of
teeth may be produced in connection with persistent remains of the dental lamina, behind
and lateral to the permanent teeth ; this being an apparent reversion to the reptilian con-
ditions of dental succession. For a full discussion of these and other points in connection
with the homologies of the teeth, see Schwalbe, ' Ueber Theorien der Dentition," Verhandl.
d. anat. G-esellschaft, Anat. Anzeiger. 1894.

THE MILK-TEETH (fig. 43). The temporary or milk-teeth are distinguished
from the permanent by the marked bulging of the crown close to the neck, so that

Fig. 43. MILK TEETH OF THE RIGHT

SIDE OF THK UPPER AND LOWER JAWS.

, the incisors ; b, the canines ; c,
the molar teeth.

the latter shews a well-marked
constriction. The temporary in-
cisors and canine teeth resemble
those of the permanent set in
their general form, but they are
of smaller dimensions, and all
their characteristic markings are
much less decided, especially
those in the canines.

The temporary molars are larger than the bicuspids which succeed them. The
hinder of the two is much the larger, being, indeed, the largest of all the milk-teeth.
The first upper milk molar has only three cusps, two labial and one lingual ; the
second has four. The first lower temporary molar has four cusps, and the second
five, of which in the latter case three are labial. The fangs of the temporary molars
resemble those of the permanent set, but they are smaller and are more divergent
from the neck of the tooth.

STRUCTURE OF THE TEETH.

On making a section of a tooth, it is found to be hollow within (fig. 44). The
form of the cavity bears a general resemblance to that of the tooth itself ; it occupies

Fig. 44. SECTIONS OF AN INCISOR AND MOLAR TOOTH.

the interior of the crown, and extends along each
fang, at the point of which it opens by a small



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