1. Oral cavity.Tongue.Palatine. Salivary glands
2. Teeth, their structure.Periodont structure
3. Permanent teeth
Lesson No 11
Theme
1. Oral cavity.Tongue.Palatine. Salivary glands
SPLANCHNOLOGY
is doctrine about viscera, which disposed in thoracic, abdominal and pelvic
cavities, also in head and neck. Internal organs may be divided into digestive,
respiratory, urinary and genital systems and endocrine glands.
The digestive system is a group of
organs that work like wrecking equipment to break down the chemical components
of food, through the use of digestive juices, into tiny nutrients which can be
absorbed to generate energy for the body. Digestion begins in the mouth with
the teeth, which grind the food into small particles; the tongue, a powerful
muscle which detects "good" and "bad" flavours in food and
manipulates the food between the teeth for chewing, and saliva, a watery fluid
which lubricates chewing and swallowing and begins the process of digestion. The
digestive system begins in the mouth, continues in the pharynx (throat) and
oesophagus and into the "gut" region: the stomach, small and large
intestines, the rectum and the anus. Food is chewed, pulped and mixed with
saliva to become a soft mass which will easily travel down the oesophagus. The
tongue traps the food and forces it into the throat, which is a mass of muscles
and tissues which transports food into the gut system for final processing and
distribution. The liver and the pancreas also secrete digestive juices that
break down food as it passes through the digestive ducts. Not all that we eat
can be digested, so the waste must be disposed of in an efficient way. It may
not be a savoury ending for the food or drink we thought was so delicious in
the mouth, but it is just as important for our health.
The apparatus for the digestion (Apparatus Digestorius; Organs Of Digestion)
of the food consists of the digestive tube and of certain accessory
organs.
The Digestive Tube (alimentary canal) is a
musculomembranous tube, about
The accessory organs are the teeth, for purposes of
mastication; the three pairs of salivary glands—the parotid,
submandibular, and sublingual—the secretion from which mixes with
the food in the mouth and converts it into a bolus and acts chemically on one
of its constituents; the liver and pancreas, two large glands in
the abdomen, the secretions of which, in addition to that of numerous minute
glands in the walls of the alimentary canal, assist in the process of
digestion.
The Development of the Digestive Tube.—The
primitive digestive tube consists of two parts, viz.: (1) the fore-gut,
within the cephalic flexure, and dorsal to the heart; and (2) the hind-gut,
within the caudal flexure.
Between these is the wide opening of the yolk-sac, which is gradually narrowed
and reduced to a small foramen leading into the vitelline duct. At first the
fore-gut and hind-gut end blindly. The anterior end of the fore-gut is
separated from the stomodeum by the buccopharyngeal membrane.
the hind-gut ends in the cloaca, which is closed by the cloacal membrane.
Human embryo about fifteen days old. Brain and heart represented from
right side. Digestive tube and yolk sac in median section.
The Mouth.—The mouth is developed
partly from the stomodeum, and partly from the floor of the anterior portion of
the fore-gut. By the growth of the head end of the embryo, and the formation of
the cephalic flexure, the pericardial area and the buccopharyngeal membrane
come to lie on the ventral surface of the embryo. With the further expansion of
the brain, and the forward bulging of the pericardium, the buccopharyngeal
membrane is depressed between these two prominences. This depression
constitutes the stomodeum. It is lined by ectoderm, and is separated
from the anterior end of the fore-gut by the buccopharyngeal membrane. This
membrane is devoid of mesoderm, being formed by the apposition of the stomodeal
ectoderm with the fore-gut entoderm; at the end of the third week it
disappears, and thus a communication is established between the mouth and the
future pharynx. No trace of the membrane is found in the adult; and the
communication just mentioned must not be confused with the permanent isthmus
faucium. The lips, teeth, and gums are formed from the walls of the stomodeum,
but the tongue is developed in the floor of the pharynx.
The visceral arches extend in a ventral direction between
the stomodeum and the pericardium; and with the completion of the mandibular
arch and the formation of the maxillary processes, the mouth assumes the
appearance of a pentagonal orifice. The orifice is bounded in front by the
fronto-nasal process, behind by the mandibular arch, and laterally by the
maxillary processes.
With the inward growth and fusion of the palatine processes, the stomodeum is
divided into an upper nasal, and a lower buccal part. Along the free margins of
the processes bounding the mouth cavity a shallow groove appears; this is
termed the primary labial groove, and from the bottom of it a downgrowth
of ectoderm takes place into the underlying mesoderm. The central cells of the
ectodermal downgrowth degenerate and a secondary labial groove is
formed; by the deepening of this, the lips and cheeks are separated from the
alveolar processes of the maxillæ and mandible.
The Salivary Glands.—The salivary glands
arise as buds from the epithelial lining of the mouth; the parotid appears
during the fourth week in the angle between the maxillary process and the
mandibular arch; the submandibular appears in the sixth week, and the
sublingual during the ninth week in the hollow between the tongue and the
mandibular arch.
Head end of human embryo of about thirty to thirty-one days.
Floor of pharynx of human embryo about twenty-six days old
The Tongue is developed in the
floor of the pharynx, and consists of an anterior or buccal and a posterior or pharyngeal
part which are separated in the adult by the V-shaped sulcus terminalis. During
the third week there appears, immediately behind the ventral ends of the two
halves of the mandibular arch, a rounded swelling named the tuberculum
impar, which was described by His as undergoing enlargement to form the
buccal part of the tongue. More recent researches, however, show that this part
of the tongue is mainly, if not entirely, developed from a pair of lateral
swellings which rise from the inner surface of the mandibular arch and meet in
the middle line. The tuberculum impar is said to form the central part of the
tongue immediately in front of the foramen cecum, but Hammar insists that it is
purely a transitory structure and forms no part of the adult tongue. From the
ventral ends of the fourth arch there arises a second and larger elevation, in
the center of which is a median groove or furrow. This elevation was named by
His the furcula, and is at first separated from the tuberculum impar by
a depression, but later by a ridge, the copula, formed by the forward
growth and fusion of the ventral ends of the second and third arches. The
posterior or pharyngeal part of the tongue is developed from the copula, which
extends forward in the form of a V, so as to embrace between its two limbs the
buccal part of the tongue. At the apex of the V a pit-like invagination occurs,
to form the thyroid gland, and this depression is represented in the adult by
the foramen cecum of the tongue. In the adult the union of the anterior
and posterior parts of the tongue is marked by the V-shaped sulcus terminalis,
the apex of which is at the foramen cecum, while the two limbs run lateralward
and forward, parallel to, but a little behind, the vallate papillæ.
Floor of pharynx of human embryo about thirty days old.
The Palatine Tonsils.—The palatine tonsils
are developed from the dorsal angles of the second branchial pouches. The
entoderm which lines these pouches grows in the form of a number of solid buds
into the surrounding mesoderm. These buds become hollowed out by the
degeneration and casting off of their central cells, and by this means the
tonsillar crypts are formed. Lymphoid cells accumulate around the crypts, and
become grouped to form the lymphoid follicles; the latter, however, are not
well-defined until after birth.
Sketches in profile of two stages in the development of the human
digestive tube.
The Further Development of the Digestive Tube.—The upper part of the fore-gut becomes dilated to form the pharynx in relation to which the branchial arches are
developed (see page 65); the succeeding part remains tubular, and with the
descent of the stomach is elongated to form the esophagus. About the fourth
week a fusiform dilatation, the future stomach, makes its appearance, and
beyond this the gut opens freely into the yolk-sac. The opening is at first
wide, but is gradually narrowed into a tubular stalk, the yolk-stalk or vitelline
duct. Between the stomach and the mouth of the yolk-sac the liver
diverticulum appears. From the stomach to the rectum the alimentary canal is
attached to the notochord by a band of mesoderm, from which the common
mesentery of the gut is subsequently developed. The stomach has an additional
attachment, viz., to the ventral abdominal wall as far as the umbilicus by the
septum transversum. The cephalic portion of the septum takes part in the
formation of the diaphragm, while the caudal portion into which the liver grows
forms the ventral mesogastrium.
The stomach undergoes a further dilatation, and its two curvatures can be recognized,
the greater directed toward the vertebral column and the lesser toward the
anterior wall of the abdomen, while its two surfaces look to the right and left
respectively. Behind the stomach the gut undergoes great elongation, and forms
a V-shaped loop which projects downward and forward; from the bend or angle of
the loop the vitelline duct passes to the umbilicus. For a time a considerable part of the loop
extends beyond the abdominal cavity into the umbilical cord, but by the end of
the third month it is withdrawn within the cavity. With the lengthening of the
tube, the mesoderm, which attaches it to the future vertebral column and
carries the bloodvessels for the supply of the gut, is thinned and drawn out to
form the posterior common mesentery. The portion of this mesentery
attached to the greater curvature of the stomach is named the dorsal
mesogastrium, and the part which suspends the colon is termed the mesocolon.
About the sixth week a diverticulum of the gut appears just behind the opening
of the vitelline duct, and indicates the future cecum and vermiform process.
The part of the loop on the distal side of the cecal diverticulum increases in
diameter and forms the future ascending and transverse portions of the large
intestine. Until the fifth month the cecal diverticulum has a uniform caliber,
but from this time onward its distal part remains rudimentary and forms the vermiform
process, while its proximal part expands to form the cecum. Changes also take
place in the shape and position of the stomach. Its dorsal part or greater
curvature, to which the dorsal mesogastrium is attached, grows much more
rapidly than its ventral part or lesser curvature to which the ventral
mesogastrium is fixed. Further, the greater curvature is carried downward and
to the left, so that the right surface of the stomach is now directed backward
and the left surface forward,
a change in position which explains why the left vagus nerve is found on the
front, and the right vagus on the back of the stomach. The dorsal mesogastrium
being attached to the greater curvature must necessarily follow its movements,
and hence it becomes greatly elongated and drawn lateralward and ventralward
from the vertebral column, and, as in the case of the stomach, the right
surfaces of both the dorsal and ventral mesogastria are now directed backward,
and the left forward. In this way a pouch, the bursa omentalis, is
formed behind the stomach, and this increases in size as the digestive tube
undergoes further development; the entrance to the pouch constitutes the future
foramen epiploicum or foramen of Winslow. The duodenum is
developed from that part of the tube which immediately succeeds the stomach; it
undergoes little elongation, being more or less fixed in position by the liver
and pancreas, which arise as diverticula from it. The duodenum is at first
suspended by a mesentery, and projects forward in the form of a loop. The loop
and its mesentery are subsequently displaced by the transverse colon, so that
the right surface of the duodenal mesentery is directed backward, and, adhering
to the parietal peritoneum, is lost. The remainder of the digestive tube
becomes greatly elongated, and as a consequence the tube is coiled on itself,
and this elongation demands a corresponding increase in the width of the intestinal
attachment of the mesentery, which becomes folded.
Front view of two successive stages in the development of the digestive
tube.
The primitive mesentery of a six weeks’ human embryo, half schematic.
Abdominal part of digestive tube and its attachment to the primitive or
common mesentery. Human embryo of six weeks.
At this stage the small and large intestines are attached to
the vertebral column by a common mesentery, the coils of the small intestine
falling to the right of the middle line, while the large intestine lies on the
left side.
The gut is now rotated upon itself, so that the large
intestine is carried over in front of the small intestine, and the cecum is
placed immediately below the liver; about the sixth month the cecum descends
into the right iliac fossa, and the large intestine forms an arch consisting of
the ascending, transverse, and descending portions of the colon—the transverse
portion crossing in front of the duodenum and lying just below the greater
curvature of the stomach; within this arch the coils of the small intestine are
disposed .
Sometimes the downward progress of the cecum is arrested, so
that in the adult it may be found lying immediately below the liver instead of
in the right iliac region.
Further changes take place in the bursa omentalis and in the
common mesentery, and give rise to the peritoneal relations seen in the adult.
The bursa omentalis, which at first reaches only as far as the greater
curvature of the stomach, grows downward to form the greater omentum, and this
downward extension lies in front of the transverse colon and the coils of the
small intestine Above, before the
pleuro-peritoneal opening is closed, the bursa omentalis sends up a
diverticulum on either side of the esophagus; the left diverticulum soon
disappears, but the right is constricted off and persists in most adults as a
small sac lying within the thorax on the right side of the lower end of the
esophagus. The anterior layer of the transverse mesocolon is at first distinct
from the posterior layer of the greater omentum, but ultimately the two blend,
and hence the greater omentum appears as if attached to the transverse colon .
The mesenteries of the ascending and descending parts of the colon disappear in
the majority of cases, while that of the small intestine assumes the oblique
attachment characteristic of its adult condition.
Reconstruction of a human embryo of
The lesser omentum is formed, as indicated above, by a
thinning of the mesoderm or ventral mesogastrium, which attaches the
stomach and duodenum to the anterior abdominal wall. By the subsequent growth
of the liver this leaf of mesoderm is divided into two parts, viz., the lesser
omentum between the stomach and liver, and the falciform and coronary ligaments
between the liver and the abdominal wall and diaphragm .
Diagrams to illustrate two stages in the development of the digestive
tube and its mesentery. The arrow indicates the entrance to the bursa
omentalis.
Final disposition of the intestines and their vascular relations.
(Jonnesco.) A. Aorta. H. Hepatic artery. M, Col. Branches
of superior mesenteric artery. m, m’. Branches of inferior mesenteric
artery. S. Splenic artery
Schematic figure of the bursa omentalis, etc. Human embryo of eight
weeks.
The Rectum and Anal Canal.—The hind-gut is
at first prolonged backward into the body-stalk as the tube of the allantois;
but, with the growth and flexure of the tail-end of the embryo, the body-stalk,
with its contained allantoic tube, is carried forward to the ventral aspect of
the body, and consequently a bend is formed at the junction of the hind-gut and
allantois. This bend becomes dilated into a pouch, which constitutes the entodermal
cloaca; into its dorsal part the hind-gut opens, and from its ventral part
the allantois passes forward. At a later stage the Wolffian and Müllerian
ducts open into its ventral portion. The cloaca is, for a time, shut off from
the anterior by a membrane, the cloacal membrane, formed by the
apposition of the ectoderm and entoderm, and reaching, at first, as far forward
as the future umbilicus. Behind the umbilicus, however, the mesoderm
subsequently extends to form the lower part of the abdominal wall and symphysis
pubis. By the growth of the surrounding tissues the cloacal membrane comes to
lie at the bottom of a depression, which is lined by ectoderm and named the ectodermal
cloaca.
FIG. 990– Diagrams to illustrate the development of the greater omentum
and transverse mesocolon. (See
enlarged image)
Tail end of human embryo from fifteen to eighteen days old.
Cloaca of human embryo from twenty-five to twenty-seven days old
The entodermal cloaca is divided into a dorsal and a ventral
part by means of a partition, the urorectal septum which grows downward from
the ridge separating the allantoic from the cloacal opening of the intestine
and ultimately fuses with the cloacal membrane and divides it into an anal and
a urogenital part. The dorsal part of the cloaca forms the rectum, and the
anterior part of the urogenital sinus and bladder. For a time a communication
named the cloacal duct exists between the two parts of the cloaca below
the urorectal septum; this duct occasionally persists as a passage between the
rectum and urethra. The anal canal is formed by an invagination of the ectoderm
behind the urorectal septum. This invagination is termed the proctodeum,
and it meets with the entoderm of the hind-gut and forms with it the anal
membrane. By the absorption of this membrane the anal canal becomes
continuous with the rectum. A small part
of the hind-gut projects backward beyond the anal membrane; it is named the post-anal
gut and usually becomes obliterated and disappears. 159
Tail end of human embryo, from eight and a half to nine weeks old.
Oral cavity is
bordered up by palate, which separates the oral cavity from the nasal
cavities and the nasal part of the pharynx or nasopharynx; in front and
laterally – by cheeks, from below – by oral diaphragm (formed by
mylohyoid muscle). The cavity of the mouth is placed at the commencement
of the digestive tube it is a nearly oval-shaped cavity, which consists of two
parts: an outer, smaller portion, the vestibule, and an inner, larger
part, the proper mouth cavity. Both portions communicate each other
through the space behind last molars and through the fissure between upper and
lower teeth. The vestibule is the slit like space between the
lips, cheeks, the teeth and the gingivae. The vestibule communicates with the
exterior through the orifice of the mouth - the opening, through which food and
other substances pass into the oral cavity. Duct of parotid salivary gland
opens into vestibule.
Cheeks
have a muscular component - buccinator muscle. Superficial to the fascia
covering this muscle is the buccal fat pad - Bisha body. It gives the
cheeks their rounded contour, particularly in infants for sucking the milk. The
lips and cheeks function as a unit (for example - during blowing, eating,
sucking, and kissing). They act as an oral sphincter in pushing food from the
vestibule to the oral cavity proper. Mucous membrane of the cheeks contains
small buccal salivary glands.
Palate
consists of two regions: 1. the anterior two-thirds or bony part - the hard
palate. 2. the mobile posterior one-third or fibromuscular part – the soft
palate. The hard palate formed by palatine processes of the maxillae and
the horizontal plates of the palatine bones covered by mucous membrane, which
contains small salivary glands. Posteriorly the hard palate is continuous with
the soft palate. The soft palate contains a membranous aponeurosis and
is a movable, fibromuscular fold that is attached to the posterior edge of the
hard palate. The soft palate or velum palatinum extends
posterior inferiorly to a curved free margin from which hangs a conical process
- the uvula. It separates the nasopharynx superiorly from the oropharynx
inferiorly. Laterally the soft palate is continuous with the wall of the
pharynx and is joined to the tongue and pharynx by the palatoglossal and
palatopharyngeal arches, between which locate the palatine tonsil.
Deep to the palatal mucosa are mucous glands. The soft palate is formad by 5
muscles:
Tensor veli
palatini muscle – stretches velum palatine and widens aperture
of uditory tube;
Levator veli
palatini muscle – lifts soft palatine;
Uvulae muscle –
lifts and shortens the uvula;
Palatoglossus
muscle – lowers the velum palatinum, narrows the fauceus and
lifts the lingual root;
Palatopharyngeus
muscle –narrows the fauceus and lifts the pharynx.
Teeth, structure.Periodont
structure
The teeth may be
divided into deciduous (primary) teeth in chilhood age and permanent teeth in
adult. Each tooth consists of three parts: crown, neck and root. The crown
has 5 surfaces: lingual, vestibular (labial or buccal), contact (proximal
and distal), occlusal. The neck is the part of the tooth
between the crown and the root. The root is fixed in the alveolar
socket by a fibrous periodontal ligament (gomphosis).
Tooth
is composed of dentin that is covered by enamel over the crown -
and cementum over the root. The pulp cavity contains connective
tissue, blood vessels, and nerves. The last pass through the root canal
and the apical foramen. The roots of the teeth fit into sockets called dental
alveoli in the alveolar process of the mandible and maxillae. Each socket
is lined with periodontal membrane.
Types
of Teeth
Medial
and lateral incisors - have a single
root and chisel-shaped crown. Action: they cut off portions of food.
Canine -
has a single root, conical crown. Action: holding and bite the food.
Premolar
- has a single root, sometimes upper tooth has
bifurcated root. Crown carries two tubercles. Action: crushing the food.
Molar
– upper teeth have three roots, lower teeth have two roots.
Crown carries 3-5 tubercles on occlusal surface. Action: grinding the food.
Formula
of the deciduous (milk) teeth is 2102. Formula of the permanent teeth is 2123.
It means that child before 6 years of age in each side of upper and lower jaw
own 2 incisors, 1canine, no premolar and 2 molars. Permanent teeth include 2
incisors, 1canine, 2 premolars and 3 molars.
Permanent teeth of upper dental arch, seen from below.
Permanent teeth of right half of lower dental arch, seen from above
Age terms of
eruption of deciduous teeth and permanent teeth:
Type
of tooth |
Deciduous
|
Permanent
|
Incisors |
6
– 9 months |
7
– 9 years |
Canines |
16
- 20 months |
10
– 13 years |
First
Premolar |
- |
10
– 12 years |
Second
Premolar |
- |
11
–15 years |
First
Molar |
12
- 15 months |
6
–7 years |
Second
Molar |
20
– 24 months |
13
– 16 years |
Third
Molar ("wisdom tooth") |
- |
18
– 30 years |
Order of cutting of milk teeth:
• Incisors;
• First molars;
• Canines;
• Second molars.
Maxillæ at about one year
Child
should have 20 teeth till end of second year of age.
Order of eruption of permanent teeth:
• first inferior molars;
• Medial incisors and first superior molars;
• Lateral incisors;
• First premolars;
• Canines;
• Second premolars;
• Second molars;
• Third molars (called "wisdom tooth", present not in all
person).
The complete temporary dentition (about
three years), showing the relation of the developing permanent teeth.
There
are 32 permanent teeth. Mutual arrangement of superior and inferior dental
arches during closing the mouth called bite. There are the physiological
and pathologic bites.
The gingivae are composed of
fibrous tissue that is covered with mucous membrane. They are firmly attached
to the margins of the alveolar processes (tooth sockets) of the jaws and to the
necks of the teeth.
The tongue is situated
partly in the mouth and partly in the oropharynx. It consists of three parts:
apex, body and root. Also tongue has dorsum (upper surface), inferior
surface, margin and median sulcus. The dorsum of the tongue carries
V-shaped sulcus terminalis with foramen cecum at the apex of this
sulcus. Sulcus terminalis divide dorsum linguae into anterior presulcal
and posterior postsulcal parts. There is lingual tonsil on the mucous
membrane of root.
Lingual
frenulum attaches anterior presulcal portion to the floor of
the mouth. Fimbriate plicae pass laterally from frenulum. Sublingual
plica runs laterally and backward from frenulum base, also it carries sublingual
caruncle. Ducts of submandibular and sublingual glands open
there. The mucous membrane on the oral part of the tongue carries numerous of
the papillae:
·
The filiform papillae and conic
papillae - contain afferent nerve endings that are sensitive to touch.
·
The fungiform papillae - small
and mushroom-shaped. They usually appear as pink or red spots. Contain taste
receptors located in the taste buds.
·
The vallate papillae - are the
largest papillae (1 to
·
The foliate papillae - are
small lateral folds of the lingual margins. They contain taste receptors.
There
are four extrinsic and four intrinsic muscles of tongue.
Extrinsic
group contains four muscles:
1. THE GENIOGLOSSUS MUSCLE arises
by a short tendon from the mental spine of the mandible. Insertion:
enters the tongue inferiorly and its fibres attach to the entire dorsum of the
tongue. Actions: depresses the tongue and its posterior part
protrudes it.
2. THE HYOGLOSSUS MUSCLE arises
from the body and greater horn of the hyoid bone. Insertion: the
side and inferior aspect of the tongue. Actions: depresses the
tongue, pulling its sides inferiorly.
3. THE STYLOGLOSSUS MUSCLE originates
from the anterior border of the styloid process near its tip and from
the stylohyoid ligament. Insertion: the side and inferior aspect
of the tongue. Actions: lifting the tongue and curls its sides to
create a trough during swallowing.
4. THE PALATOGLOSSUS MUSCLE starts
from the palatine aponeurosis of the soft palate. Insertion:
the side and the lateral part of the tongue. Actions: elevates
the posterior part of the tongue.
The intrinsic muscles
are mainly concerned with altering the shape of the tongue, making it broad or
narrow. Their fibbers run in three directions.
1. THE SUPERIOR LONGITUDINAL
MUSCLE forms a thin layer deep to the mucous membrane on the dorsum of the
tongue, running from its apex to its root. Origin: the submucous fibrous layer
and the lingual septum. Insertion: mainly into the mucous membrane. Actions:
curls the tip and sides of the tongue superiorly, making the dorsum of the
tongue concave.
2. THE INFERIOR LONGITUDINAL Muscle consists of a narrow band close
to the interior surface of the tongue. Actions: curls the tip of
the tongue inferiorly, making the dorsum of the tongue convex.
3.THE TRANSVERSE Muscle lies deep to the superior
longitudinal muscle. Origin: the fibrous lingual septum. Insertion:
submucous fibrous tissue. Actions: narrows and increases the
height of the tongue.
4. Vertical Muscle originates in dorsum of the tongue. Insertion:
site of the tongue. Actions: flattens and broadens the tongue;
acting with the transverse muscle, it increases the length of the tongue.
The Tongue (lingua) is the principal organ of the sense of taste, and an important organ of
speech; it also assists in the mastication and deglutition of the food. It is
situated in the floor of the mouth, within the curve of the body of the
mandible.
Its Root (radix linguæ base) is directed
backward, and connected with the hyoid bone by the Hyoglossi and Genioglossi
muscles and the hyoglossal membrane; with the epiglottis by three folds (glossoepiglottic)
of mucous membrane; with the soft palate by the glossopalatine arches; and with
the pharynx by the Constrictores pharyngis superiores and the mucous membrane.
Its Apex (apex linguæ tip), thin and
narrow, is directed forward against the lingual surfaces of the lower incisor
teeth.
Its Inferior Surface (facies inferior linguæ
under surface) is connected with the mandible by the Genioglossi; the
mucous membrane is reflected from it to the lingual surface of the gum and on
to the floor of the mouth, where, in the middle line, it is elevated into a
distinct vertical fold, the frenulum linguæ. On either side
lateral to the frenulum is a slight fold of the mucous membrane, the plica
fimbriata, the free edge of which occasionally exhibits a series of
fringe-like processes.
The apex of the tongue, part of the inferior surface, the
sides, and dorsum are free.
The Dorsum of the Tongue (dorsum linguæ)
(Fig. 1014) is convex and marked by a median sulcus, which divides it into
symmetrical halves; this sulcus ends behind, about
The Papillæ of the Tongue are projections of
the corium. They are thickly distributed over the anterior two-thirds of its
dorsum, giving to this surface its characteristic roughness. The varieties of
papillæ met with are the papillæ vallatæ, papillæ
fungiformes, papillæ filiformes, and papillæ simplices.
The mouth cavity. The apex of the tongue is turned upward,
and on the right side a superficial dissection of its under surface has
been made
The papillæ vallatæ (circumvallate
papillæ) are of large size, and vary from eight to twelve in number.
They are situated on the dorsum of the tongue immediately in front of the
foramen cecum and sulcus terminalis, forming a row on either side; the two rows
run backward and medialward, and meet in the middle line, like the limbs of the
letter V inverted. Each papilla consists of a projection of mucous membrane
from 1 to
The papillæ fungiformes (fungiform
papillæ),
more numerous than the preceding, are found chiefly at
the sides and apex, but are scattered irregularly and sparingly over the
dorsum. They are easily recognized, among the other papillæ, by their
large size, rounded eminences, and deep red color. They are narrow at their
attachment to the tongue, but broad and rounded at their free extremities, and
covered with secondary papillæ.
The papillæ simplices are similar to those of
the skin, and cover the whole of the mucous membrane of the tongue, as well as
the larger papillæ. They consist of closely set microscopic elevations of
the corium, each containing a capillary loop, covered by a layer of epithelium.
Muscles of the Tongue.—The tongue is divided
into lateral halves by a median fibrous septum which extends throughout its
entire length and is fixed below to the hyoid bone. In either half there are
two sets of muscles, extrinsic and intrinsic; the former have their origins
outside the tongue, the latter are contained entirely within it.
The extrinsic muscles (Fig. 1019) are:
Genioglossus.
Hyoglossus.
Chondroglossus.
Styloglossus.
Extrinsic muscles of the tongue. Left side.
The Genioglossus (Geniohyoglossus) is a flat
triangular muscle close to and parallel with the median plane, its apex corresponding
with its point of origin from the mandible, its base with its insertion into
the tongue and hyoid bone. It arises by a short tendon from the superior
mental spine on the inner surface of the symphysis menti, immediately above the
Geniohyoideus, and from this point spreads out in a fan-like form. The inferior
fibers extend downward, to be attached by a thin aponeurosis to the upper part
of the body of the hyoid bone, a few passing between the Hyoglossus and
Chondroglossus to blend with the Constrictores pharyngis; the middle fibers
pass backward, and the superior ones upward and forward, to enter the whole
length of the under surface of the tongue, from the root to the apex. The
muscles of opposite sides are separated at their insertions by the median
fibrous septum of the tongue; in front, they are more or less blended owing to
the decussation of fasciculi in the median plane.
The Hyoglossus, thin and quadrilateral, arises
from the side of the body and from the whole length of the greater cornu of the
hyoid bone, and passes almost vertically upward to enter the side of the
tongue, between the Styloglossus and Longitudinalis inferior. The fibers
arising from the body of the hyoid bone overlap those from the greater cornu.
The Chondroglossus is sometimes described as a part
of the Hyoglossus, but is separated from it by fibers of the Genioglossus,
which pass to the side of the pharynx. It is about
A small slip of muscular fibers is occasionally found,
arising from the cartilago triticea in the lateral hyothyroid ligament and
entering the tongue with the hindermost fibers of the Hyoglossus.
The Styloglossus, the shortest and smallest of the
three styloid muscles, arises from the anterior and lateral surfaces of
the styloid process, near its apex, and from the stylomandibular ligament.
Passing downward and forward between the internal and external carotid
arteries, it divides upon the side of the tongue near its dorsal surface,
blending with the fibers of the Longitudinalis inferior in front of the
Hyoglossus; the other, oblique, overlaps the Hyoglossus and decussates with its
fibers.
The intrinsic muscles are:
Longitudinalis superior.
Transversus.
Longitudinalis inferior.
Verticalis.
The Longitudinalis
linguæ superior (Superior lingualis) is a thin stratum of
oblique and longitudinal fibers immediately underlying the mucous membrane on
the dorsum of the tongue. It arises from the submucous fibrous layer
close to the epiglottis and from the median fibrous septum, and runs forward to
the edges of the tongue.
Coronal section of tongue, showing intrinsic muscles.
The Longitudinalis linguæ inferior (Inferior
lingualis) is a narrow band situated on the under surface of the tongue
between the Genioglossus and Hyoglossus. It extends from the root to the apex
of the tongue: behind, some of its fibers are connected with the body of the
hyoid bone; in front it blends with the fibers of the Styloglossus.
The Transversus linguæ (Transverse lingualis)
consists of fibers which arise from the median fibrous septum and pass
lateralward to be inserted into the submucous fibrous tissue at the sides of
the tongue.
The Verticalis linguæ (Vertical lingualis)
is found only at the borders of the forepart of the tongue. Its fibers extend
from the upper to the under surface of the organ.
The median fibrous septum of the tongue is very complete, so
that the anastomosis between the two lingual arteries is not very free.
Nerves.—The muscles of the tongue
described above are supplied by the hypoglossal nerve.
Actions.—The movements of the tongue, although
numerous and complicated, may be understood by carefully considering the
direction of the fibers of its muscles. The Genioglossi, by means of their
posterior fibers, draw the root of the tongue forward, and protrude the apex
from the mouth. The anterior fibers draw the tongue back into the mouth. The
two muscles acting in their entirety draw the tongue downward, so as to make
its superior surface concave from side to side, forming a channel along which
fluids may pass toward the pharynx, as in sucking. The Hyoglossi depress the
tongue, and draw down its sides. The Styloglossi draw the tongue upward and
backward. The Glossopalatini draw the root of the tongue upward. The intrinsic
muscles are mainly concerned in altering the shape of the tongue, whereby it
becomes shortened, narrowed, or curved in different directions; thus, the
Longitudinalis superior and inferior tend to shorten the tongue, but the
former, in addition, turn the tip and sides upward so as to render the dorsum
concave, while the latter pull the tip downward and render the dorsum convex.
The Transversus narrows and elongates the tongue, and the Verticalis flattens
and broadens it. The complex arrangement of the muscular fibers of the tongue,
and the various directions in which they run, give to this organ the power of
assuming the forms necessary for the enunciation of the different consonantal
sounds; and Macalister states “there is reason to believe that the musculature
of the tongue varies in different races owing to the hereditary practice and
habitual use of certain motions required for enunciating the several vernacular
languages.”
Structure of the Tongue.—The tongue is
partly invested by mucous membrane and a submucous fibrous layer.
The mucous membrane (tunica mucosa linguæ)
differs in different parts. That covering the under surface of the organ is
thin, smooth, and identical in structure with that lining the rest of the oral
cavity. The mucous membrane of the dorsum of the tongue behind the foramen
cecum and sulcus terminalis is thick and freely movable over the subjacent
parts. It contains a large number of lymphoid follicles, which together
constitute what is sometimes termed the lingual tonsil. Each follicle
forms a rounded eminence, the center of which is perforated by a minute orifice
leading into a funnel-shaped cavity or recess; around this recess are grouped
numerous oval or rounded nodules of lymphoid tissue, each enveloped by a
capsule derived from the submucosa, while opening into the bottom of the
recesses are also seen the ducts of mucous glands. The mucous membrne on the
anterior part of the dorsum of the tongue is thin, intimately adherent to the
muscular tissue, and presents numerous minute surface eminences, the papillæ
of the tongue. It consists of a layer of connective tissue, the corium
or mucosa, covered with epithelium.
The epithelium is of the stratified squamous variety,
similar to but much thinner than that of the skin: and each papilla has a
separate investment from root to summit. The deepest cells may sometimes be
detached as a separate layer, corresponding to the rete mucosum, but they never
contain coloring matter.
The corium consists of a dense felt-work of fibrous
connective tissue, with numerous elastic fibers, firmly connected with the
fibrous tissue forming the septa between the muscular bundles of the tongue. It
contains the ramifications of the numerous vessels and nerves from which the
papillæ are supplied, large plexuses of lymphatic vessels, and the glands
of the tongue.
Structure of the Papillæ.—The papillæ apparently
resemble in structure those of the cutis, consisting of cone-shaped projections
of connective tissue, covered with a thick layer of stratified squamous
epithelium, and containing one or more capillary loops among which nerves are
distributed in great abundance. If the epithelium be removed, it will be found
that they are not simple elevations like the papillæ of the skin, for the
surface of each is studded with minute conical processes which form secondary
papillæ. In the papillæ vallatæ, the nerves are numerous and
of large size; in the papillæ fungiformes they are also numerous, and end
in a plexiform net-work, from which brush-like branches proceed; in the
papillæ filiformes, their mode of termination is uncertain.
Glands of the Tongue.—The tongue is provided
with mucous and serous glands.
The mucous glands are similar in structure to the
labial and buccal glands. They are found especially at the back part behind the
vallate papillæ, but are also present at the apex and marginal parts. In
this connection the anterior lingual glands (Blandin or Nuhn) require special
notice. They are situated on the under surface of the apex of the tongue (Fig. 1013), one on either side of the frenulum, where they are covered by a
fasciculus of muscular fibers derived from the Styloglossus and Longitudinalis
inferior. They are from 12 to
The serous glands occur only at the back of the
tongue in the neighborhood of the taste-buds, their ducts opening for the most
part into the fossæ of the vallate papillæ. These glands are
racemose, the duct of each branching into several minute ducts, which end in
alveoli, lined by a single layer of more or less columnar epithelium. Their
secretion is of a watery nature, and probably assists in the distribution of
the substance to be tasted over the taste area. (Ebner.)
The septum consists of a vertical layer of fibrous
tissue, extending throughout the entire length of the median plane of the
tongue, though not quite reaching the dorsum. It is thicker behind than in front,
and occasionally contains a small fibrocartilage, about
The hyoglossal membrane is a strong fibrous lamina,
which connects the under surface of the root of the tongue to the body of the
hyoid bone. This membrane receives, in front, some of the fibers of the
Genioglossi.
Taste-buds, the end-organs of the gustatory sense,
are scattered over the mucous membrane of the mouth and tongue at irregular
intervals. They occur especially in the sides of the vallate papillæ. In
the rabbit there is a localized area at the side of the base of the tongue, the
papilla foliata, in which they are especially abundant (Fig. 1021). They are described under the organs of the senses (page 991).
Vertical section of papilla foliata of the rabbit, passing across the
folia.
Vessels and Nerves.—The main artery
of the tongue is the lingual branch of the external carotid, but the external maxillary
and ascending pharyngeal also give branches to it. The veins open into
the internal jugular.
The lymphatics of the tongue have been described on
page 696.
The sensory nerves of the tongue are: (1) the lingual
branch of the mandibular, which is distributed to the papillæ at the
forepart and sides of the tongue, and forms the nerve of ordinary sensibility
for its anterior two-thirds; (2) the chorda tympani branch of the facial, which
runs in the sheath of the lingual, and is generally regarded as the nerve of
taste for the anterior two-thirds; this nerve is a continuation of the sensory
root of the facial (nervus intermedius); (3) the lingual branch of the
glossopharyngeal, which is distributed to the mucous membrane at the base and
sides of the tongue, and to the papillæ vallatæ, and which supplies
both gustatory filaments and fibers of general sensation to this region; (4)
the superior laryngeal, which sends some fine branches to the root near the
epiglottis.
The Salivary Glands
—Three large pairs
of salivary glands communicate with the mouth, and pour their secretion into
its cavity; they are the parotid, submandibular, and sublingual.
The
external maxillary artery is imbedded in a grooven in the posterior border of
the gland.