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.

Overview

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 9 metres long, extending from the mouth to the anus, and lined throughout its entire extent by mucous membrane. It has received different names in the various parts of its course: at its commencement is the mouth, where provision is made for the mechanical division of the food (mastication), and for its admixture with a fluid secreted by the salivary glands (insalivation); beyond this are the organs of deglutition, the pharynx and the esophagus, which convey the food into the stomach, in which it is stored for a time and in which also the first stages of the digestive process take place; the stomach is followed by the small intestine, which is divided for purposes of description into three parts, the duodenum, the jejunum, and ileum. In the small intestine the process of digestion is completed and the resulting products are absorbed into the blood and lacteal vessels. Finally the small intestine ends in the large intestine, which is made up of cecum, colon, rectum, and anal canal, the last terminating on the surface of the body at the anus.

  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.

 

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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.

 

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Head end of human embryo of about thirty to thirty-one days.

 

 

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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.

 

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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.

 

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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.

 

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Front view of two successive stages in the development of the digestive tube.

 

 

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The primitive mesentery of a six weeks’ human embryo, half schematic.

 

 

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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.

 

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Reconstruction of a human embryo of 17 mm.

 

  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 .

 

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Diagrams to illustrate two stages in the development of the digestive tube and its mesentery. The arrow indicates the entrance to the bursa omentalis.

 

 

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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

 

 

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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.

 

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FIG. 990– Diagrams to illustrate the development of the greater omentum and transverse mesocolon. (See enlarged image)

 

 

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Tail end of human embryo from fifteen to eighteen days old.

 

 

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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

 

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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.

Upper and lower lips (labia) formed by orbicularis oris muscle covered externally by skin and internally by mucous membrane and surround the mouth are the entrance to the oral cavity. Both lips unite laterally by labial commissure. Around the oral vestibule and between the mucous membrane and the orbicularis oris muscle are located labial salivary glands. The ducts of these small glands open into the vestibule. The upper and lower lips are attached to the gingivae in the median plane by raised folds of mucous membrane, called the superior and inferior labial frenula. The upper lip has a median vertical groove called the philtrum. Intermediate portion red area located between the skin and the mucous membrane.

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.

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Permanent teeth of upper dental arch, seen from below.

 

 

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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.

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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).

 

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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 2 mm in diameter). They lie just anterior to the sulcus terminalis and carry taste buds.

·            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 2.5 cm. from the root of the organ, in a depression, the foramen cecum, from which a shallow groove, the sulcus terminalis, runs lateralward and forward on either side to the margin of the tongue. The part of the dorsum of the tongue in front of this groove, forming about two-thirds of its surface, looks upward, and is rough and covered with papillæ; the posterior third looks backward, and is smoother, and contains numerous muciparous glands and lymph follicles (lingual tonsil). The foramen cecum is the remains of the upper part of the thyroglossal duct or diverticulum from which the thyroid gland is developed; the pyramidal lobe of the thyroid gland indicates the position of the lower part of the duct.

  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.

 

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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 2 mm. wide, attached to the bottom of a circular depression of the mucous membrane; the margin of the depression is elevated to form a wall (vallum), and between this and the papilla is a circular sulcus termed the fossa. The papilla is shaped like a truncated cone, the smaller end being directed downward and attached to the tongue, the broader part or base projecting a little above the surface of the tongue and being studded with numerous small secondary papillæ and covered by stratified squamous epithelium.

  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.

Glossopalatinus. 

 

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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 2 cm. long, and arises from the medial side and base of the lesser cornu and contiguous portion of the body of the hyoid bone, and passes directly upward to blend with the intrinsic muscular fibers of the tongue, between the Hyoglossus and Genioglossus.

  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.

 

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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 25 mm. long, and about 8 mm. broad, and each opens by three or four ducts on the under surface of the apex.

  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 6 mm. in length. It is well displayed by making a vertical section across the organ.

  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).

 

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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.

 

Parotid Gland (glandula parotis).—The parotid gland, the largest of the three, varies in weight from 14 to 28 gm. It lies upon the side of the face, immediately below and in front of the external ear. The main portion of the gland is superficial, somewhat flattened and quadrilateral in form, and is placed between the ramus of the mandible in front and the mastoid process and Sternocleidomastoideus behind, overlapping, however, both boundaries. Above, it is broad and reaches nearly to the zygomatic arch; below, it tapers somewhat to about the level of a line joining the tip of the mastoid process to the angle of the mandible. The remainder of the gland is irregularly wedge-shaped, and extends deeply inward toward the pharyngeal wall.

Structures within the Gland.—The external carotid artery lies at first on the deep surface, and then in the substance of the gland. The artery gives off its posterior auricular branch which emerges from the gland behind; it then divides into its terminal branches, the internal maxillary and superficial temporal; the former runs forward deep to the neck of the mandible; the latter runs upward across the zygomatic arch and gives off its transverse facial branch which emerges from the front of the gland. Superficial to the arteries are the superficial temporal and internal maxillary veins, uniting to form the posterior facial vein; in the lower part of the gland this vein splits into anterior and posterior divisions. The anterior division emerges from the gland and unites with the anterior facial to form the common facial vein; the posterior unites in the gland with the posterior auricular to form the external jugular vein. On a still more superficial plane is the facial nerve, the branches of which emerge from the borders of the gland. Branches of the great auricular nerve pierce the gland to join the facial, while the auriculotemporal nerve issues from the upper part of the gland.

  The parotid duct (ductus parotideus; Stensen’s duct) is about 7 cm. long. It begins by numerous branches from the anterior part of the gland, crosses the Masseter, and at the anterior border of this muscle turns inward nearly at a right angle, passes through the corpus adiposum of the cheek and pierces the Buccinator; it then runs for a short distance obliquely forward between the Buccinator and mucous membrane of the mouth, and opens upon the oral surface of the cheek by a small orifice, opposite the second upper molar tooth. While crossing the Masseter, it receives the duct of the accessory portion; in this position it lies between the branches of the facial nerve; the accessory part of the gland and the transverse facial artery are above it.

 

Structure.—The parotid duct is dense, its wall being of considerable thickness; its canal is about the size of a crow-quill, but at its orifice on the oral surface of the cheek its lumen is greatly reduced in size. It consists of a thick external fibrous coat which contains contractile fibers, and of an internal or mucous coat lined with short columnar epithelium.

 

Vessels and Nerves.—The arteries supplying the parotid gland are derived from the external carotid, and from the branches given off by that vessel in or near its substance. The veins empty themselves into the external jugular, through some of its tributaries. The lymphatics end in the superficial and deep cervical lymph glands, passing in their course through two or three glands, placed on the surface and in the substance of the parotid. The nerves are derived from the plexus of the sympathetic on the external carotid artery, the facial, the auriculotemporal, and the great auricular nerves. It is probable that the branch from the auriculotemporal nerve is derived from the glossopharyngeal through the otic ganglion. At all events, in some of the lower animals this has been proved experimentally to be the case.

 

Submandibular Gland (glandula submandibularis).—The submandibular gland is irregular in form and about the size of a walnut. A considerable part of it is situated in the submandibular triangle, reaching forward to the anterior belly of the Digastricus and backward to the stylomandibular ligament, which intervenes between it and the parotid gland. Above, it extends under cover of the body of the mandible; below, it usually overlaps the intermediate tendon of the Digastricus and the insertion of the Stylohyoideus, while from its deep surface a tongue-like deep process extends forward above the Mylohyoideus muscle.

  Its superficial surface consists of an upper and a lower part. The upper part is directed outward, and lies partly against the submandibular depression on the inner surface of the body of the mandible, and partly on the Pterygoideus internus. The lower part is directed downward and outward, and is covered by the skin, superficial fascia, Platysma, and deep cervical fascia; it is crossed by the anterior facial vein and by filaments of the facial nerve; in contact with it, near the mandible, are the submandibular lymph glands.

 

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 Dissection, showing salivary glands of right side.   D:\konspekt\gray\henry gray anatomy\www.bartleby.com\107\illus1024.html

 

  The deep surface is in relation with the Mylohyoideus, Hyoglossus, Styloglossus, Stylohyoideus, and posterior belly of the Digastricus; in contact with it are the mylohyoid nerve and the mylohyoid and submental vessels.

  The external maxillary artery is imbedded in a grooven in the posterior border of the gland.

  The deep process of the gland extends forward between the Mylohyoideus below and externally, and the Hyoglossus and Styloglossus internally; above it is the lingual nerve and submandibular ganglion; below it the hypoglossal nerve and its accompanying vein.

  The submandibular duct (ductus submandibularis; Wharton’s duct) is about 5 cm. long, and its wall is much thinner than that of the parotid duct. It begins by numerous branches from the deep surface of the gland, and runs forward between the Mylohyoideus and the Hyoglossus and Genioglossus, then between the sublingual gland and the Genioglossus, and opens by a narrow orifice on the summit of a small papilla, at the side of the frenulum linguæ. On the Hyoglossus it lies between the lingual and hypoglossal nerves, but at the anterior border of the muscle it is crossed laterally by the lingual nerve; the terminal branches of the lingual nerve ascend on its medial side.

 

Vessels and Nerves.—The arteries supplying the submandibular gland are branches of the external maxillary and lingual. Its veins follow the course of the arteries. The nerves are derived from the submandibular ganglion, through which it receives filaments from the chorda tympani of the facial nerve and the lingual branch of the mandibular, sometimes from the mylohyoid branch of the inferior alveolar, and from the sympathetic.

 

Sublingual Gland (glandula sublingualis).—The sublingual gland is the smallest of the three glands. It is situated beneath the mucous membrane of the floor of the mouth, at the side of the frenulum linguæ, in contact with the sublingual depression on the inner surface of the mandible, close to the symphysis. It is narrow, flattened, shaped somewhat like an almond, and weighs nearly 2 gm. It is in relation, above, with the mucous membrane; below, with the Mylohyoideus; behind, with the deep part of the submandibular gland; laterally, with the mandible; and medially, with the Genioglossus, from which it is separated by the lingual nerve and the submandibular duct. Its excretory ducts are from eight to twenty in number. Of the smaller sublingual ducts (ducts of Rivinus), some join the submandibular duct; others open separately into the mouth, on the elevated crest of mucous membrane (plica sublingualis), caused by the projection of the gland, on either side of the frenulum linguæ. One or more join to form the larger sublingual duct (duct of Bartholin), which opens into the submandibular duct.

 

Vessels and Nerves.—The sublingual gland is supplied with blood from the sublingual and submental arteries. Its nerves are derived from the lingual, the chorda tympani, and the sympathetic.

 

Structure of the Salivary Glands.—The salivary glands are compound racemose glands, consisting of numerous lobes, which are made up of smaller lobules, connected together by dense areolar tissue, vessels, and ducts. Each lobule consists of the ramifications of a single duct, the branches ending in dilated ends or alveoli on which the capillaries are distributed. The alveoli are enclosed by a basement membrane, which is continuous with the membrana propria of the duct and consists of a net-work of branched and flattened nucleated cells.

  The alveoli of the salivary glands are of two kinds, which differ in the appearance of their secreting cells, in their size, and in the nature of their secretion. (1) The mucous variety secretes a viscid fluid, which contains mucin; (2) the serous variety secretes a thinner and more watery fluid. The sublingual gland consists of mucous, the parotid of serous alveoli. The submandibular contains both mucous and serous alveoli, the latter, however, preponderating.

  The cells in the mucous alveoli are columnar in shape. In the fresh condition they contain large granules of mucinogen. In hardened preparations a delicate protoplasmic net-work is seen, and the cells are clear and transparent. The nucleus is usually situated near the basement membrane, and is flattened.

  In some alveoli are seen peculiar crescentic bodies, lying between the cells and the membrana propria. They are termed the crescents of Gianuzzi, or the demilunes of Heidenhainm and are composed of polyhedral granular cells, which Heidenhain regards as young epithelial cells destined to supply the place of those salivary cells which have undergone disintegration. This view, however, is not accepted by Klein. Fine canaliculi pass between the mucus-secreting cells to reach the demilunes and even penetrate the cells forming these structures.

  In the serous alveoli the cells almost completely fill the cavity, so that there is hardly any lumen perceptible; they contain secretory granules imbedded in a closely reticulated protoplasm. The cells are more cubical than those of the mucous type; the nucleus of each is spherical and placed near the center of the cell, and the granules are smaller.

  Both mucous and serous cells vary in appearance according to whether the gland is in a resting condition or has been recently active. In the former case the cells are large and contain many secretory granules; in the latter case they are shrunken and contain few granules, chiefly collected at the inner ends of the cells. The granules are best seen in fresh preparations.

  The ducts are lined at their origins by epithelium which differs little from the pavement form. As the ducts enlarge, the epithelial cells change to the columnar type, and the part of the cell next the basement membrane is finely striated.

  The lobules of the salivary glands are richly supplied with bloodvessels which form a dense net-work in the interalveolar spaces. Fine plexuses of nerves are also found in the interlobular tissue. The nerve fibrils pierce the basement membrane of the alveoli, and end in branched varicose filaments between the secreting cells. In the hilus of the submandibular gland there is a collection of nerve cells termed Langley’s ganglion.

Accessory Glands.—Besides the salivary glands proper, numerous other glands are found in the mouth. Many of these glands are found at the posterior part of the dorsum of the tongue behind the vallate papillæ, and also along its margins as far forward as the apex. Others lie around and in the palatine tonsil between its crypts, and large numbers are present in the soft palate, the lips, and cheeks. These glands are of the same structure as the larger salivary glands, and are of the mucous or mixed type.

Salivary glands may be subdivided into small and large. Small one (labial, buccal, palatine and lingual) situated in mucous membrane of mouth cavity.

Parotid gland is situated in retromandibular fossa: front and lower from auricle, laterally from ramus mandibulae and posterior margin of masseter muscle. This is – compound alveolar gland, which produces serous secret. Parotid duct opens on the cheeks into vestibule of mouth cavity opposite the second superior molar. Parotid gland has superficial part and deep part also can be additional parotid gland, which disposes on surface of masticator muscle closely to parotid duct.

Submandibular gland lies in submandibular triangle, it is compound alveolar-tubular gland, and produces mixed secret. Submandibular duct (Vartona) opens on sublingual papilla.

Sublingual gland lies in the floor of the mouth between the mandible and the genioglossus muscle. This is compound alveolar-tubular gland, it produces mucous secret. Greater sublingual duct opens on sublingual papilla near submandibular duct (sometimes the ducts open together as one). Lesser sublingual ducts open along sublingual fold.

 

Prepared by

Reminetskyy B.Y.