TONGUE

1. Introduction
• The tongue is a muscular organ located on the floor of the mouth.

• It performs five major functions:

1. Taste
2. Speech
3. Chewing (mastication)
4. Swallowing (deglutition)
5. Cleansing of the mouth
• It is made up of skeletal (voluntary) muscles, although in some automatic
actions it may behave involuntarily (e.g., in a classroom situation, as humorously
noted).

2. Parts of the Tongue

The tongue is divided into:

1. Root – Fixed posterior portion.

2. Tip – Anterior free end that lies behind upper incisor teeth when at rest.

3. Body – Divided into:

o Dorsum: Curved upper

surface.

o Inferior surface: Limited to the

oral part.

2.1 Root of Tongue

• Attached superiorly to styloid process
and soft palate.

• Attached inferiorly to mandible and

hyoid bone.

• It is related to geniohyoid and

mylohyoid muscles.

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2.2 Dorsum of Tongue (Fig. 17.1)
• Convex and divided by the sulcus terminalis into:
o Anterior 2/3 (oral part) – Papillary and rough.
o Posterior 1/3 (pharyngeal part) – Smooth and lymphoid.
• At the centre of sulcus terminalis is foramen caecum, a remnant of the
embryonic thyroid diverticulum.

2.3 Inferior Surface of Tongue (Fig. 17.2)

• Smooth mucosa with:
o Frenulum linguae – Median mucosal
fold.
o Deep lingual veins – Lateral to
frenulum.
o Plica fimbriata – Fold lateral to veins,
directed anteromedially.

3. Regions of Tongue
3.1 Oral (Papillary) Part
• Located on the floor of the mouth.
• Lateral margins contact teeth and gums.
• Foliate papillae visible near palatoglossal arch (4–5 vertical folds).
• Dorsum has rough papillae.
• Ventral (inferior) surface is smooth.

3.2 Pharyngeal (Lymphoid) Part

• Located posterior to sulcus terminalis and palatoglossal arch.
• Forms the anterior wall of the oropharynx.
• No papillae; contains lymphoid follicles collectively called the lingual tonsil.

3.3 Posteriormost Part

• Connected to the epiglottis by:
1. Median glossoepiglottic fold
2. Right & left lateral glossoepiglottic folds
• Between folds are depressions called valleculae (Fig. 17.1).
• Lateral folds separate valleculae from the piriform fossae.

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PAPILLAE OF THE TONGUE
These are projections of the mucous membrane (corium) found primarily on the
anterior two-thirds of the tongue. They provide the tongue with its rough texture and
play roles in taste and mechanical handling of food. As described earlier, there are
four main types (see Fig. 17.3):

1. Vallate (Circumvallate) Papillae

o Size: Large (1–2 mm in diameter)

o Number: 8–12

o Location: Just in front of the sulcus terminalis

o Structure: Cylindrical projections surrounded by a circular sulcus

o Function: Taste buds are located in the walls of the papillae

2. Fungiform Papillae
o Location: Tip and margins of the
tongue, also scattered on dorsum

o Size: Smaller than vallate, larger

than filiform

o Appearance: Bright red, with a

narrow stalk and rounded head

o Function: Contain taste buds

3. Filiform Papillae
o Most numerous and smallest

o Location: Presulcal area of dorsum

o Appearance: Pointed, keratinized, often split at tip

o Function: Do not contain taste buds; provide mechanical grip to food

o Give the tongue a velvety texture

4. Foliate Papillae
o Location: Lateral margins, just anterior to vallate papillae

o Shape: Leaf-like folds

o Function: In humans, taste function is reduced compared to animals

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MUSCLES OF THE TONGUE
The tongue has a midline fibrous septum that divides it into right and left halves. Each
half contains:

• 4 Intrinsic muscles → alter the shape of the tongue

• 4 Extrinsic muscles → move the tongue as a whole

Intrinsic Muscles (Fig. 17.4)

These muscles do not attach to bone. They are responsible for changing the shape of
the tongue (e.g., curling, narrowing, broadening).

1. Superior Longitudinal Muscle

o Origin: Fibrous tissue deep
to mucosa on dorsum
o Course: From tip to root of
tongue
o Insertion: Mucous
membrane
o Action: Elevates tip and
sides → shortens the tongue,
forms a concave dorsum
2. Inferior Longitudinal Muscle

o Origin: Beneath mucosa

from tip to hyoid bone
o Course: Runs along underside of tongue
o Location: Between genioglossus and hyoglossus
o Action: Curls tip downwards, makes dorsum convex, also shortens the
tongue
3. Transverse Muscle
o Location: Beneath superior longitudinal, superficial to genioglossus
o Course: From midline septum to lateral margins
o Action: Narrows and thickens the tongue
4. Vertical Muscle
o Location: Borders of anterior tongue

o Action: Flattens and broadens the tongue

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Extrinsic Muscles
These muscles attach the tongue to surrounding structures and are responsible for

Table 17.2: Summary of Actions of Tongue Muscles

Intrinsic Muscles

Muscle Action

Superior longitudinal Shortens tongue; makes dorsum concave

Inferior longitudinal Shortens tongue; makes dorsum convex

Transverse Narrows and elongates the tongue

Vertical Broadens and flattens the tongue

Extrinsic Muscles

Muscle Action

Genioglossus Protrudes tongue; pulls posterior part forward; life-saving role

Hyoglossus Depresses tongue; retracts protruded tongue

Styloglossus Pulls tongue upward and backward (retracts)

Palatoglossus Elevates tongue; closes oropharyngeal isthmus

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ARTERIAL SUPPLY OF THE TONGUE
1. Main Artery:
The lingual artery, a branch of the external carotid artery, is the main blood
supply to the tongue. It is tortuous in course to allow free tongue movements.

2. Additional Arterial Supply to the Root:

o The tonsillar branch of the facial artery

o The ascending pharyngeal artery, another branch of the external

carotid artery

VENOUS DRAINAGE OF THE TONGUE

1. Deep Lingual Vein:
This is the main vein of the tongue, visible on the underside (inferior surface) of
the tongue near the midline.
2. Venae Comitantes of the Lingual Artery:
These veins run alongside the lingual artery and are joined by the dorsal lingual
veins.
3. Venae Comitantes of the Hypoglossal Nerve:
These accompany the hypoglossal nerve and eventually unite with the above
veins.
4. Final Drainage:
All the above veins join together at the posterior border of the hyoglossus muscle
to form the lingual vein, which then drains into the internal jugular vein.

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LYMPHATIC DRAINAGE OF THE TONGUE
1. Tip of the Tongue:
Drains bilaterally to the submental lymph nodes.
See Figs. 17.7a and 17.7b.

2. Anterior Two-Thirds (Except Tip):

Drains unilaterally into submandibular lymph nodes.
Some central lymphatics also drain bilaterally into deep cervical lymph nodes.

3. Posterior One-Third and Posteriormost Part:

Drains bilaterally into the upper deep cervical nodes, especially the
jugulodigastric nodes.

4. Final Drainage:
All lymph from the tongue eventually reaches the jugulo-omohyoid nodes, also
known as the lymph nodes of the tongue.

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NERVE SUPPLY OF THE TONGUE
Motor Nerve Supply (Muscle Control)

1. Main Motor Nerve:

o All intrinsic and extrinsic muscles
of the tongue (except one) are
supplied by the hypoglossal
nerve (Cranial Nerve XII).

2. Exception - Palatoglossus Muscle:

o Supplied by the cranial root of
the accessory nerve (XI) via the
pharyngeal plexus.

So, 7 out of 8 tongue muscles are supplied

by the hypoglossal nerve.

Sensory Nerve Supply (Touch, Pain, and Taste)

Region of Tongue General Sensation Taste

Chorda tympani (branch of CN
Anterior 2/3 Lingual nerve (branch of CN V3)
VII)
Glossopharyngeal nerve (CN
Posterior 1/3 Glossopharyngeal nerve (CN IX)
IX)
Posterior-most Vagus nerve via internal laryngeal
Vagus nerve via same branch
part branch

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HYPOGLOSSAL NERVE (XII Cranial Nerve)
It is the main motor nerve of the tongue muscles.
1. Origin and Exit from Skull:
• The hypoglossal nerve arises from the medulla oblongata of the brainstem.
• It exits the cranial cavity through the hypoglossal canal, also called the
anterior condylar canal.
2. Course of the Nerve:
a. In the Neck (Initial Pathway):
• After exiting the skull, the nerve lies between the:
o Internal jugular vein (laterally) and
o Internal carotid artery (medially).
• At this point, it is positioned anterior to the vagus nerve (X).
b. Lower in the Neck:
• The nerve curves forwards and downwards.
• It crosses both:
o The internal carotid artery
o And the external carotid artery
c. Before Entering the Tongue:
• It also crosses the loop of the lingual artery (which is tortuous).
• Then, it lies on the surface of the hyoglossus muscle.
d. Final Destination:
• From the hyoglossus, it enters the substance of the tongue to supply its
muscles.
3. Muscles Supplied:
a. Extrinsic Muscles Supplied:
• Genioglossus
• Hyoglossus
• Styloglossus
b. Intrinsic Muscles Supplied:
• Superior longitudinal
• Inferior longitudinal
• Transverse
• Vertical
In total, the hypoglossal nerve supplies 7 out of the 8 tongue muscles.
The only exception is the palatoglossus, which is supplied by the cranial root of
the accessory nerve (via pharyngeal plexus).

For further anatomical details, refer to Chapter 4 of BD Chaurasia’s Human Anatomy, Volume 4.

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 CLINICAL ANATOMY OF THE TONGUE
1. Carcinoma of the Tongue
• Carcinoma (cancer) of the tongue is fairly common, especially in tobacco
users.
• During treatment, the affected side of the tongue is surgically removed.
• Because cancer cells often spread to deep cervical lymph nodes, a block
dissection of the neck (removal of all lymph nodes) is done.
• Posterior one-third (pharyngeal part) of the tongue is more dangerous when
involved in cancer because:
o It has bilateral lymphatic drainage.
o This increases the risk of recurrence and spread.

2. Sublingual Administration of Sorbitrate

• Sorbitrate (Isosorbide dinitrate) is used in angina pectoris (chest pain due to
reduced blood flow to heart).
• It is placed under the tongue (sublingual).
• This route is very effective because:
o The tongue has a rich blood supply, so the drug is absorbed very
quickly.
o It bypasses the liver (portal circulation), giving faster action.

3. Genioglossus: The ‘Safety Muscle’ of the Tongue

• The genioglossus muscle helps protrude (push forward) the tongue.
• It is known as the “safety muscle” because:
o If it gets paralysed, the tongue falls backward, especially during
unconsciousness or anaesthesia.
o This can block the airway, causing respiratory obstruction.
o Therefore, during general anaesthesia, the tongue is often pulled
forward to prevent airway blockage.

4. Clinical Test for Hypoglossal Nerve (XII Cranial Nerve)

• The genioglossus is the only muscle that protrudes the tongue.
• It is used to test the function of the hypoglossal nerve.
• If the right hypoglossal nerve is damaged:
o The right genioglossus is paralysed.
o The left genioglossus pulls the base of the tongue to the left, so the tip
(apex) of the tongue deviates to the right.
o (Remember: base and apex lie in opposite directions.)
• This is seen during tongue protrusion (refer Fig. 17.9 for visual reference).

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HISTOLOGY OF THE TONGUE

1. Muscle Composition
• The bulk of the tongue is made up of striated (skeletal) muscle fibers, allowing
voluntary movement.
2. Mucous Membrane
• Lined by stratified squamous epithelium with a connective tissue layer
beneath (called corium).
• Different surfaces of the tongue have different characteristics:
o Oral part of dorsum: Thin, tightly adherent, forms papillae (see Fig.
17.3).
o Pharyngeal part of dorsum: Contains numerous lymphoid follicles
(forms lingual tonsil).
o Inferior surface: Thin, smooth mucosa.
• Below the mucosa, mucous and serous glands are found.
3. Taste Buds
• Located in:
o Sides of circumvallate papillae and their sulci
o Foliate papillae
o Posterior one-third of the tongue
o Sparsely on: Fungiform papillae, soft palate, epiglottis, and pharynx
• Absent in the mid-dorsal area of anterior tongue (oral part) (see Fig. 17.10).
4. Cell Types in Taste Buds
• Sustentacular cells: Supporting, spindle-shaped.
• Gustatory cells: Long, slender, centrally located; responsible for taste
perception.

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DEVELOPMENT OF THE TONGUE

A. Epithelium (Derived from Endoderm)

Region Embryological Origin Nerve Supply
- Lingual nerve (general
sensation, post-trematic of 1st
From two lingual swellings of
Anterior 2/3 arch)
the 1st branchial arch
- Chorda tympani (taste, pre-
trematic of 2nd arch)
From cranial part of
Glossopharyngeal nerve
Posterior 1/3 hypobranchial eminence, i.e.
(general sensation and taste)
3rd arch
Posteriormost part Internal laryngeal branch of
From 4th arch
& vallecula vagus nerve

Note: The vallate papillae, although located in the anterior 2/3, develop from the
posterior part and are innervated by the glossopharyngeal nerve.

B. Muscle Development
• Muscles of the tongue originate from occipital myotomes (somites).
• These migrate into the tongue and are supplied by the hypoglossal nerve
(cranial nerve XII).
• Exception: Palatoglossus, derived from the mesoderm of the 6th arch, is
supplied by the cranial root of the accessory nerve via the pharyngeal plexus.

TABLE 17.3: COMPARISON OF THE PARTS OF THE TONGUE

Feature Anterior 2/3 Posterior 1/3 Posteriormost Part
Lies in the mouth Lies in the
Location Lies in the oropharynx
cavity oropharynx
Contains lymphoid
Structure Has papillae ---
tissue
Function Chewing and speech Swallowing (deglutition) Swallowing
General
Lingual nerve (post- Glossopharyngeal Internal laryngeal
Sensory
trematic of 1st arch) nerve nerve (vagus)
Nerve
Glossopharyngeal
Chorda tympani Internal laryngeal
Taste Nerve (includes vallate
(except vallate papillae) nerve
papillae)

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 Feature Anterior 2/3 Posterior 1/3 Posteriormost Part
From 4th arch
From lingual swellings From 3rd arch which which forms small
Development of 1st arch (tuberculum forms large part of dorsal part of
impar disappears) hypobranchial eminence hypobranchial
eminence
All tongue muscles
(except palatoglossus) Palatoglossus from 6th
arise from occipital arch, supplied by
Muscle Origin —
myotomes and are cranial accessory via
supplied by pharyngeal plexus
hypoglossal nerve (XII)

CONNECTIVE TISSUE OF THE TONGUE

• The connective tissue in the tongue develops from local mesenchyme
(embryonic connective tissue).
• This connective tissue forms the supportive framework beneath the mucous
membrane and around muscles and glands.
TASTE PATHWAY
Taste sensations from different parts of the tongue travel through specific nerves to the
brain:
1. Anterior Two-Thirds of Tongue (except vallate papillae)
• Taste carried by the chorda tympani branch of the facial nerve (cranial nerve
VII).
• The taste fibers travel to the geniculate ganglion.
• From there, the central fibers go to the tractus solitarius in the medulla
oblongata (brainstem).
2. Posterior One-Third of Tongue (including circumvallate papillae)
• Taste carried by the glossopharyngeal nerve (cranial nerve IX).
• Fibers reach the inferior (petrosal) ganglion of CN IX.
• Central processes also project to the tractus solitarius in the medulla.
3. Posteriormost Part of Tongue and Epiglottis
• Taste carried by the vagus nerve (cranial nerve X).
• Fibers go to the inferior ganglion of vagus nerve.
• Central fibers also terminate in the tractus solitarius.
4. From Tractus Solitarius to Cortex
• After synapsing in the tractus solitarius, second-order neurons form the
solitariothalamic tract.
• This tract joins the trigeminal lemniscus pathway.

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 • It projects to the posteroventromedial nucleus of the thalamus on the
opposite side.
• Third-order neurons carry taste sensation to the lowest part of the postcentral
gyrus (primary gustatory cortex), where taste is consciously perceived.
(See Fig. 17.12 for pathway illustration)

CLINICAL ANATOMY
• Injury to any part of the taste pathway (from tongue to brain) causes loss or
distortion of taste sensation.
• Referred pain example:
o Diseases affecting the posterior part of the tongue often cause
referred pain to the ear.
o This occurs because cranial nerves IX (glossopharyngeal) and X
(vagus) supply both the tongue's posterior part and the ear.
• Other referred pain patterns related to cranial nerve distributions are
demonstrated in Fig. 17.13.

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