4. • The tongue is a muscular organ situated
in the floor of the mouth.
• It has an oral part which lies in the mouth,
and a pharyngeal part that lies in the
pharynx.
• Oral and pharyngeal parts are separated
by a V-shaped sulcus called sulcus
terminalis.
• The tongue is anchored to the floor of
the mouth by the lingual frenum.
6. Speech
• Speech is the product of air leaving the lungs
via the mouth.
• The tongue is responsible for different sounds
depending on how it's positioned in the mouth.
• Since the tongue is so flexible, it can switch
positions quickly to make a rapid succession of
sounds.
7. Taste
• Taste buds are responsible for the ability to taste
food.
• There are five different taste sensations: sweet,
sour, salty, bitter and savory, according to the
National Institute on Deafness and Other
Communication Disorders.
• Taste buds for each of the five sensations are
scattered along the tongue's surface, rather than
localized in specific sections.
• All tastes are perceived everywhere.
8. Mastication
• Mastication is the process of combining
ground up food particles with naturally
occurring saliva.
• Mastication happens at the same time as
grinding.
• Grinding is when teeth convert large food
particles into small ones.
• The tongue first positions food between the
teeth for chewing before mixing it with saliva.
9. Deglutition
• After masticating food particles, the tongue
helps round them into masses known as bolus.
• Once the bolus is formed, the tongue pushes
them toward the esophagus found in the back
of the mouth before finding its way to the
stomach for digestion.
11. Basic Overview
• The tongue is divided into two parts: oral part (anterior two third) and pharyngeal part
(posterior one-third).
• The oral part of tongue develops from three swellings associated with first pharyngeal
arch.These swellings are two lateral lingual swellings and one median swelling—the
tuberculum impar.
• The pharyngeal part of tongue develops from a median swelling called hypobranchial
eminence or copula of His associated with second, third, and fourth pharyngeal arches.
• Muscles of tongue develop from occipital myotomes.
12. Stages of
Development
A. At 4 weeks.
B. Late in the fifth week.
C. Early in the sixth week.
D. Middle of the seventh week.
E. Adult
14. INITIAL DEVELOPMENT
The tongue develops in the floor of
developing mouth from first, second, third, and
fourth pharyngeal arches. At the end of the fourth
week of intrauterine life (IUL), a small median
triangular swelling called tuberculum impar
develops in the floor of primitive pharynx, just
cranial to foramen cecum.
Soon after the appearance of tuberculum
impar the two lateral oval swellings called lingual
swellings develop one on each side of tuberculum
impar. The two lateral lingual swellings are placed
slightly distal to the tuberculum impar, hence they
are also called distal tongue buds.
15. INITIAL DEVELOPMENT
Caudal to tubercular impar a second large
median swelling called hypobranchial eminence
(copula of His) develops in the floor of primitive
pharynx in relation to second, third, and fourth
pharyngeal arches. The hypobranchial eminence
soon subdivides into large cranial part and small
caudal part.
18. • The two lateral lingual swellings overgrow the
tuberculum impar and merge with each other
to form anterior two-third of the tongue.
• The line of fusion of two lingual swellings in the
median plane forms median sulcus on the
dorsal surface of the tongue.
• The tuberculum impar does not form any
recognizable part of the adult tongue.
• Since mucous membrane covering the anterior
two-third of the tongue develops from the first
pharyngeal arch, it is innervated by mandibular
branch of trigeminal nerve—the nerve of first
arch.
19. • The posterior one-third of the tongue
including circumvallate papillae develops from
cranial part of hypobranchial eminence.
• The line of fusion of the anterior two-third and
posterior one-third of the tongue is indicated by
aV-shaped groove—the sulcus terminalis.
• Since the mucous membrane of the posterior
one-third of tongue (including vallate papillae)
develops from the third pharyngeal arch, it is
supplied by glossopharyngeal nerve—the nerve
of third arch.
20. • The posterior most part of the tongue and
epiglottis develop from the caudal part of the
hypobranchial eminence.
• Since the mucous membrane of the posterior
most part of tongue and epiglottis develop from
fourth pharyngeal arch, it is supplied by the
superior laryngeal nerve—the nerve of the
fourth arch.
21. During this sequence of
events, the third arch mesoderm
grows over the mesoderm of the
second arch and fuses with the
mesoderm of the first arch. Thus,
second arch gets buried
underneath the third arch and
thereby gets excluded from the
tongue development.
23. The muscles of tongue develop from
myoblasts that migrate into developing tongue
from the occipital myotomes. The hypoglossal
nerve, the nerve of occipital myotomes,
accompanies the myoblasts during their migration
to the pharyngeal arches and innervates the
muscles of tongue as they develop. The migration
of the occipital myotomes to the developing
tongue explains the course of the hypoglossal
nerve. Some muscles of tongue probably develop
in situ.
24. 1. Mucous membrane of the tongue is derived
from the endoderm of the primitive foregut.
2. Taste buds are formed in relation to the
terminal branches of nerves carrying taste
sensations.
3. Muscles of the tongue develop from occipital
myotomes.
4. Fibro-areolar tissue that binds the tongue
muscles develops from mesenchyme of the
pharyngeal arches.
25. Relation of Anterior Part
of Tongue with the Floor
of the Mouth
In the region of floor of the mouth,
mandibular process forms three
structures: (a) lower lip and lower parts
of cheeks, (b) lower jaw, and (c) tongue.
At first these structures are not
discernible from each other. Soon the
tongue forms a recognizable swelling in
the middle. A sulcus called
linguogingival sulcus develops on
either side of this swelling and
separates the developing tongue from
the floor of the mouth.
29. References
1. Vishram Singh. Development of Tongue and Thyroid. Textbook of Clinical
Embryology. New Delhi: Elsevier; 2012. p. 122 – 125.
2. Inderbir Singh. Alimentary System – I: Mouth, Pharynx and Related Structures. In: V
Subhadra Devi, editor. Human Embryology. Eleventh Edition. New Delhi: Jaypee
Brothers Medical Publishers (P) Ltd; 2018. p. 168 – 170.
3. Sadler TW, Head and Neck. System-Based Embryology. In: Crystal Taylor, Andrea
Vosburgh, editors. Langman’s Medical Embryology. Fourteenth Edition. Philadelphia:
Wolters Kluwer; 2019. p. 298 – 299.
4. Schoenwolf, Bleyl, Brauer, Francis-west. Development of the Pharyngeal Apparatus
and Face. Larsen’s Human Embryology. Fifth Edition. Philadelphia: Elsevier: 2015. p.
458 – 451.
