The head and neck region of four week human embryo somewhat resemble these regions of a fish embryo of comparable stage This explains the former use of designation branchial apparatus Branchial is derived from the Greek word branchia or gill

1. Dr. NDAYISABA CORNEILLE
CEO of CHG
MBChB,DCM,BCSIT,CCNA
THE EMBRYOLOGY OF
HEAD & NECK
Supported BY

2. Pharyngeal Apparatus
• The head and neck region of four week human
embryo somewhat resemble these regions of a
fish embryo of comparable stage
• This explains the former use of designation
branchial apparatus
• Branchial is derived from the Greek word
branchia or gill
Dr Ndayisaba Corneille

3. Pharyngeal Apparatus
Pharyngeal apparatus consists of:
• Pharyngeal arches
• Pharyngeal pouches
• Pharyngeal grooves
• Pharyngeal membrane
Dr Ndayisaba Corneille

4. • Pharyngeal arches are cylindrical mesodermal bars
covered by ectoderm and lined internally by the
endoderm
• Appears in 4th and 5th week of development
• Number-6 pairs of pharyngeal arches of which 5th
arch disappears early living no important remnants
Dr Ndayisaba Corneille

5. Dr Ndayisaba Corneille

6. Dr Ndayisaba Corneille

7. Pharyngeal Arches
• By the end of the fourth week, four pairs of
pharyngeal arches are visible externally
• The fifth and sixth arches are rudimentary and are not
visible on the surface of the embryo
• The pharyngeal arches are separated from each other
by fissures called pharyngeal grooves
• They are numbered in craniocaudal sequence
Dr Ndayisaba Corneille

8. Pharyngeal Arch Components
• Each pharyngeal arch consists of a core of
mesenchyme
• Is covered externally by ectoderm and internally by
endoderm
• In the third week the original mesenchyme is derived
from mesoderm
• During the fourth week most of the mesenchyme is
derived from neural crest cells that migrate into the
pharyngeal arches Dr Ndayisaba Corneille

9. Fate of Pharyngeal Arches
• The pharyngeal arches contribute exclusively to the
formation the face, nasal cavities, mouth, larynx,
pharynx and neck
• During the fifth week, the second pharyngeal arch
enlarges and overgrows the third and fourth arches,
forming the ectodermal depression called cervical
sinus
• By the end of seventh week the second to fourth
pharyngeal grooves and the cervical sinus have
disappeared, giving the neck a smooth contour
Dr Ndayisaba Corneille

10. Dr Ndayisaba Corneille

11. Fate of Pharyngeal Arches
A typical pharyngeal arch contains:
• An aortic arch, an artery that arises from the truncus arteriosus
of the primordial heart
• A cartilaginous rod that forms the skeleton of the arch
• A muscular component that differentiates into muscles in the
head and neck
• A nerve that supplies the mucosa and muscles derived from
the arch
Dr Ndayisaba Corneille

12. Mesenchyme of pharyngeal arch:
• Original : Paraxial and lateral plate
- gives rise to musculature of face and neck
• Neural crest cells – source of connective
tissue components including bones,
cartilages, ligaments in oral and facial
region.
Dr Ndayisaba Corneille

13. Derivatives of the Mesodermal pharyngeal arches
• Skeletal elements
• Muscular elements
• Arteries
• Nerves
Dr Ndayisaba Corneille

14. Skeletal elements
First arch/mandibular arch:
It is differentiated into dorsal
maxillary process and ventral
mandibular part.
• Maxillary process forms
Premaxilla, maxilla,zygomatic
bone, Squamous part of
temporal bone.
• The cartilaginous bar of
mandibular part is known as
Meckel’s cartilage.
• Dorsal part of cartilage is
ossified to form malleus and
incus.
Dr Ndayisaba Corneille

15. • Succeeding part of the
cartilage regresses but
its fibrous envelop
persists as
- the anterior ligament of
the malleus & spheno
mandibular ligament.
• Fibrous membrane of
ventral part of the
meckel’s cartilage is
ossified to form the body
of the mandible
Dr Ndayisaba Corneille

16. Second arch/hyoid arch:
• The cartilaginous part of this
arch is called Reichert’s
cartilage.
• Dorsal part of the cartilage is
ossified to form stapes of the
middle ear.
• Succeeding part of the
cartilage forms styloid
process of temporal bone
and stylohyoid ligament .
• Ventral part of the cartilage
is converted into lesser
cornu and upper part of body
of the hyoid bone.
Dr Ndayisaba Corneille

17. Third arch:
Dorsal part disappears ventral
part is ossified to form
greater cornu and lower part
of the body of hyoid bone.
Fourth arch:
Dorsal part disappears ventral
part forms the lamina of the
thyroid cartilage.
Sixth arch:
Dorsal part disappears ventral
part forms cricoid and
arytenoid cartilages.
Dr Ndayisaba Corneille

18. Dr Ndayisaba Corneille

19. Muscular derivatives
First arch:
Tensor tympani, tensor veli
palatini, muscles of
mastication, anterior belly of
digastric and mylohyoid
muscles.
Second arch:
Stapedius, stylohyoid,
muscles of the facial
expression, posterior belly
of digastric, platysma,
auricular muscles,
epicranius muscles.
Dr Ndayisaba Corneille

20. Third arch:
Stylopharyngeus muscle
Supplied by
glossopharyngeal nerve
Fourth arch:
Cricothyroid muscle by
external laryngeal nerve
which is a branch of
superior laryngeal nerve
Sixth arch:
All intrinsic muscle of the
larynx except cricothyroid
are supplied by the
recurrent laryngeal nerve.
Dr Ndayisaba Corneille

21. Dr Ndayisaba Corneille

22. Dr Ndayisaba Corneille

23. Dr Ndayisaba Corneille

24. Dr Ndayisaba Corneille

25. Summary of the fate of aortic arch arteries
• First arch:- Mostly disappears except partly for maxillary
artery.
• Second arch :- Mostly regresses except dorsal part for the
stapedial artery.
• Third arch :- Ventral part forms common carotid artery
dorsal part forms stem of internal carotid artery .
• Fourth arch:- Right side it forms proximal part of right
subclavian artery, left side it persists part of arch of aorta.
• Fifth arch :-Disappears entirely.
• Sixth arch :-
-On right side the ventral part persists as right pulmonary
artery dorsal part disappears .
-On the left side the ventral part forms the left
pulmonary artery and the dorsal part persist as ductus
arteriosus in fetal life /ligamentum arteriosum after birth.
Dr Ndayisaba Corneille

26. ANAMOLIES:
First arch syndrome:
• Results in various congenital anamolies of eyes, ears ,
mandible & palate.
• Due to insufficient migration of neural crest cells into
the first arch during the fourth week of development.
Dr Ndayisaba Corneille

27. 2. Treacher collins
syndrome:(Mandibulo-facial
dysostosis)
It is characterised by malar
hypoplasia (under
development of zygomatic
bone), mandibular
hypoplasia, down slanting
palpebral fissures, defects in
lower eyelid & mal formed
external ears.
3. Pierre Robin syndrome:
Hypoplasia of the mandible,
cleft palate & defect in the
eyes and ears. Dr Ndayisaba Corneille

28. Pharyngeal pouches:
• 5 pharyngeal pouches.
• 5th pouch is rudimentary.
• Ventral part of each pouch is obliterated by
developing tongue rudiments.
• Dorsal part (expect 1st pouch) divides into ventral &
dorsal wings.
Dr Ndayisaba Corneille

29. First pouch:
• Dorsal part extends into
adjacent mesenchyma
as Tubo tympanic
recess.
• Medial portion of this
recess is narrow and
persists. as “AUDITORY
TUBE”.
• Lateral part dilates to
form primitive tympanic
cavity
• Tympanic cavity gives
development to, mastoid
antrum , mastoid air cells
and mucous layer of
tympanic membrane.Dr Ndayisaba Corneille

30. • The blind distal end of the
tubo tympanic recess comes
in close contact with bottom
of the first brachial cleft
separated by a thin layer of
mesenchyme.
• This area forms into future
tympanic membrane which is
tridermal in development
involving the 3 primitive
germinal layers.
• The cuticular layer from
ectoderm, fibrous layer from
the mesoderm, and the
mucous layer from the tubo-
tympanic recess of
endoderm.
Dr Ndayisaba Corneille

31. Second pouch:
• Dorsal wing of the 2nd pouch
joins with first pouch and
contributes in the formation
of the tubotympanic recess.
• Endodermal cells of the
ventral wing of the 2nd pouch
proliferate into number of tiny
solid buds which extend into
adjoining mesenchyme.
• Central cells of these buds
undergoes destruction
leading into formation of
tonsillar pits and crypts.
• Lymphocytes are derived
from the circulating blood or
lymph stream.
Dr Ndayisaba Corneille

32. • Due to continuous
accumulation of the
lymphatic follicles
produces inward
bulging of the palatine
tonsil into the
pharynx.
• Thus most of the
ventral wing of the 2nd
pouch is obliterated
except a part which
persists as the
intratonsillar cleft.
Dr Ndayisaba Corneille

33. Third pouch:
• The dorsal wing of the 3rd
pouch is differentiated earlier
into inferior parathyroid.
• The ventral wing of the 3rd
pouch grows caudally as solid
thymic rudiment.
• Both the wings of pouch
communicate with the primitive
pharynx by superior
pharyngobranchial duct.
• The descent of heart and aortic
sac allows caudal migration of
the thymic rudiment dragging
the inferior parathyroid.
Dr Ndayisaba Corneille

34. • As a result inferior
parathyroid sweep along the
dorsal surface of the lateral
lobes of the thyroid gland.
• Finally they are
disconnected from thymus
and gain permanent
attachment to the lower pole
of the thyroid lobes.
• Lymphocytes in the thymic
rudiments are from stem
cells of the bone marrow.
Dr Ndayisaba Corneille

35. Fourth pouch:
• The dorsal wind of the fourth
pouch develops into
promodium of the superior
parathyroid.
• The ventral wing of the 4th
pouch joins with rudimentary
fifth pouch and forms the
caudal pharyngeal complex.
• Dorsal wing and complex
communicate with the
pharynx by the inferior
pharyngobrachial duct which
eventually rupture.
Dr Ndayisaba Corneille

36. This complex exhibits three
elements:
Thymic Element:
Incorporated in the
development of thymus.
Lateral Thyroid Element:
Thyroid element of 4th
pouch fuses with the
median thyroid rudiment.
Ultimobranchial body:
It plungs into the
substance of thyroid
rudiment and persists as
the parafollicular cells.
Dr Ndayisaba Corneille

37. First pouch Ventral part of the tongue
Tubotympanic recess
Second pouch Ventral part –tonsil
Dorsal part – tubotympanic recess
Third pouch Thymus
Inferior parathyroid
Fourth pouch Superior parathyroid
Thyroid gland
Fifth pouch Ultimobranchial body
Caudal pharyngeal complex
Dr Ndayisaba Corneille

38. Floor of the Primitive Pharynx(Ventral derivatives):
The floor o the primitive pharynx exhibits 3 features.
- Tongue
- Thyroid Gland
- Laryngo-tracheal groove
Dr Ndayisaba Corneille

39. THE TONGUE:
• The tongue appears in the
embryo of approximately
4 weeks in the form of
two lateral lingual
swelling, one medial
swelling the tubuerculum
impar originates from the
first pharyngeal arch.
• The 2nd median swelling
called the Hypobranchial
eminence is formed by
mesoderm of 2nd,3rd and
part of the 4th arch.
Dr Ndayisaba Corneille

40. Dr Ndayisaba Corneille

41. Mucous membrane
• Anterior 2/3rd – pair of
lingual swellings (endoderm
of the first arch) and median
tuberculum impar
• Posterior 1/3 rd –
Hypobranchial eminence
(fusion of 2nd, 3rd and 4th
arch)
• Posteriormost part – Fourth
arch
Muscles of the tongue –
Occipital myotomes
Connective tissue – Local
mesodem
Dr Ndayisaba Corneille

42. • Finally 3rd median swelling formed from the
posterior part of the 4th arch gives the
development of epiglottis.
• Immediately behind the swelling is the
laryngeal orifice, which is flanked by the
arytenoid swellings.
• The epiglottis and the extreme posterior part of
the tongue are innervated by the superior
laryngeal nerve, reflecting there development
from the 4th arch.
Dr Ndayisaba Corneille

43. Dr Ndayisaba Corneille

44. Developmental anamolies
of the tongue:-
Aglossia:- This is due to
complete agenesis of the
tongue rudiments.
Hemi-glossia:- This is
caused by the supression
of one of the lingual
swellings.
Bifid tongue:- The anterior
part of the tongue splits
into two, and is caused
by the failure of fusion of
the two lingual swellings.
Dr Ndayisaba Corneille

45. Dr Ndayisaba Corneille

46. Ankylo-glossia (or) tongue tie:
When alveolo-lingual sulcus separates the tongue
imperfectly, the movements of the tongue are
restricted so much that the lingual speech is
disturbed. It is manifested by the shortening of the
frenulum linguae.
Dr Ndayisaba Corneille

47. Development of the thyroid gland
• Endodermal diverticulum – thyroglossal duct
• Which grows caudally from the floor of the
primitive pharynx,behind the tuberculum impar
• The lower bifid end proliferates to give thyroid
gland
• Part of the lateral lobe develops from fourth
pharyngeal pouch
• Foetal functioning of thyroid begins between 18th
& 22nd week
Dr Ndayisaba Corneille

48. Dr Ndayisaba Corneille

49. Developmental anamolies of the thyroid:
1. Thyroglossal cyst (or) fistula:
2. Lingual thyroid: Arrested caudal growth of the
thyroglossal duct may lead to the development of the
thyroid gland within the tongue.
Dr Ndayisaba Corneille

50. Dr Ndayisaba Corneille

51. Accessory thyroid:- Sometimes nodules of thyroid
tissue are found in close proximity to the main gland.
Ectopic thyroid:- On rare occasions the thyroid grows
in the posterior triangle of the neck/in the thorax.
Agenesis of the thyroid:- Complete absence of the
thyroid gland is a rare phenomenon. It probably
occurs when the anti thyroid antibodies appear within
the mother, which might prevent the growth of the
foetal thyroid tissue after passing through the
placental barrier.
Dr Ndayisaba Corneille

52. Dr Ndayisaba Corneille

53. Dr Ndayisaba Corneille

54. END
Dr Ndayisaba Corneille
THANKS FOR LISTENING
By
DR NDAYISABA CORNEILLE
MBChB,DCM,BCSIT,CCNA
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