1. Embryology of the Head,
Face and Oral Cavity

2. Prenatal Development
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

3. Differentiation of the Morula into Blastocyst
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

4. Formation of Two-Layered Embryo (2nd week of gestation)
Called bilaminar germ disk
Ectoderm
Endoderm
Pre/prochordal plate
Firm union between ectodermal and
endodermal cells occur at prechordal
plate
Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.

5. Formation of Three-Layered Embryo: Gastrulation (3rd week)
Triploblastic embryo
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

6. Formation of Three-Layered Embryo: Gastrulation (3rd week)
Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.

7. First 3 weeks: Leads to formation of triploblastic embryo
Next 3-4 weeks: differentiation of major tissues and organs
includes head and face and tissues responsible
for teeth development
differentiation of nervous tissue from ectoderm
differentiation of neural crest cells (ectoderm)
differentiation of mesoderm
folding of the embryo (2 planes-rostrocaudal and lateral)

8. Formation of neural tube and neural groove
Neural tube undergoes massive expansion to form the forebrain,
midbrain and hindbrain
Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.

9. Components of the mesoderm
Along the trunk paraxial mesoderm breaks up into segmented
blocks called somites
Each somite has: sclerotome- 2 adjacent vertebrae and disks
myotome-muscle
dermatome-connective tissue of the skin over the somite
In the head region the paraxial mesoderm only partially fragments to form a series
of numbered somatomeres which contribute to head and neck musculature
Intermediate mesoderm: urogenital system
Lateral plate mesoderm: connective tissue of muscle annd viscera; serous
membranes of the pleura; pericardium and peritoneum; blood and lymphatic cells;
cardiovascular and lympahtic systems, spleen and adrenal cortex.
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

10. In the head, the neural tube undergoes massive expansion to form
the forebrain, midbrain and hindbrain
The hindbrain segments into series of eight bulges called
rhombomeres which play an important role in development of the head

11. Folding of the Embryo Head fold forms a primitive
stomatodeum or oral cavity; leading
to ectoderm lining the stomatodeum
and the stomatodeum separated from
the gut by buccopharyngeal membrane
Onset of folding is at 24 days and
continues till the end of week 4
Embryo just before folding (21 days)
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

12. Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

13. Neural Crest Cells
Group of cells separate from the neuroectoderm, migrate and
differentiate extensively leading to formation of cranial sensory
ganglia and most of the connective tissue of the head
Embryonic connective tissue elsewhere is derived form mesoderm
and is known as mesenchyme
But in the head it is known as ectomesenchyme because of its
origin from neuroectoderm
Look up Fig 2-12 in text book for derivative of the germ layers
and neural crest

14. Avian neural crest cells
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

15. Head Formation (one of the first are the occipital somites)
Rhombomeres
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

16. Neural Crest Cell Migration
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

17. Pharyngeal arches expand by proliferation of
neural crest cells
Forebrain
(prosencephalon)
Midbrain
(mesencephalon) r3
Hindbrain
(rhombencephalon) r5
Couly et al., 2002

18. Migration of cranial neural crest cells
Anterior midbrain
FNM E TG
Posterior midbrain E TG Md
Anterior hindbrain E TG Md
Imai et al., 1996

19. Clinical Correlation
Treacher Collins Syndrome is characterized by defects of
structures that are derived form the 1st and 2nd branchial arches and
is due to failure of neural crest cells to migrate properly to the
facial region

20. Sagittal section through a 25-day embryo
Buccopharyngeal membrane ruptures at 24 to 26 days
Sagittal section through a 25-day embryo
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

21. Internal View of the Oral Pit at 3.5 weeks

22. 26-day embryo
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

23. The pharyngeal apparatus
groove/cleft
pouch
arch
membrane
esophagus
The pharyngeal apparatus 1 2 3 4
Branchial arches form in the pharyngeal wall (which has lateral plate mesoderm sandwiched
between ectoderm and endoderm) as a result of lateral plate mesoderm proliferation and
subsequent migration by neural crest cells
The Developing Human by Moore & Persaud

24. 3 weeks

25. Sagittal view of the branchial arches with corresponding grooves between each arch.
Pharyngeal pouches are seen in the wall of the pharynx. The aortic arch vasculature
leads from the heart dorsally through the arches to the face

26. Fate of the Pharyngeal Grooves and Pouches
First groove and pouch: external auditory meatus
tympanic membrane
tympanic antrum
mastoid antrum
pharyngotympanic or eustachian tube
2nd, 3rd and 4th grooves are obliterated by overgrowth of the second
arch forming a cervical sinus – if persists forms the branchial fistula
that opens into the side of the neck extending form the tonsillar sinus
2nd pouch is obliterated by development of palatine tonsil
3rd pouch: dorsally forms inferior parathyroid gland
ventrally forms the thymus gland by fusing with the
counterpart from opposite side

27. 4th pouch: dorsal gives rise to the superior parathyroid gland
ventral gives rise to the ultimobranchial body (which
gives rise to the parafollicular cells of the thyroid gland)
5th pouch in humans is incorporated with the 4th pouch

28. (A) Tissue from arch II and V growing towards each other (arrows) to make branchial
arches and grooves disappear
(B) Resulting appearance following overgrowth
(C) Contribution of each pharyngeal pouch

29. Anatomy of the Branchial Arches
Cartilage of 1st arch: Meckel’s
Cartilage of 2nd arch: Reichert’s
Other arches not named
Some mesenchyme around cartilage
gives rise to striated muscle
Each arch also has an artery and nerve
Nerve: two components (motor and
sensory)
Sensory nerve divides into 2 branches:
Posttrematic branch: covers the anterior
half of the arch epithelium
Prettrematic: covers the posterior half
of the arch epithelium
Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.

30. Meckel’s cartilage: Has a close relationship with the
developing mandible BUT DOES NOT CONTRIBUTE TO IT
Indicates the position of the future mandible. The mandible develops by intramembranous ossification. The malleus and the incus develop by endochondral ossification of
the dorsal aspect of this cartilage. Innervation: V cranial nerve
Reichert’s: Dorsal end: stapes and styloid process
Ventral end: lesser horns of hyoid bone and superior
part of the body of the hyoid bone
Innervation: VII cranial nerve
Cartilage of the 3rd arch: inferior part of the body and greater
horns of the hyoid bone
Cartilage of 4th and 6th arches: fuse to form the laryngeal cartilage

31. Aortic Vasculature Development
At 4 weeks the anterior vessels have passed through each branchial arch tissue
and have disappeared. The pouches project laterally between each arch.
At 5 weeks the 3rd branchial arch vessel becomes the common carotid, which
supplies the face by means of the internal carotid and stapedial arteries.
Face, Neck and Brain are supplied by the common carotid through internal carotid.
But by 7 weeks the circulation of face and neck shifts from the internal carotid to
external carotid. The internal carotid continues to supply the brain.

32. Shift in the vascular supply to the face
Face and brain are supplied first by the internal carotid artery
Facial vessels detach from the internal carotid and attach to the
external carotid

33. Muscle cells in the first arch become apparent
during the 5th week and begin to spread within
the mandibular arch into each muscle site’s
origin in the 6th and 7th week. These form the
muscles of mastication – masseter, medial
pterygoid, lateral pterygoid and temporalis
muscle. They all relate to the developing mandible
By 7 weeks the muscles of 2nd arch grow
upward to form the muscles of face.
As these muscles grow and expand they
forms sheet over the face and forms the
muscles of facial expression

34. Masticatory muscles of the mandibular arch
Facial muscles grow from
the 2nd branchial arch to cover
the face, scalp and posterior
to the ear

35. Cranial Nerves growing into Branchial Arches

36. Cartilages derived from the
branchial arches
Arch 1: Meckels cartilage and incus
Arch 2: Stapes, stylohyoid and lesser
hyoid
Arch 3: Greater hyoid
Arch 4 and 6 thyroid and
laryngeal cartilage

37. Anomalies of the head and neck
Congenital auricular sinuses and cysts
Branchial cysts
Branchial sinuses
Branchial fistula
Branchial vestiges
(cartilaginous or bony remnants)
Dermatlas
Dermatlas

38. Apparent fusion of facial processes by elimination of furrows
True fusion of facial processes by
breakdown of surface epithelium
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

39. Development of the Face
The face develops between the 24th and 38th days of gestation
On 24th day, the 1st branchial arch divides into maxillary and mandibular arches
Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.

40. Frontonasal process
Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.

41. Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.

42. Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.

43. Formation of the Lips
Middle portion of the upper lip: Formed by the fusion of the medial
nasal process of both sides along with the frontonasal process
Lateral portion of the upper lip: Fusion of the maxillary processes
of each side and medial nasal process
Lower lip: Formed by the fusion of the two mandibular processes
Unusual fusion between maxillary process and lateral nasal process
leading to canalization and formation of the nasolacrimal duct

44. Human embryo at 7 weeks
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

45. Cleft Lip
are variations of a type of clefting congenital deformity caused by abnormal facial development during gestation
Genetic factors contributing to cleft lip and cleft palate formation have been identified for some syndromic cases, but knowledge about genetic factors that contribute to the more common isolated cases of cleft lip/palate is still patchy.

46. Pituitary Gland Development
Ectodermal in origin and develops from 2 sources:
An upgrowth from the ectodermal roof of the stomatodeum
called hypophysial diverticulum (Rathke’s Pouch) - adenohypophysis
A downgrowth from the neuroectoderm of the diencephalon
called the neurohypophysial diverticulum – neurohypophysis
During the 4th week of development, a hypophysial diverticulum
(Rathke’s pouch) projects from the roof of the stomatodeum and lies
adjacent to the floor (ventral wall) of the diencephalon. By the 5th
week, this pouch has elongated and has become constricted
at its attachment to the oral epithelium and is in contact with the
infundibulum (derived from the neurohypophysis)

47. Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.

48. Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.

49. Derivation and Terminology of the Pituitary Gland
Oral Ectoderm Adenohypophysis Pars distalis (distal part)
(hypophysial diverticulum (glandular portion) Pars tuberalis (tubular part)
from roof of stomodeum) Pars intermedia
(intermediate part)
Neuroectoderm Neurohypophysis Pars nervosa
(neurohypophysial (nervous portion) (posterior pituitory)
diverticulum from
floor of diencephalon)

50. Formation of the palate (weeks 7 to 9)
Palate develops from the primary palate and the secondary palate
The primary palate develops at about 28 days of gestation
Primary palate develops from the frontonasal and medial nasal
processes and eventually forms the premaxillary portion of the maxilla
The secondary palate develops between 7th and 8th week of gestation
and completes in the 3rd month
The critical period of palate development is from the end of 6th week
till the beginning of 9th week

51. Formation of the secondary palate
(starts between 7 to 8 weeks and completed around 3 months)
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

52. Formation of the Tongue
The tongue begins to develop at about 4 weeks. The oral part (anterior two-thirds) develops from two distal tongue buds (lateral lingual swellings) and a median tongue bud (tuberculum impar) [1st branchial arch]. Innervation: V nerve The pharyngeal part develops from the copula and the hypobranchial eminence (hill) [2nd, 3rd and 4th branchial arches]. Innervation: IX cranial nerve The line of fusion of the oral and pharyngeal parts of the tongue is roughly indicated in the adult by a V-shaped line called the terminal sulcus. At the apex of the terminal sulcus is the foramen cecum.
Muscles of the tongue develop form the occipital somites and innervated by hypoglossal nerve

53. Lingual swelling
Tuberculum impar
Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.

55. The lingual papillae appear by the end of 8th week
Vallate and foliate papillae appear first, fungiform and
filiform (10-11 weeks) papillae appear later
Taste buds develop during the 11 to 13 weeks by inductive
interaction between epithelial cells of the tongue and invading
gustatory nerve cells from chorda tympani, glossopharyngeal
and vagus nerves

56. Thyroid gland development (4 to 7 weeks)
Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.

57. Lingual thyroid results from lack of normal caudal migration of the thyroid gland.
Thyroglossal duct cystis a neck mass or lump that develops from cells and tissues remaining after the formation of the thyroid gland during embryonic development

59. Development of Jaw Bones
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

60. Development of Mandible
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

61. Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

62. Fate of Meckel’s Cartilage
Posterior – malleus of the inner ear
Sphenomandibular ligament
Anteriorly, may contribute to mandible
by endochondral ossification (some evidence)
Rest are resorbed completely

63. Secondary Cartilages
Three secondary (growth) cartilages govern further growth of
mandible until birth
Condylar cartilage (most important)
Coronoid cartilage
Symphysial cartilage

64. Appears during 12th week and occupies most
of the ramus and is quickly ossified by
endochondral ossification, with a very thin
layer of cartilage present in the condylar head.
This remnant persists until 2nd decade of life
and is important for growth of mandible
Appears at 4 months and
disappears immediately
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

65. Development of Maxilla
Develops from one center of ossification in maxillary process of
the 1st branchial arch
Center of ossification is angle between the divisions where the
anterosuperior dental nerve is given off from inferior orbital nerve
from where it spreads posteriorly, anteriorly and superiorly
No arch cartilage is present, so maxilla develops in close
association with the nasal cartilage
One secondary cartilage also contributes to maxilla
development: zygomatic cartilage

66. GROWTH OF THE MANDIBLE MORE DETAILS Condyle Lingula
NOTE THE DIVERGANCE OF THE RAMI STARTING FROM THE SITE OF THE LINGULAE

67. SUMMARY OF GROWTH I – CONDYLAR GROWTH
A – Increase Ramus’s Height
B – Increase Mandibule’s Length.
C – Increase Inter-condylar Distance.
II - BONE APPOSITION AND BONE RESORPTION:
A – Increase The Body Length.
B – Increase The Body Height.
C – Increase The Body Strength.
D – Increase The Distance Between The Mandibular Canal And The Teeth
Roots.
E – Adjust The Ramus’s Width..
F - Widening Of The Mandible And Increase Its Transverse Dimension.

68. Thyroglossal cyst and Fistula: Cysts and fistulae found along the midline of the neck usually develop from remnants of thyroglossal duct.
Generally, thyroglossal cysts maybe found at any point along the course of the thyroglossal duct but it is usually found at the level of the hyoid bone and the thyroid cartilage.
Mandibulofacial Dysostosis or Treacher Collins Syndrome: This results from failure or incomplete migration of the neural crest cells to the facial region.
The zygomatic bone is severely hypoplastic . The face appears to be drooping, and the ears are usually malformed. The lower border of the mandible appears concave, and cleft palate is occasionally seen.

69. Abnormal Development
Fissural cysts: Cystic cavities which arise along the fusion of various bones or embryonic processes and lined by epithelium.
Median Rhomboid Glossitis: It results from persistence of the tuberculum impar and characterised by a red smooth region anterior to the foramen caecum.
Ankyloglossia: This occurs as a result of incomplete degeneration of cells while the body of the tongue is freed, so that the tip of the tongue remains tied to the floor of the mouth.
Macroglossia: or abnormally large tongue is not common, but is seen sometimes at birth when tongue slightly protrudes from mouth. This corrects itself when the jaws grow at a rapid rate. True macroglossia is seen in mongolism.
Bifid tongue: This is a malformation common in south American infants and is the result of failure of the lateral lingual swellings.

70. Developmental Anomalies
Hare lip
Oblique facial cleft
Cleft palate
Macrostomia
Microstomia
Hypertelorism
Congenital lip pits or fistulae
Double lip
Congenital tumours in relation to the face
Bifid nose