Embryology of the Head,

1
Embryology of the Head, Face and Oral Cavity
2
Prenatal Development
Figure from Ten Cates Oral Histology, Ed.,
Antonio Nanci, 6th edition
3
Differentiation of the Morula into Blastocyst
Figure from Ten Cates 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 Cates 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 differentiati
on of nervous tissue from ectoderm differentiati
on of neural crest cells (ectoderm) differentiat
ion of mesoderm folding of the embryo (2
planes-rostrocaudal and lateral)
8
Formation of neural tube and neural groove
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 Intermedi
ate 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 Cates 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 Cates Oral Histology, Ed.,
Antonio Nanci, 6th edition
12
Figure from Ten Cates 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 Cates Oral Histology, Ed.,
Antonio Nanci, 6th edition
15
Head Formation
(one of the first are the occipital somites)
Rhombomeres
Figure from Ten Cates Oral Histology, Ed.,
Antonio Nanci, 6th edition
16
Neural Crest Cell Migration
Figure from Ten Cates 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
Buccopharyngeal membrane ruptures at 24 to 26 days
Sagittal section through a 25-day embryo
Figure from Ten Cates 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 Cates Oral Histology, Ed.,
Antonio Nanci, 6th edition
23
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 Meckels
• Cartilage of 2nd arch Reicherts
• 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
Meckels 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 Reicherts 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
Table obtained from Before We Were Born Moore
and Persaud, 6th edition, 2003.
32
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.

33
Details of the aortic arch changes during early
development. Aortic arch vessels numbers 1,2 and
5 disappear . Arch 3 becomes the common carotid
artery. Arch 4 becomes the dorsal aorta and
enlarges so that the common carotid arises from
the aorta. Arch 6 becomes the right and left
pulmonary arteries
34
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

35
Muscle cells in the first arch become
apparent during the 5th week and begin to spread
within the mandibular arch into each muscle
sites 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
36
Masticatory muscles of the mandibular arch
Facial muscles grow from the 2nd branchial arch
to cover the face, scalp and posterior to the ear
37
Cranial Nerves growing into Branchial Arches
38
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
39
Anomalies of the head and neck

• Congenital auricular sinuses and cysts
• Branchial cysts
• Branchial sinuses
• Branchial fistula
• Branchial vestiges
• (cartilaginous or bony remnants)
• Branchial cysts

Dermatlas
Dermatlas
40
Apparent fusion of facial processes
by elimination of furrows
True fusion of facial processes by breakdown of
surface epithelium
Figure from Ten Cates Oral Histology, Ed.,
Antonio Nanci, 6th edition
41
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.
42
Frontonasal process
Figures obtained from Before We Were Born Moore
and Persaud, 6th edition, 2003.
43
Figures obtained from Before We Were Born Moore
and Persaud, 6th edition, 2003.
44
Figures obtained from Before We Were Born Moore
and Persaud, 6th edition, 2003.
45
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
46
Human embryo at 7 weeks
Figure from Ten Cates Oral Histology, Ed.,
Antonio Nanci, 6th edition
47
Cleft Lip
48
Pituitary Gland Development

• Ectodermal in origin and develops from 2 sources
• An upgrowth from the ectodermal roof of the
  stomatodeum
• called hypophysial diverticulum (Rathkes Pouch)
  - adenohypophysis
• A downgrowth from the neuroectoderm of the
  diencephalon
• called the neurohypophysial diverticulum
  neurohypophysis
• During the 4th week of development, a hypophysial
  diverticulum
• (Rathkes 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)

49
Figures obtained from Before We Were Born Moore
and Persaud, 6th edition, 2003.
50
Figures obtained from Before We Were Born Moore
and Persaud, 6th edition, 2003.
51
Derivation and Terminology of the Pituitary Gland
Oral Ectoderm Adenohypophysis Pars
distalis (hypophysial diverticulum
(glandular portion) Pars tuberalis from roof of
stomodeum) Pars intermedia Neuroectoderm Neur
ohypophysis Pars nervosa (neurohypophysial
(nervous portion) Infundibular stem diverticulum
from Median eminence floor of diencephalon)
Clinical Significance Craniopharyngiomas
develop from remnants of stalk of hypophysial
diverticulum (in pharynx of sphenoid bone)
52
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
53
Formation of the secondary palate (starts between
7 to 8 weeks and completed around 3 months)
Figure from Ten Cates Oral Histology, Ed.,
Antonio Nanci, 6th edition
54
Figure from Ten Cates Oral Histology, Ed.,
Antonio Nanci, 6th edition
55
Cleft Palate
56
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 2nd, 3rd and 4th
branchial arches. Innervation IX cranial
nerveThe 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
57
Lingual swelling
Tuberculum impar
Figures obtained from Before We Were Born Moore
and Persaud, 6th edition, 2003.
58
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59
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
60
Thyroid gland development (4 to 7 weeks)
Figures obtained from Before We Were Born Moore
and Persaud, 6th edition, 2003.
61
Lingual thyroid
Thyroglossal duct cyst
62
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63
Development of Jaw Bones
Figure from Ten Cates Oral Histology, Ed.,
Antonio Nanci, 6th edition
64
Development of Mandible
Figure from Ten Cates Oral Histology, Ed.,
Antonio Nanci, 6th edition
65
Figure from Ten Cates Oral Histology, Ed.,
Antonio Nanci, 6th edition
66
Figure from Ten Cates Oral Histology, Ed.,
Antonio Nanci, 6th edition
67
Fate of Meckels Cartilage
Posterior malleus of the inner
ear Sphenomandibular ligament Anteriorly, may
contribute to mandible by endochondral
ossification (some evidence) Rest are resorbed
completely
68
Secondary Cartilages

• Three secondary (growth) cartilages govern
  further growth of
• mandible until birth
• Condylar cartilage (most important)
• Coronoid cartilage
• Symphysial cartilage

69
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 Cates Oral Histology, Ed.,
Antonio Nanci, 6th edition
70
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
71
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