2. INTRODUCTION
 After folding, the secondry yolk sac inside
the embryo gives rise to:Fore gut-Mid gut–hind gut.
The fore gut is divided into :
a. Cranial part : extends from oral
membrane to the laryngo-tracheal groove.
It gives rise to :
 Part of mouth cavity
 Salivary glands
 Pharyngeal apparatus
 Respiratory system
b. Caudal part : begins distal to the laryngotracheal groove.
It gives rise to: esophagus-stomach- part of duodenum-
liver-biliary system –pancreas.
Amniotic
cavity
Oral
membrane
Gut
Cloacal
membrane
Yolk sac
Before folding
Stomodeum
Vitello-intestinal
duct
Allantois Cloacal
membrane
Hindgut
Midgut
Foregut
Connecting stalk
Amniotic cavity
After folding

3. THE PHARYNGEAL ARCHES
They are 6 curved cylindrical mesenchymal
thickening on each side of the primitive pharynx.
They develop in the head & neck similar in origin &
structure to gills of the fish.
Gill = Branchia
 Each arch consists of :
1. Outer ectodermal covering
2. Inner endodermal lining
3. Mesodermal core

4.  Each pharyngeal arch consists, at first of
mesenchyme derived from the lateral plate
mesoderm.
 Soon, neural crest cells migrate into the
pharyngeal arches and surround the central
core of mesenchymal cells.
 Migration of neural crest cells into the arches
produce discrete swelling demarcating each of
the pharyngeal arch.
 NB. Mesenchyme =connective tissue of embryo
 The mesenchyme derived from neural crest
cells is called (ectomesenchyme) to
differentiate it from mesenchyme derived
from mesoderm.

5. A typical pharyngeal arch
contains:
1- A cartilaginous rod that forms
the skeleton of the arch.
2- A muscular component that
differentiates into muscles in the
head and neck.
3- An aortic arch , an artery that
arises from the truncus arteriosus
of the primordial heart.
4- A nerve that supplies the
mucosa and muscles derived from
the arch.

6. NERVE SUPPLY OF THE PHARYNGEAL ARCHES
 It is derived from the
hindbrain (pons and
Medola oblogata)
 Each arch receives
mixed nerve.
 Its motor branch
supplies muscles derived
from the arch.
 Its sensory branch
supplies skin and
mucous membrane of
the arch.

7. DEVELOPMENT OF PHARYNGEAL ARCHES
•By the end of the 4th week, 4 well defined pairs of pharyngeal arches
are visible externally.
•The 5th and 6th arches are small and cannot be seen on the surface of
the embryo.

8.  Most of the cartilages that form within the
pharyngeal arches develop from the neural crest of
the midbrain and hindbrain regions, although the
cartilages of arches 4 and 6 apparently develop from
lateral plate mesoderm.
 The first pharyngeal arch is remodeled to form a
cranial maxillary process and a caudal mandibular
process.
 Each process contains a central cartilaginous element
(the maxillary is known as palato-pterygo-quadrate
cartilage and the mandibular is known as Meckel's
cartilage) surrounded by a mesenchymatic tissue.
Cartilages

9. PHARYNGEAL ARCHES CONTI..

10. P R O F . M O H A M E D . A . A U T I F I
Arch Skeletal
Derivatives
Muscular
Derivatives
Vascular
Element
Nerve
First arch
(mandibular
arch)
Consists of
maxillary
process
and
mandibular
process
Maxillary process
gives rise to:
1. Maxilla
2. Zygomatic
bone
3. Squamous part
of temporal
bone
Mandibular
process
differentiates into :
1. Malleus
2. Incus
3. Anterior
ligament of
malleus
4. Spheno-
mandibular
ligament
5. Mandible
1.Muscles of
Mastication
2.Tensor
palati
3.Tensor
tympani
4. Mylohoid
5. Anterior
belly of
digastric
1. Maxillary
artery
Mandibular
nerve (V)

11. Derivatives of Cartilages of First Pharyngeal Arch
The ventral part of the
first arch cartilage (
Meckel cartilage ) form
primordium of the
mandible
The middle part of
cartilage forms anterior
ligament of malleus and
sphenomandibular
ligament
The dorsal end of first
arch cartilage
ossifies to form
malleus and incus
More details about cartilages

12. P R O F . M O H A M E D . A . A U T I F I
Arch Skeletal
Derivatives
Muscular
Derivatives
Vascular
Element
Nerve
Second arch
(Hyoid arch)
Reichert’s
cartilage:
Differentiates
into:
1. Stapes
2. Styloid
process
3. Stylohyoid
ligament
4. LeSser horn
of the hyoid
bone
5. Superior(Uppe
r)part of body
of hyoid bone
1. Muscles of
the scalp
and face
2. Platysma
3. Stylohyoid
4. Stapedius
5. Posterior
belly of
digastric
Stapedial
Artery
tympanic br.
of ICA)
Facial nerve
(VII)

13. Derivatives of Cartilage of second Pharyngeal Arch
The ventral end of second arch
cartilage (Reichert cartilage)
ossifies to form the lesser cornu
and upper part of the body of
the hyoid bone
The dorsal end of second arch
cartilage (Reichert cartilage)
ossifies to form the stapes,
styloid process and stylohyoid
ligament

14. Arch Skeletal
derivatives
Muscular
derivatives
Vascular
Element
Nerve
Third arch 1. Greater horn of
hyoid bone
2. Lower part of
body of hyoid bone
Stylopharyngeus 1. I.C.A
2. C.C.A
Glossopharyngeal
nerve (IX)
Fourth arch Thyroid cartilage Cricothyroid 1. Arch of aorta
on left side
2. Subclavian A
on right side
Superior laryngeal
nerve (X)
Sixth arch Rest of Cartilages
of the larynx except
epiglottis:
-Cricoid,
-Arytenoid,
-Corniculate
and
-Cuneiform.
NB. The epiglottis
develops from
mesenchyme in
hypobrancheal
eminence
1. Other intrensic
muscles of larynx
2. Constrector
muscles of pharynx
except
Stylopharyngeus
3. Muscles of
palate except
tensor palati
1. Pulmonary A
on each sides
2. Ductus
arteriosus
on left side
Recurrent laryngeal
nerve (X)

15. Derivatives of Third Pharyngeal Arch Cartilage
The third arch cartilage ossifies to
form the greater cornu and the
lower part of the body of the hyoid
bone

16. • The fourth and sixth arch
cartilages fuse to form the
laryngeal cartilages except
epiglottis which develops
from hypobrancheal
eminence
• The fifth pharyngeal arch
is rudimentary and
disappear later and has no
derivatives
Derivatives of The fourth and sixth Pharyngeal Arch
Cartilages

17. Muscular component

18. PHARYNGEAL
POUCHES AND CLEFTS

19. DEVELOPMENT OF PHARYNGEAL POUCHES AND CLEFTS

20. PHARYNGEAL POUCHES
 The pharyngeal pouches are balloon-like diverticula that
formed on the endodermal side between the pharyngeal
arches
 The pairs of pouches develop in a craniocaudal sequence
between the arches.
 The first pair of pouches lies between the first and second
pharyngeal arches.
 There are four well defined pairs of pharyngeal pouches
 The fifth pair is absent or rudimentary
•

21. It gives rise to
tubotympanic recess
which forms:
1.Tympanic cavity
2.Auditory tube.
(pharyngotympanic
tube or Eustachian
tube)
First pouch

22. • Gives rise to palatine tonsils
• -Early in 3rd month, its lining
epithelium proliferates ➪
solid tonsillar buds which
grow into underlying
mesoderm.
• -Their central cells
degenerate➪ hollow tonsillar
crypts.
• -Crypts & surrounding
mesoderm ➪ palatine tonsils.
• -Lymphatic tissue infiltrates
its mesoderm during 3-5
Month
• -Tonsillar capsule formed by
condensed mesoderm.
• -Remnants of pouch ➪
intratonsillar cleft
Second pouch

23. Gives rise to:
-inferior parathyroid glands.
-thymus gland.
At 6th week, they lose connection to
pharyngeal wall.
-Thymus gland migrates caudally &
medially, pulling the parathyroid. The two
thymic rudiments descend into
thorax. Gland is large at time of birth, ➚
up to 2nd year, little ➚ until 7th year,
rapid growth to 11th year,
then ➘ to adult weight (12-15 gm)
-Inferior parathyroid glands descends
to lower pole of thyroid gland
Third pouch

24. It gives rise to:
1.Superior parathyroid glands.
It migrates with the thyroid gland.
2. Ultimo-branchial
body.
It incorporates into the thyroid
gland.
It gives parafollicular or C cells of
thyroid gland
Fourth pouch

25. PHARYNGEAL GROOVES
(CLEFTS):
In the 5th week: 4 clefts seen.
The first cleft gives:
external auditory meatus.
The epithelium of the bottom
forms outer layer of eardrum
NB. Active growth of 2nd arch
mesoderm overlaps 3rd & 4th
arches.
Temporarily, clefts ➪ectodermal
cavity, cervical sinus, which
disappears later.

26. DEVELOPMENT OF PHARYNGEAL POUCHES AND CLEFTS

29. 1. Branchial Cyst: Sinus persists as cyst along ant border
of sternomastoid muscle.
If ruptures ➪ branchial sinus
2. Branchial Sinus:
a) External: Cyst opens outside, usually anterior to
sternomastoid.
b) Internal: Cyst opens
into pharynx,usually
in the tonsillar region.
3. Cervical Fistula:
Sinus opens externally
& internally, connects
pharynx with outside.
Congenital anomalies

30. 4. 1st Arch Syndrome (Mandibulofacial dystosis)
Maldevelopment of components of 1st pharyngeal arch results
in various congenital malformations of eyes, ears, mandible
and palate. This is due to failures of Proper neural crest
migration into the 1st branchial arches.
5. DiGeorge Syndrome. Improper migration of neural crest
cells into the 3rd and 4th branchial arches.
It is characterized by:
1.Minor deformations of the lower face.
2.Thymic and parathyroid aplasia (i.e., no thymus and no
parathyroids). The absence of a thymus has a very deleterious effect on the
development of the immune system. The absence of parathyroids leads to
hypocalcemia.
3.Problems with aorticopulmonary septation.
Congenital anomalies

31. 6. Ectopic Thymic Tissue:
Thymus gland lies in the neck.
7. Ectopic Parathyroid:
Inferior parathyroid may present at bifurcation of
Common carotid artery.
Congenital anomalies