The document summarizes the embryology of the head and neck region. It discusses that the mesenchyme that forms the head is derived from mesoderm, neural crest cells, and thickened ectoderm. There are 5 pairs of branchial arches that form the basis of all head and neck structures. Each arch contains mesenchyme, ectoderm, endoderm, blood vessels, cartilage, muscles and nerves. The arches give rise to many structures in the head and face through the ossification and differentiation of these components.

1. Embryology of Head and neck
• The mesenchyme for formation of the head region is derived from
mesoderm, neural crest, and thickened regions of ectoderm known as
ectodermal placodes.
G.LUFUKUJA

2. PHARYNGEAL APPARATUS
(Branchial arch)
• Neural crest cells originate in the neuroectoderm of
forebrain, midbrain, and hindbrain regions and migrate
ventrally into the pharyngeal arches and rostrally around the
forebrain and optic cup into the facial region. In these
locations they form mid-facial and pharyngeal arch skeletal
structures
• There are 5 pairs of branchial arches, that form on either side
of the pharyngeal foregut on day 22 are the embryologic
basis of all the differentiated structures of the head and neck

3. 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

4. Pharyngeal Apparatus
Pharyngeal apparatus consists of:
• Pharyngeal arches
• Pharyngeal pouches
• Pharyngeal grooves/clefts
• Pharyngeal membrane

5. Pharyngeal Arches
• Pharyngeal arches begin to develop early in the
fourth week as neural crest cells migrate into the
head and neck region
• The first pair of pharyngeal arches (primordium of
jaws) appears as a surface elevations lateral to the
developing pharynx
• Soon other arches appear as obliquely disposed,
rounded ridges on each side of the future head and
neck regions

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Branchial arches

9. 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

10. Pharyngeal Arches
• The first pharyngeal arch (mandibular arch)
develops maxillary and mandibular
prominences
• The first pair of pharyngeal arches plays a
major role in facial development
• The second pharyngeal arch (hyoid arch)
contributes to the formation of hyoid bone

12. 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

13. Fate of Pharyngeal Arches
• The pharyngeal arches contribute exclusively to the
formation of 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

15. 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

17. Derivatives of Pharyngeal Arch Cartilages
• The dorsal end of first arch cartilage (Meckel
cartilage) ossifies to form malleus and incus
• The middle part of cartilage forms anterior ligament
of malleus sphenomandibular ligament
• Ventral part of the first arch cartilages form
primordium of the mandible
• The cartilage disappears as mandible develops
around it

19. Derivatives of Pharyngeal Arch Cartilages
• The dorsal end of second arch cartilage (Reichert
cartilage) ossifies to form the stapes and styloid
process of the temporal bone
• The ventral end of second arch cartilage ossifies to
form the lesser cornu and superior part of the body
of the hyoid bone
• Its perichondrium forms the stylohyoid ligament

20. Derivatives of Pharyngeal Arch Cartilages
• The third arch cartilage ossifies to form the greater
cornu and the inferior part of the body of the hyoid
bone
• The fourth and sixth arch cartilages fuse to form the
laryngeal cartilages except epiglottis which develops
from hypopharyngeal eminence
• The fifth pharyngeal arch is rudimentary and has no
derivatives

22. Derivatives of Pharyngeal Arch Muscles
• The musculature of the first pharyngeal arch forms the
muscles of mastication
• The second pharyngeal arch forms the stapedius, stylohyoid,
posterior belly of digastric, auricular and muscles of facial
expression
• The third arch forms the stylopharyngeus
• The fourth arch forms cricothyroid, levator veli palatini and
constrictors of pharynx
• Sixth pharyngeal arch forms the intrinsic muscles of the larynx

24. Derivatives of Pharyngeal Arch Nerves
• Caudal two branches of Trigeminal nerve (maxillary and
mandibular) supply derivatives of the first pharyngeal arch
• The facial, glossopharyngeal and vagus nerves supply the
second, third and caudal (fourth to sixth) arches respectively
• The fourth arch is supplied by superior laryngeal branch of
vagus nerve
• The sixth arch is supplied by its recurrent laryngeal branch

26. Pharyngeal Pouches
• The primordial pharynx, derived from the foregut,
widens cranially where it joins the primordial mouth
or stomodeum
• It narrows caudally where it joins the esophagus
• The endoderm of the pharynx lines the internal
aspects of pharyngeal arches and passes into
balloonlike diverticula called pharyngeal pouches

28. Pharyngeal Pouches
• 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

29. Pharyngeal Pouches
• The endoderm of the pouches contacts the
ectoderm of the pharyngeal grooves and
together they form the double layered
pharyngeal membranes that separate the
pharyngeal pouches from the pharyngeal
grooves

30. Derivatives of First Pharyngeal Pouch
• The first pharyngeal pouch expands into an elongate
tubotympanic recess
• The expanded distal part of this recess contacts the
first pharyngeal groove, where it contributes to the
formation of the tympanic membrane (eardrum)
• The cavity of the tubotympanic recess gives rise to
the tympanic cavity and mastoid antrum

32. Derivatives of Second Pharyngeal Pouch
• The second pharyngeal pouch is largely obliterated
as the palatine tonsils develop
• Part of the cavity of this pouch remains as the
tonsillar sinus or fossa
• The endoderm of the pouch proliferates and grows
into the underlying mesenchyme
• The central parts of these buds form crypts

34. Derivatives of Second Pharyngeal Pouch
• The pouch endoderm forms the surface
epithelium and the lining of the tonsillar
crypts
• At about 20 weeks the mesenchyme around
the crypts differentiates into lymphoid tissue
• These tissues soon organize into the lymphatic
nodules of the palatine tonsil

35. Derivatives of Third Pharyngeal Pouch
• The third pharyngeal pouch expands and develops a
solid, dorsal bulbar part and a hollow elongate
ventral part
• Its connection with the pharynx is reduced to a
narrow duct that soon degenerates
• By the sixth week the epithelium of each dorsal
bulbar part begins to differentiate into inferior
parathyroid gland

36. Derivatives of Third Pharyngeal Pouch
• The epithelium of the elongate ventral parts of third
pharyngeal pouch proliferates and their cavities obliterate
• These bilateral primordia of thymus come together in the
median plane to form thymus
• It descends into the superior mediastenum
• The bilobed form of thymus remains throughout life
• Discretely encapsulated and each lobe has its own blood
supply, lymphatic drainage and nerve supply

38. Derivatives of Third Pharyngeal Pouch
• The primordia of thymus and parathyroid
glands lose their connections with the
pharynx and migrate into the neck
• Later the parathyroid glands separate from
the thymus and lie on the dorsal surface of the
thyroid gland

39. Derivatives of Fourth Pharyngeal Pouch
• The fourth pharyngeal pouch also expands into
dorsal bulbar and elongate ventral parts
• Its connection with the pharynx is reduced to a
narrow duct that soon degenerates
• By the sixth week, each dorsal part develops into a
superior parathyroid gland
• It lies on the dorsal surface of the thyroid gland

41. Derivatives of Fourth Pharyngeal Pouch
• The parathyroid glands derived from the third
pouches descend with the thymus and are
carried to a more inferior position than the
parathyroid derived from the fourth pouches
• This explains why the parathyroid glands
derived from the third pair of pouches are
located inferior to those from the fourth
pouches

42. The Fifth Pharyngeal Pouch
• When this develops, this rudimentary pouch
becomes part of the fourth pharyngeal pouch
and helps to form the ultimopharyngeal body

43. Pharyngeal Grooves
• During the fourth and fifth weeks, head and neck
region of the human embryo exhibit four pharyngeal
grooves or clefts on each side
• These grooves separate the pharyngeal arches
externally
• Only first pair persists as the external acoustic
meatus
• The other grooves normally obliterated with the
cervical sinus as the neck develops

44. Development of the Tongue
• The adult tongue is derived from embryonic processes arising
from the first three pharyngeal arches and a small
contribution from the fourth arch.
• The anterior two thirds of the adult tongue (the movable part) is
formed by two lateral swellings and a single one, the tuberculum
impar, all of which are derived from the first pharyngeal arch
44G.LUFUKUJA

45. Development of the Tongue…
• The posterior third (the fixed part or the root of the tongue) is
formed by an embryonic process, the hypobranchial eminence
or copula. This process is derived mainly from the second and
third pharyngeal arches with small part from the fourth
pharyngeal arch.
• The muscles of the tongue are derived from a different embryonic
source, namely the occipital myotomes.

46. Development of the Tongue

47. Development of the Tongue…
• The junction of the anterior 2/3 and the posterior 1/3 of the adult
tongue is marked by a V-shaped structure, the sulcus terminalis
and at its tip is a blind foramen, the foramen caecum. This site
marks the area from which an epithelial structure arise during
embryonic development and extend inferiorly to the anterior part
of the future neck where it forms the thyroid gland.

49. Thyroid Gland
• The thyroid gland appears as an
epithelial proliferation in the floor of the
pharynx between the tuberculum impar
and the copula at a point later indicated
by the foramen cecum . Subsequently
the thyroid descends in front of the
pharyngeal gut as a bilobed
diverticulum.
• During this migration, the thyroid
remains connected to the tongue by a
narrow canal, the thyroglossal duct.

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The Face
• The face is formed from 7 primordia surrounding the stomodeum
• Single frontonasal prominence -cranial boundary of the stomodeum
• Paired median nasal process
• Paired maxillary process
• Paired mandibularprocess
G.LUFUKUJA

51. Development of the Face…
• The Frontonasal prominence forms the forehead. The nasal
prominence is split into lateral and medial nasal processes by
formation of a nasal placode
• Thus a horseshoe-shaped nasal processes surrounds the nasal
placode, which undergoes apoptosis to form a depression; the
nasal pit. Initially, the maxillary and lateral nasal prominences
are separated by a deep furrow, the nasolacrimal groove.
• Ectoderm in the floor of this groove forms a solid epithelial cord
that detaches from the overlying ectoderm. After canalization, the
cord forms the nasolacrimal duct; its upper end widens to form
the lacrimal sac.

53. Intermaxillary segment
• As a result of medial growth of the maxillary prominences, the
two medial nasal prominences merge not only at the surface but
also at a deeper level. The structure formed by the two merged
prominences is the intermaxillary segment

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Anomalies
• Craniofacial: These are defects associated with tissue fusion.
Estimated 1/3 of all congenital defects are craniaofacial
• Facial Clefts - Anomalies associated with defective fusion of
Facial prominences
 1. Cleft lip - failure of maxillary prominence to fuse with
intermaxillary process
 2. Cleft palate - failure of the lateral palatine processes to fuse

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57. Thank you
57G.LUFUKUJA