1. EMBRYOLOGY
BY
Dr. THAAER MOHAMMED DAHER ALSAAD
SPECIALIST IN GENERAL SURGERY
M.B.Ch.B. (MBBS) F.I.B.M.S. )Ph.D.)
SENIOR LECTURER
IMS MSU
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11. TOPICS
• HIGHLIGHTS.
• INTRODUCTION.
• DEVELOPMENT OF THE FACE/ LIPS, NOSE,
CHEECHS, EYE, EXTERNAL EAR.
• DEVELOPMENT OF THE PALATE.
• ANOMALIES.
• TIMETABLE.
12. TIMETABLE OF SOME EVENTS DESCRIBED IN THIS CHAPTER
Age Developmental events
4th week The frontonasal, maxillary and mandibular
(28th day) processes can be identified.
Lens and nasal placodes are also present.
5th week (31 The nasal pits are established.
to 35 days)
6th week Tubercles of the development of pinna begins to be
formed.
On each side, palatal process appears from the maxillary
process.
7th week Eyelid established.
Maxillary processes fuse with medial nasal process.
8th week Eye shift from lateral to medial position.
Bucconasal membrane ruptures.
10th week The palatal processes and nasal septum fuse
with each other.
13. HIGHLIGHTS
• STOMATODIUM = future mouth.
• FRONTONASAL PROCESS + Rt. AND Lt. MANDIBULAR ARCHES.
• THE MANDIBULAR ARCH divides into a maxillary process and a
mandibular process.
• The Lt. and Rt. Mandibular processes meet in the midline
and fuse to form the lower and upper jaw.
• The upper lip is formed by fusion of the frontonasal process
with the Rt. And Lt. maxillary processes./ hare lip (failure to fuse).
• The cheeks are formed by fusion of the posterior parts of the
maxillary and mandibular processes.
14. HIGHLIGHTS (continue)
• The nose is derived from the frontonasal process.
• The nasal cavity is formed as follows;
• An ectodermal thickening (nasal placode) appears over the
frontonasal process.
• The placode gets depressed below the surface to form the
nasal pit.
• The nasal pits enlarged to form the nasal cavity.
• Paranasal sinuses appear as outgrowths from the nasal cavity.
• The palate is formed by fusion of the three components;
• Rt. And Lt. palatal processes (arising from the maxillary process) and
the primitive palate (derived from the frontonasal process).
• Deficiency in fusion leads to various form of cleft palate.
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16. INTRODUCTION
• Brain and heart bulging are separated by the stomatodaeum.
• The floor of the stomatodaeum is formed by the
buccopharyngeal membrane.
• Soon, mesoderm covering the developing forebrain proliferates,
and forms a downward projection (frontonasal process) that
overlaps the upper part of the stomatodaeum.
• Pharyngeal arches are in very close relationship to the
stomatodaeum.
• The face is derived from the following structures that lie around
the stomatodaeum:
1. The frontonasal process.
2. The 1st pharyngeal arch on each side.
17. INTRODUCTION
• The mandibular arch forms the lateral wall of the stomatodaeum.
• This arch gives off the maxillary process.
• Maxillary process grows ventro-medially cranial to the main part of
the arch (mandibular process).
• The ectoderm of the frontonasal process shows BILATERAL
LOCALIZED THICKENINGS (the nasal placodes) that are situated
above the stomatodaeum.
• The placodes form nasal pits.
• The pits are continuous with the stomatodaeum below.
• The edges of each pit are raised above the surface as medial and
lateral nasal process.
18. DEVELOPMENT OF THE FACE
LOWER LIP
• The mandibular processes of the two sides grow
toward each other and fuse in the midline.
• They form the lower margin of the
stomatodaeum (mouth).
• The fused mandibular processes give rise to the
lower lip, and the lower jaw.
19. DEVELOPMENT OF THE FACE
UPPER LIP
1. The maxillary process fuses with the lateral and then with medial nasal
process. The lateral and medial process fuse with each other, forming
the external nares (nasal pits) and are cut off from the stomatodaeum.
2. The two external nares come closer together (maxillary process grows
and the frontonasal process becomes much narrower).
3. The stomatodaeum is bounded above by the upper lip
which derived as follows;
1. Maxillary process forms the mesoderm of the lateral part of the
lip. The ectoderm of the maxillary process gives rise to the
overlying skin.
2. Mesoderm of the median part (philtrum) is derived from the
frontonasal process. But the ectoderm is derived from the
maxillary processes and meet in the midline. Therefore, the
skin of entire upper lip is innervated by maxillary nerve.
4. The muscles of the face are derived from the 2nd
branchial arch and are supplied by the facial nerve.
20. DEVELOPMENT OF THE FACE
NOSE
• The nose receives contribution from the frontonasal process,
and from the medial and lateral nasal processes of the RT.
And Lt. sides.
• Nasal pits – nares --- cut off from the somatodaeum.
• External nares approach each other. (due to the frontonasal
process becomes narrower and its deep part forms the nasal septum).
• Mesoderm becomes heaped up in the median plane to
form the prominence of the nose.
• Simultaneously, a groove appears between the region of the nose
and the bulging forebrain.
• As the nose becomes prominent, the external nares come to open
downwards instead of forwards. (the external form of the nose is
established).
21. DEVELOPMENT OF THE FACE
CHEEKS
• After the formation of the upper and lower lips, the stomatodaeum
is very broad.
• In its lateral part, it is bounded above by the maxillary process
and below by the mandibular process.
• These processes undergo progressive fusion with each other to form the
cheeks.
• The maxillary process fuses with the lateral nasal process in the region of
the lip and extends from the stomatodaeum to the medial angle of the
developing eye.
• This line of fusion is called NASO-OPTIC FURROW or NASOLACRIMAL
SULCUS.
• A STRIP OF ECTODERM becomes buried along this furrow and gives
rise to the nasolacrimal duct.
22. DEVELOPMENT OF THE FACE
EYE
• The region of the eye is first seen as ectodermal thickening, the
lens placode.
• Lens placode appears on the ventro-lateral side of the
developing forebrain.
• Lens placode is lateral and cranial to the nasal placode.
• LENS PLACODE sinks below the surface and cut off from the surface ectoderm.
• The developing eye produces bulging in this situation. (bulgings
of eyes first directed laterally, and lie in the angles between the
maxillary processes and the lateral nasal processes). With the
narrowing of the frontonasal process they come to face forwards.
• The eyelids are derived from folds of ectoderm that are formed
above and below the eyes, and mesoderm enclosed within the
folds.
23. DEVELOPMENT OF THE FACE
EXTERNAL EAR
• The external ear is formed around the dorsal part of the 1st
ectodermal cleft.
• A series of mesodermal thickenings appear on the
mandibular and hyoid arches where they adjoin this cleft.
• The pinna is formed by fusion of these thickenings.
• When first formed, the pinna lies caudal to the developing
jaw.
• It is pushed upwards and backwards to its definitive
position due to the great enlargement of the mandibular
process.
• If the mandibular process fails to enlarge, the ears remain
low down.
24. DEVELOPMENTAL ANOMALIES OF THE FACE (skip)
1. Hare lip.
2. Oblique facial fissure.
3. Macrostomia X Microstpmia // lateral facial cleft.
4. Bifid nose // proboscis +/- cyclops.
5. Mandibulofacial dystosis, (1st arch syndrome or Teacher
Collins syndrome).
6. Hemiface Underdeveloped/ overdeveloped.
7. Retrognathia ??? // Agnathia.
8. Congenital tumours.
9. Hypertelorism.
10. Double lip. / congenital pits or fistula.
25. DEVELOPMENT OF THE FACE
NASAL CAVITY
• The nasal cavities are formed by extension of the nasal pits.
• The medial and lateral nasal processes fuse and form a partition
between the nasal pits and the stomatodaeum.
• This partition is called the primitive palate. (frontonasal process
derivative).
• Nasal pits deepen to form nasal sacs.
• Nasal sac posteriorly is separated from the stomatodaeum by
buccopharyngeal membrane (nasal fin).
• Nasal fin breaks soon.
• Nasal sac has a ventral orifice on the face called the anterior or
external nares.
• and a dorsal orifice opens into the stomatodaeum called the
primitive posterior nasal aperture.
26. DEVELOPMENT OF THE FACE
NASAL CAVITY (continue)
• The two nasal sacs are first widely separated from each
another by frontonasal process.
• Nasal cavities enlargement + narrowing of the frontonasal
process (=) bring cavities closer together.
• The intervening tissue forms the nasal septum.
• Ventral part of the nasal septum is attached below
to the primitive palate.
• Nasal septum posteriorly is at first attached to the
bucconasal membrane, but on disappearance of this
membrane it has free lower edge.
27. DEVELOPMENT OF THE FACE
NASAL CAVITY (continue)
• The nasal cavity is separated from the mouth by the
development of the palate.
• The lateral wall of the nose is derived, on each side, from the
lateral nasal process.
• The nasal conchae appear as elevations on the lateral wall
of each nasal cavity.
• The original olfactory placodes form the olfactory
epithelium that lies in the roof, and adjoining parts
of the walls, of the nasal cavity.
28. Anomalies of the Nasal Cavity
1) Atresia / uni or bilateral /? Absence.
2) Congenital communication between the
cranial cavity and the nose.(cribriform plate
defects).
3) Deflected nasal septum. /// absent.
4) Communicates with the mouth.
29. In 1961, a twelve man Soviet crew was building a new base in the Antarctic.
Mindful that being trapped in sub-zero temperatures for months on end
required a medical professional to be on hand, one doctor had been
assigned to the team. So what happens when the only man capable of
performing surgery comes down with a severe case of appendicitis?
He does what any reasonably minded person would do.
Performs an appendectomy…on himself
30. DEVELOPMENT OF THE FACE
PARANASAL SINUSES
• Paranasal sinuses appear as diverticula from the nasal cavity.
• The diverticula invade the bones after which they are named.
• The maxillary and sphenoidal sinuses begin to develop before birth.
• The other sinuses develop after birth.
• Enlargement of the sinuses associated with the overall
enlargement of the facial skeleton including the jaws.
• This provides spaces in the jaws for growth and eruption
of teeth.
• Growth of facial skeleton is responsible for the gradual
change in looks of a baby.
31. DEVELOPMENT OF THE PALATE
• The maxillary process form the upper lip.
• Maxillary process extends backwards on either sides of
the stomatodaeum.
• The palatal process grows medially from the maxillary process.
• The palate forms from three components:
1. The two palatal processes, and
2. The primitive palate formed from the frontonasal process.
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33. DEVELOPMENT OF THE PALATE (continue)
• The definitive palate is formed by the fusion of three parts as follows:
1) Fusion of each palatal process with the posterior margin of the primitive palate.
2) Two palatal processes fuse in the midline. (fusion begins anteriorly and
proceeds posteriorly).
3) Fusion of the medial edges of the palatal processes with the free lower edge of
the nasal septum. (thus separating nasal cavities from each other and from the
mouth).
4) At later stage, the mesoderm in the palate undergoes
intramembranous ossification to form the hard palate.
The ossification does not extend to the posterior portion, which
remains as the soft palate.
The part of palate derived from the frontonasal process forms the
premaxilla, which carries the incisor teeth.
34. Cleft Palate
• Defective fusion of the various components of the
palate gives rise to clefts in the palate.
• Clefts vary considerably in degree.
• Clefts may be unilateral or bilateral.
• Clefts of the palate that extend to its anterior end
are associated with harelip, (as both the upper lip and
the palate are formed by fusion of the maxillary processes
with the frontonasal process).
• Clefts of the palate result in anomalous
communicating between the mouth and the nose.
35. TIMETABLE OF SOME EVENTS DESCRIBED IN THIS CHAPTER
Age Developmental events
4th week The frontonasal, maxillary and mandibular
(28th day) processes can be identified.
Lens and nasal placodes are also present.
5th week (31 The nasal pits are established.
to 35 days)
6th week Tubercles of the development of pinna begins to be
formed.
On each side, palatal process appears from the maxillary
process.
7th week Eyelid established.
Maxillary processes fuse with medial nasal process.
8th week Eye shift from lateral to medial position.
Bucconasal membrane ruptures.
10th week The palatal processes and nasal septum fuse
with each other.
