4. Every individual spends the first 10
lunar months within the womb of its
mother. During this period it develops
from a small one-celled structure to
an organism having billions of cells.
Human face and jaws also develop
through a dynamic series of tissue
divisions, expansions, migrations,
fusions and involutions.
5. Embryology
Embryology is defined as the study of
the formation and development of embryo
from the moment of its inception up to the
time when it is born as an infant.
Subdivisions of embryology
Descriptive embryology
Comparative embryology
Experimental embryology
General embryology
Systemic embryology
6. Development of embryo
Prenatal
Period of ovum (conception till 7th or 8th day)
Embryonic period (2nd week to 8th week)
Period of fetus (3rd to 10th lunar month)
Postnatal
Neonatal
Infancy
Childhood
Adolescence
Maturity
7.
8. FORMATION OF GERM LAYERS
1- Fertilization
Fertilization of ovum takes place in
the ampulla of the uterine tube.
The fertilized ovum is a large cell.
At 2nd day, embryo is at 2-cell stage.
(approx. 30 hrs after fertilization)
9. 2- Cleavage
Cleavage is a series of mitotic divisions that
results in a rapid increase in number of cells,
blastomeres, which become smaller with each
division.
Compacted blastomeres divide to form a 16-cell
morula on 3rd day of fertilization.
As the morula enters the uterus on the fourth day
after fertilization, a cavity begins to appear, and
the blastocyst forms.
The inner cell mass, which is formed at the time
of compaction and will develop into the embryo
proper, is at one pole of the blastocyst.
The outer cell mass, which surrounds the inner
cells and the blastocyst cavity, will form the
trophoblast. The cells are still surrounded by
Zona Pellucida that helps in prevention of its
ectopic implantation.
10.
11. 3- Blastocyst Formation & Implantation
About the time the morula enters the uterine cavity, fluid
begins to penetrate through the zona pellucida into the
intercellular spaces of the inner cell mass.
Gradually the intercellular spaces become confluent, and
finally a single cavity, the blastocoele, forms. At this time,
the embryo is a blastocyst. Cells of the inner cell mass, now
called the embryoblast, are at one pole, and those of the
outer cell mass, or trophoblast, flatten and form the
epithelial wall of the blastocyst. The zona pellucida has
disappeared, allowing implantation to begin (at the end of 1st
week).
13. 4- Formation of germ layers (4th-8th week)
As the blastocyst develops further, it gives
rise not only to tissues and organs of the
embryo but also to a number of structures
that support the embryo and help it to
acquire nutrition. At a very early stage in
development, the embryo proper acquires
the form of three layered disc (also called
embryonic disc, embryonic area,
embryonic shield or germ disc).
15. The three layers that constitute this embryonic disc
are :
Endoderm (First germ layer to be formed)
Ectoderm (Second germ layer to be formed)
Mesoderm (Last germ layer to be formed)
Some cells of inner cell mass (of blastocyst)
differentiate into flattened cells that come to line its
free surface. These constitute the endoderm.
Remaining cells of inner cell mass become
columnar & constitute the ectoderm.
A space appears between ectoderm and
trophoblast which forms amniotic cavity. It gets
filled up with fluid called amniotic fluid.
16. Flattened endodermal cells spread and line through inside of
blastocystic cavity to form primary yolk sac.
Cells of trophoblast form mass of cells called Extra
Embryonic Mesoderm (E.E.M.) or primary mesoderm.
Cavities appear in E.E.M. called EXTRAEMBRYONIC
COELUM
Part inside of trophoblast and outside of amniotic cavity –
PARIETAL OR SOMATOPLEURIC EXTRAEMBRYONIC
MESODERM
Part outside the yolk sac VISCERAL OR
SPLANCHOPLEURIC EXTRAEMBRYONIC MESODERM
Chorion- Parietal E.E.M and overlying trophoblast is called
as chorion.
Amnion- Amniogenic cells forming the wall of amniotic cavity
excluding the ectodermal floor form the Amnion.
17.
18.
19. SECONDARY YOLK SAC
Yolk sac becomes much smaller with the
appearance of E.E coelom and is now called
secondary yolk sac. Endodermal cells become
cubical now.
PROCHORDAL PLATE
Near the margin of the disc cubical cells of
endoderm become columnar. This area is called
PROCHORDAL PLATE.
It determines the central axis of the embryo and
also helps to distinguish future head and tail ends.
20.
21. PRIMITIVE STREAK
Ectodermal cells lying along the central axis, near
the tail end begin to proliferate to form an
elevation that bulges into the amniotic cavity. It is
called as primitive streak. Cells in this area pass
sideways and push themselves between ectoderm
and endoderm to form 3rd layer called as intra-
embryonic mesoderm. It spreads throughout the
disc except in the region of prochordal plate. Here
ectoderm and endoderm remain in contact and will
form buccopharyngeal membrane.
The process of formation of primitive streak & of
intra embryonic mesoderm by the streak is termed
gastrulation.
23. GASTRULATION
FORMATION OF
NOTOCHORD
Cranial end of
primitive streak
becomes thickened.
This thickened part of
streak is called
Primitive Knot,
Primitive Node or
Henson’s node. A
depression appears in
its centre which is
known as blastopore.
24. Cells in the primitive knot multiply & pass
between ectoderm and endoderm reaching
up to caudal margin of prochordal plate.
These cells form notochordal process and
undergo several rearrangements to form
solid rod called as notochord.
As embryo enlarges notochord elongates
and comes to lie in the midline, in a
position to be later occupied by the
vertebral column. Most of it disappears but
part persists in the region of each
intervertebral disc as nucleus pulposus.
25. FORMATION OF NEURAL TUBE
Ectoderm above the notochord proliferates and
forms Neural plate.
Neural plate becomes depressed along the midline
as a result of which neural groove is formed. This
groove then becomes deeper. At the same time, 2
edges of neural plate come nearer each other and
fuse, thus converting groove into tube.
It will give rise to brain and spinal cord.
It is soon divisible into cranial enlarged part, that
forms brain and caudal tubular part which forms
spinal cord. This process of neural tube formation
is called as neurulation.
26.
27. FORMATION OF HEAD AND TAIL FOLDS
Embryonic disc develops lateral and head and tail
folds to form FOREGUT, MIDGUT AND
HINDGUT.
Part of yolk sac endoderm is incorporated into the
cranial end of embryo forming foregut.
Part of yolk sac endoderm incorporated into
caudal end forms the hindgut.
Intervening portion is the midgut which
communicates with yolk sac through yolk stalk.
29. DERIVATIVES OF VARIOUS GERM LAYERS
Derivatives of Ectoderm
Skin, including its pigments cells (from neural crest).
Mucous membrane of lips; cheeks, gums, part of the floor of the
mouth, part of the palate, nasal cavities and paranasal sinuses.
Anterior epithelium of cornea, epithelium of conjunctiva, epithelial
layers of ciliary body and iris.
Outer layer of tympanic membrane, epithelial lining of membranous
labyrinth including the special end organs.
Exocrine: Sweat glands, sebaceous glands, parotid, mammary
gland, lacrimal gland.
Endocrine: Hypophysis cerebri, adrenal medulla.
Hair, Nails.
Enamel of teeth.
Lens of eye; musculature of iris; vitreous humor.
Nervous system including all neurons, neuroglia and Schwann cells.
Pia-arachnoid.
Branchial cartilage.
30. Derivatives of Endoderm
Epithelium of part of the mouth, part of the palate, tongue,
tonsil, pharynx, oesophagus, stomach, small and large
intestines, and upper part of anal canal.
Epithelium of pharyngo-tympanic tube, middle ear, inner
layer of tympanic membrane, mastoid antrum and air cells.
Epithelium of respiratory tract.
Epithelium of gall bladder and extrahepatic duct system,
epithelium of pancreatic ducts.
Endocrine: Thyroid, parathyroid, thymus, islets of
Langerhans.
Exocrine: Liver, pancreas, glands in wall of gastrointestinal
tract, greater part of prostate (except inner glandular zone)
and its female homologous.
31. Derivatives of Mesoderm
All connective tissues including loose areolar tissue filling the
interstices between other tissues, superficial and deep
fascia, ligaments, tendons, aponeuroses, and the dermis of
skin.
Specialized connective tissues like adipose tissue, reticular
tissue, cartilage and bone.
Dentine of teeth.
All muscle – smooth, striated and cardiac- except the
musculature of the iris (ectoderm).
Heart, all blood vessels and lymphatics, and blood cells.
Substance of cornea; sclera, choroids, ciliary body and iris.
Dura mater, pia-arachnoid, microglia, etc.
Tympanic membrane is derived from both Ectoderm and
Endoderm.
32. FORMATION OF BRANCHIAL ARCHES
After the establishment of head folds, the foregut
is bounded ventrally by the pericardium, and
dorsally by the developing brain. Cranially, it is at
first separated from the stomatodaeum by
buccopharyngeal membrane. When the
membrane breaks down, the foregut opens to the
exterior through the stomatodaeum.
At this stage, the head is represented by the
bulging caused by developing brain, while
pericardium may be considered as occupying the
region of future thorax. The two are separated by
the stomatodaeum which is the future mouth. It is
apparent that neck is not present yet.
34. The neck is formed by the elongation of the
region between the stomatodaeum and the
pericardium. This is achieved partly, by a
‘descent’ of the developing heart. However,
this elongation is due mainly to the
appearance of a series of mesodermal
thickenings in the wall of the cranial most
part of the foregut. These are called as
pharyngeal, or branchial arches.
35. At this stage, the endodermal wall of the foregut is separated
from the surface ectoderm by a layer of mesoderm. Soon,
thereafter, the mesoderm comes to be arranged in the form
of six bars that run dorso-ventrally in the side wall of the
foregut.
Each of these bars grows ventrally in the floor of the
developing pharynx and fuses with the corresponding bar of
opposite side to form a pharyngeal or branchial arch.
In the interval between any two adjoining arches, the
endoderm extends outwards in the form of a pouch
(endodermal or pharyngeal pouch) to meet the ectoderm
which dips into this interval as an ectodermal cleft.
At first there are six arches. The fifth arch disappears and
only five remain.
Each pharyngeal arch contains a skeletal element
(cartilage that may later form bone), striated muscle
supplied by nerve of the arch, and an arterial arch
39. FATE OF ECTODERMAL CLEFTS
After the formation of the pharyngeal arches, the
region of the neck is marked on the outside by a
series of grooves, or ectodermal clefts. The dorsal
part of the first cleft (between the first and second
arches) develops into the epithelial lining of the
external acoustic meatus.
The pinna (or auricle) is formed from a series of
swellings that arise on the first and second arches,
where they adjoin the first cleft. The ventral part of
this cleft is obliterated.
40. FATE OF ENDODERMAL POUCHES
First Pouch: Its ventral part is obliterated by
formation of tongue. Its dorsal part receives a
contribution from the dorsal part of the second
pouch, and these two together form a diverticulum
that grows towards the region of the developing
ear. This diverticulum is called the tubotympanic
recess. The proximal part of this recess gives rise
to the auditory (pharyngotympanic) tube, and the
distal part to the middle ear cavity, including the
tympanic antrum.
42. Second Pouch
The epithelium of the ventral part of this pouch
contributes to the formation of tonsil.
The dorsal part takes part in the formation of the
tubotympanic recess.
Third Pouch
This gives rise to the inferior parathyroid glands,
and the thymus.
Fourth Pouch
This gives origin to the superior parathyroid
glands, and may contribute to the thyroid gland.
43. Fifth Or Ultimobranchial Pouch
A fifth pouch is seen for a brief period
during development. In some species it
gives rise to the ultimobranchial body. Its
fate in man is controversial.
It is generally believed to be incorporated
into the fourth pouch, the two together
forming the caudal pharyngeal complex.
The superior parathyroid gland arises from
this complex. The complex probably also
gives origin to the parafollicular cells of the
thyroid gland.
44. DEVELOPMENT OF FACE
Developing brain and pericardium form two
bulgings on the ventral aspect of embryo which is
separated by stomatodaeum. The floor of
stomatodaeum is formed by buccopharyngeal
membrane which separates it from foregut.
Mesoderm covering developing forebrain
proliferates and forms a downward projection
called frontonasal process. So finally face has to
develop from:
Frontonasal process.
Mandibular arch which gives a bud from dorsal
end. This is maxillary process which grows
ventromedially cranial to the main part of the arch;
now called mandibular process.
47. NASAL PLACODES
The ectoderm overlying the frontonasal
process shows bilateral thickenings above
the stomatodaeum called nasal placodes.
They soon sink to form nasal pits. The
edges of the pits get raised above the
surface.
Medial raised edge- median nasal
process
Lateral raised edge- lateral nasal process
48. LOWER LIP
The mandibular processes of
two sides grow towards each other
and fuse in the midline to form the
lower margin of stomatodaeum. The
fused mandibular processes give rise
to lower lip and lower jaw.
49. UPPER LIP
Each maxillary process now grows medially and fuses, first
with lateral nasal process and then with median nasal
process. The two fuse with each other. In this way nasal
processes are cut off from the stomatodaeum.
Maxillary process grows and frontonasal process becomes
much narrower and the two nares come closer.
Mesodermal bases of lateral part of the lip are formed from
maxillary process.
Overlying skin of lateral part of lip develops from ectoderm
covering this process
A mesodermal base of median part of the lip called philtrum,
is formed from frontonasal process. The ectoderm of the
maxillary process overgrows this mesoderm to meet that of
opposite side in the midline.
50. NOSE
Anterior nares are formed when nasal pits
are cut off from stomatodaeum by the
fusion of maxillary process with median
nasal process. Anterior nares approach
each other because of the frontonasal
process becoming narrower. Mesoderm
becomes heaped up in the median plane to
form prominence of the nose.
As the nose becomes prominent, anterior
nares come to open downwards instead of
forwards.
51. NASAL CAVITIES
The intervening tissue between the two nasal processes becomes
much thinned to form the nasal septum. The nasal cavities are
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
Extension of the nasal pits lead to formation of the nasal cavity.
Nasal pits deepen to form nasal sac which expand both dorsally
and caudally. Dorsal part of this sac is separated from
stomatodaeum by a thin bucconasal membrane which soon breaks
down.
The nasal sac has a ventral orifice that opens onto the face forming
anterior nares.
The dorsal orifice opens into stomatodaeum forming posterior
nares.
52. CHEEKS
After the formation of the upper & lower lips, the
stomatodaeum is very broad. In its lateral part, it is
bounded above by the maxillary process & below
by the mandibular process. These processes
undergo progressive fusion to form the cheeks.
NASOLACRIMAL DUCT
The fusion of the maxillary process not only occurs
in the region of lip but also extends up to medial
angle of eye. This line of fusion is marked by a
groove called naso-optic furrow. A strip of
ectoderm gets buried along this furrow and gives
rise to nasolacrimal duct.
53. EYE
On the ventral side of developing forebrain lateral
and cranial to nasal placodes develops an
ectodermal thickening called lens placode. It sinks
below the surface and is cut off from surface
ectoderm. The developing eyeball produces a
bulging which are first directed laterally and then
lie in angle between maxillary process and lateral
nasal process.
Eyelids are derived from folds of ectoderm and by
mesoderm enclosed within the folds.
54. EXTERNAL EAR
It is formed from the dorsal part of the first
ectodermal cleft and mesodermal thickenings
(called tubercles or hillocks) which appear on the
mandibular and hyoid arches where they adjoin
this cleft.
Pinna is formed by fusion of these thickenings.
When first formed, pinna lies caudal to the
developing jaws. It is pushed upward and
backward to its definitive position due to great
enlargement of the mandibular processes.
55.
56. DEVELOPMENT OF FACIAL SKELETON
The skeletal system develops from the
mesodermal germ layers during 3rd week of
development. Somites form on each side of neural
tube. It becomes differentiated into sclerotome,
dermatome, myotome.
At the end of 4th week, the sclerotome cells
become polymorphous and form loosely woven
tissue known as MESENCHYME or embryonic
connective tissue.
The characteristic feature of mesenchymal cells is
that, it can migrate and differentiate into many type
of cells. Such as fibroblasts, chondroblasts,
osteoblasts. Neural crest cells in the head region
differentiate into mesenchyme and participate in
the formation of bones of the face.
57.
58. MEMBRANOUS NEUROCRANIUM
(DESMOCRANIUM)
The sides of roof of skull develop from
mesenchyme investing the brain and undergo
membranous ossification.
As a result a number of flat membranous bone
are formed which are characterized by the
presence of needle like bone spicules.
The membranous bones enlarges by apposition
of new layers on the outer surface and by
simultaneous osteoclastic resorption from the
inside.
59. CARTILAGENOUS NEUROCRANIUM
This part of the skull consists initially of
number of separate cartilages which fuse
and ossify by endochondral ossification,
Example- the base of the skull.
CARTILAGE FORMING STRUCTURE
Parachondral Cartilage
& Occipital Sclerotomes Occipital Bone
Hypophyseal Cartilage Body of Sphenoid
Trabeculae Cranii Ethmoid bone
61. VISCEROCRANIUM
It consists of bone of face and is formed mainly by
cartilages of first two pharyngeal arches.
Dorsal portion of the first arch (maxillary process)
gives rise to maxilla, zygomatic bone and part of
temporal bone.
The ventral portion is known as Meckel’s cartilage
or mandibular process. The mesenchyme around
Meckel’s cartilage condenses and ossifies by
intramembranous ossification, to give rise to
mandible. Meckel’s cartilage disappears except in
sphenomandibular ligament. The dorsal tip of
mandibular process along with that of the second
arch give rise to incus, malleus and stapes.
At first face is small in comparison with
neurocranium. This is caused by virtual absence of
paranasal sinuses and small size of the bones.
63. ORIGIN OF BONES OF HEAD & NECK
Endochondral
Conversion of mesenchymal connective tissue first into a cartilage
and then bone is called as endochondral ossification. Examples of
bones formed by endochondral ossification are-
Squamous & basilar part of Occipital bone except supranuchal
squamous part.
Occipital condyle
Sphenoid (Medial pterygoid plate, lesser wing of sphenoid, portion
of greater wing of sphenoid- alisphenoid cartilage, anterior &
posterior part of sphenoid body.
Ethmoid
Temporal (Petrous and Styloid).
Condyle of mandible.
Ear ossicles.
Hyoid
64. Intra-membranous
Conversion of mesenchymal connective tissue, usually
in membranous sheaths, directly into osseous tissue is
known as intramembranous ossification. Examples of bones
formed by intramembranous ossification are-
Supranuchal squamous part of occipital bone.
Sphenoid- Greater wing, lateral pterygoid plate.
Temporal- squamous & tympanic.
Body of mandible.
Nasal, Lacrimal, Vomer, Frontal, Parietal.
Maxilla, Palatine,
Zygomatic Bones
65. CENTRES OF OSSIFICATION
In both types of bone formation,
ossification begins at definite points known
as Centres of Ossification.
A primary centre of ossification is first to
appear mostly before birth, which may be
followed by
one or more secondary centres, generally
postnatally, all of which coalesce into a
single bone.
66. MAXILLA
A primary intramembranous ossification centre
appears for each maxilla in 8th week at the termination of
infraorbital nerve just above canine tooth.
Secondary cartilages appear in the end of 8th week in the
region of zygomatic and alveolar process that ossify and
fuse with primary intramembranous centre.
2 intramembranous premaxillary centers appear anteriorly
on each side and fuse with primary maxillary centre
Maxilla has different units on which its growth depends
Alveolar unit –teeth
Nasal unit- septal cartilage
Orbital unit –eyeball
Pneumatic unit-maxillary sinus expansion
67. MANDIBLE
First structure to develop in the primordium of the lower jaw
is the mandibular division of trigeminal nerve.
Mandible is derived from ossification of an osteogenic
membrane formed from ectomesenchymal condensation at
5-6th weeks of development.
Cartilage of first arch is Meckel’s cartilage.
A single ossification centre for each half of mandible arises
in 6th week at the bifurcation of inferior alveolar nerve and
artery into mental and incisive branches.
Ossifying membrane which is located lateral to Meckel’s
cartilage ossifies dorsally and ventrally to form body and
ramus of the mandible.
Ossification stops dorsally at site that will later become
lingula.
68.
69. Core of Meckel’s cartilage diverges dorsally to end
in tympanic cavity of middle ear where it ends as
ear ossicles- malleus and incus.
Major portion of Meckel’s cartilage disappears. A
part transforms into sphenomandibular ligament
and anterior malleolar ligament.
Secondary cartilages appear between 10 and 14
week of intra uterine life to form head of condyle,
part of coronoid and mental protuberence.
Coronoid cartilage later becomes incorporated into
ramus and disappears before birth.
Condylar cartilages appear during 10th week of
development as primordia of future condyle.
70. PARANASAL SINUSES
Sinuses appear as diverticula’s from
the nasal cavity. The diverticula’s
invade the bone after which they are
named.
71. PALATE
The palate is formed by the contributions of the :
Maxillary process
Palatal shelves given off by the maxillary process
Frontonasal process which gives rise to the premaxillary
region while the palatal shelves form the rest of the palate
From each maxillary process a plate like shelf grows
medially called as palatal process. Each palatal
process fuses with each other in the midline and also
with the posterior margin of primitive palate (which is
formed from the frontonasal process).
The medial edges of palatal processes fuse with the
lower edge of the nasal septum thus separating two
nasal cavities from each other and from the mouth.
Medial growth of the palatal shelves & their union is
prevented by the presence of the tongue, thus the
palatal shelves grow vertically downwards initially.
During the 7th week of intrauterine life, a
transformation in the position of the palatal shelves
occurs i.e from a vertical to a horizontal position.
73. The connective tissue of the palatal
shelves intermingle with each other
resulting in their fusion around the 8 ½
weeks of intra-uterine life
Mesoderm in the palate undergoes
intramembranous ossification to form the
hard palate.
Ossification does not extend into posterior
most portion which remains as the soft
palate.
74. TEMPOROMANDIBULAR JOINT
TMJ develops initially from widely separated
temporal and condylar blastema that grows
towards each other.
TMJ has a fibrous tissue rather than hyaline
cartilage on the articular facets of temporal fossa
and condyle.
Between 10th to 12th week, mesenchyme
between growing secondary cartilage of condyle
and temporal bone differentiate into fibrous tissue.
During 12th week 2 clefts develops in the
interposed vascular fibrous connective tissue
forming two joint cavities and thereby defining
intervening articular disc.
76. Compression of central portion of articular
disc occurs as it takes biconcave shape.
Tissue of disc becomes continuous with
tendon of lateral pterygoid anteriorly.
Posteriorly it gets attached to portion of
Meckel’s cartilage which differentiates into
malleus.
A condensation of mesenchyme forms the
analogue of the joint capsule thereby
isolating the joint with its synovial
membrane from its surrounding tissues.
77. TONGUE
Tongue develops in relation to the pharyngeal arches in the
floor of developing mouth.
Medial most part of mandibular arches proliferates to form 2
lingual swellings. Two lingual swellings are separated by a
median swelling called tuberculum impar.
Anterior 2/3rd of tongue is formed by fusion of:
Two lingual swellings
Tuberculum impar
Midline swelling seen in relation to medial ends of 2nd, 3rd,
and 4rth arches form hypobranchial eminence. This shows
subdivision into a cranial part (related to 2nd and 3rd arches)
called copula, and a caudal part which forms epiglottis.
78.
79.
80. Posterior 1/3rd is formed from cranial part of
hypobranchial eminence.
Posterior most part is derived from fourth arch.
Musculature of the tongue develops from occipital
myotomes.
Initially epithelium is single layered but later
becomes stratified and papillae become evident.
Taste buds are formed in relation to terminal
branches of innervating nerve fibers.
81.
82. NERVE SUPPLY OF TONGUE
Sensory
Lingual nerve for anterior two –third
Glossopharyngeal nerve for posterior one –third
Motor
All the muscle except palatoglossus are supplied by
hypoglossal nerve
Palatoglossus is supplied by cranial part of accessory
nerve
Taste
Chorda tympani nerve for anterior two –third
Glossopharyngeal nerve for posterior one –third
83. Anterior two–third part of tongue Develops
from two lingual swellings & tuberculum impar
of first branchial arch. Supplied by lingual
nerve and Chorda tympani nerve
Posterior one–third part of tongue Develops
from hypobranchial eminence of third branchial
arch. Supplied by glossopharyngeal nerve.
Posterior most part Develops from fourth
branchial arch. Supplied by vagus nerve
84. SALIVARY GLANDS
Oral epithelium buds invade the underlying mesenchyme.
All parenchymal tissue of the glands arises from proliferation
of oral epithelium that may be either ectodermal or
endodermal in origin.
Stroma of glands originates from mesenchyme that may be
either mesodermal or neural crestal in origin.
Following the initial bud formation, there is elongation of
epithelial cell cords to form the main duct primordia,
branching produces arborization and terminal bulbs. It is first
solid and later canalises
It branches repeatedly to form duct system. Terminal parts of
the duct system develop into secretory acini
Parotid arises in relation to line along which maxillary and
mandibular processes fuse to form cheeks and is considered
ectodermal
Submandibular and sublingual glands arise in relation to
linguogingival sulcus and are considered endodermal in
origin.
85. TONSILS
2nd pharyngeal pouch gives rise to
palatine tonsil.
Pharyngeal and lingual tonsils develop in
the mucosa of posterior wall of the pharynx
and root of tongue.
Lateral extension of lymphoid tissue
posterior to the opening of auditory tube
forms tubal tonsil.
Invasion of lymphoid tissue into the
palatine, posterior pharyngeal and lingual
tonsillar region takes place during 5th
month I.U.L.
87. DEVELOPMENTAL ANOMALIES OF FACE
Formation of face involves fusion of diverse components. This
fusion is often incomplete and gives rise to various abnormalities.
1. HARE LIP
Upper lip of hare has normally a cleft hence the term hare lip is
used for such defects.
When one or both the maxillary processes do not fuse with medial
nasal process, this gives rise to defects in upper lip.
Defective development of frontonasal process give rise to midline
cleft of upper lip
When two mandibular processes do not fuse with each other lower
lip shows defect in midline.
2. OBLIQUE FACIAL CLEFT
Nonfusion of maxillary and lateral nasal processes give rise to cleft
running from medial angle of eye to the mouth. Thus nasolacrimal
duct is not formed.
(Various genes and loci have been identified as responsible for
orofacial clefts. These include 1q, 2p, 4q, 6p, 14q, 17q, and 19q)
89. 3. MACROSTOMIA
Inadequate fusion of maxillary and
mandibular process leads to
macrostomia
4 MICROSTOMIA
Too much fusion may lead to
microstomia
90. 5. NOSE
Nose may be bifid or one half may be absent.
Rarely nose forms a cylindrical projection or
proboscis.
6. MANDIBULOFACIAL DYSOSTOSIS
Entire first arches may remain underdeveloped on
one or both sides, affecting the lower eyelid,
maxilla, mandible or external ear. The prominence
of cheek is absent and ear may be displaced
caudally and ventrally. This condition is
MANDIBULOFACIAL DYSOSTOSIS.
91. 7. FACIAL HEMI HYPERTROPHY
One half of the face may be underdeveloped
leading to facial hemi atrophy or overdeveloped
leading to facial hemi hypertrophy.
8. RETROGNATHIA
Mandible may be small as compared to rest of
face resulting in a receding chin (retrognathia).
9. CONGENITAL TUMORS
These may be present in face. They may
represent attempt at duplication of some parts.
92. 10. HYPERTELORISM
Eyes may be widely separated
(hypertelorism)
11. DOUBLE LIP
Lips may show congenital pits or
fistulae. Lips may be double
93. ANOMALIES OF NASAL CAVITY
There may be atresia of cavity at the anterior
nares or at the posterior nares or in the cavity
proper. This may be unilateral or bilateral.
There may be absence of nasal passages.
Congenital defects in the cribriform plate of the
ethmoid bone may lead to a communication
between cranial cavity and nose.
Nasal septum may be absent or may be deviated.
Nasal cavity may communicate with the mouth.
94. ANOMALIES OF TONGUE
Tongue may be too large (macroglossia) or too small
(microglossia).
Very rarely tongue may be absent (aglossia).
Apical part of tongue may be attached to floor of mouth by an
overdeveloped frenulum.condition is ankyloglossia or tongue tie.
Occasionally tongue may be attached to palate (ankyloglossia
superior).
A red, rhomboid shaped smooth zone may be present on tongue in
front of foramen caecum because of persistence of tuberculum
impar (median rhomboid glossitis).
Thyroid tissue may be present in the tongue either under mucosa or
within the muscles.
Remnants of thyroglossal duct may form cysts at the base of
tongue (Thyroglossal tract cyst).
Surface of tongue may show fissures (fissured tongue).
95. ANOMALIES OF LIPS
Congenial lip and commissural pits and
fistulae
Double lip
Cleft lip and palate
Chelitis glandularis
Chelitis granulomatosa or meischer’s
syndrome
Hereditary intestinal polyposis or peutz
jeghers syndrome
96. DEVELOPMENTAL DISTURBANCES OF
SALIVARY GLANDS
Aplasia
Xerostomia
Hyperplasia of palatal glands
Artesia
Aberrancy
Developmental lingual mandibular salivary
gland depression (static cavity or Stafne
cyst)
