Bones of the Pelvic Girdle and Lower Extremity

And Lower Extremity
Bones of the Pelvic Girdle

Introduction

After folding, the 2ry yolk sac inside the embryo
.gives rise to : Fore gut -Mid gut – hind gut Oral
membrane
: The fore gut is divided into


Amniotic
cavity
Gut

Before folding
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

Cloacal
membrane
Yolk sac

Amniotic cavity

Foregut

Midgut
Hindgut

Stomodeum

Vitello-intestinal
duct

Allantois Cloacal
membrane
Connecting stalk

After folding

.b. Caudal part : begins distal to the laryngotracheal groove
It gives rise to: esophagus-stomach- part of duodenumliver-biliary system –pancreas.
Prof. Mohamed A. Autifi

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












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.

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.


Nerve supply of the pharyngeal arches


It is derived from the
hindbrain (pons and M.O)



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.






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.

Development of Pharyngeal arches


Cartilages






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 (swelling) and a caudal mandibular
process (swelling).
Each process contains a central cartilaginous element
(the maxillary known as palato-pterygo-quadrate cartilage
and the mandibular known as Meckel's cartilage)
surrounded by a mesenchymatic tissue.


Arch
First arch
(mandibular
arch)
Consists of
maxillary
process
and
mandibular
process

Skeletal
Muscular
Derivatives
Derivatives
Maxillary
1.Muscles of
process
Mastication
gives rise to:
1.Maxilla
2.Tensor
2.Zygomatic bone
palati
3.Squamous part
of temporal bone
3.Tensor
Mandibular
tympani
process
differentiates
into :
4. Mylohoid
1.Malleus
2.Incus
5. Anterior
3.Anterior
belly of
ligament of
digastric
malleus
4.Sphenomandibular
Prof. Mohamed. A. Autifi
ligament

Vascular
Element

1. Maxillary
artery

Nereve

Mandibular
nerve (V)

Arch
Second arch
(Hyoid arch)

Skeletal
Derivatives

Muscular
Derivatives

Reichert’s
cartilage:
Differentiates
into:
1.Stapes
2.Styloid
process
3.Stylohyoid
ligament
4.Lesser horn
of the hyoid
bone
5.Upper part of
body of hyoid
bone

Vascular
Element

1. Muscles of Stapedial
the scalp artery
and face
(caroticotympanic br.
2. Platysma
of ICA)
3. Stylohyoid
4. Stapedius
5. Posterior
belly of
digastric



Nereve

Facial nerve
(VII)

Arch
Third arch

Skeletal
derivatives

1. Greater horn of Stylopharyngeus
hyoid bone
2. Lower part of
body of hyoid bone

Fourth arch Thyroid cartilage

Sixth arch

Muscular
derivatives

Cricothyroid

Rest of Cartilages 1. Other intrensic
of the larynx
muscles of larynx
except
epiglottis:
2. Constrector
-Cricoid,
muscles of pharynx
-Arytenoid,
except
-Corniculate
Stylopharyngeus
and
-Cuneiform.
3. Muscles of
NB. The epiglottis palate except
develops from tensor palati
mesenchyme in
hypobrancheal

Vascular
Element

Nereve

1. I.C.A
2. C.C.A

Glossopharyngeal
nerve (IX)

1. Arch of aorta
on left side
2. Subclavian A
on right side

Superior
laryngeal nerve
(X)

1. Pulmonary A
on each sides
2. Ductus
arteriosus
on left side

Recurrent
laryngeal nerve
(X)

More details about cartilages
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

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

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


Derivatives of The fourth and sixth Pharyngeal
Arch Cartilages
• 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

Muscular component


Development of Pharyngeal pouches and clefts


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

•

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


Second pouch
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


Third pouch

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


Fourth pouch
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

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.

Congenital anomalies

Lateral cervical cysts and fistulas
( (Branchial cyst & Branchial fistula


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.

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.

6. Ectopic Thymic Tissue:

Thymus gland lies in the neck.

7. Ectopic Parathyroid:

Inferior parathyroid may present at bifurcation of
Common carotid artery.


Thank you
for attention


Derivatives of
pharyngeal floor

The pharyngeal floor is
formed by fusion of
ventral parts of the
arches & pouches: It
gives rise to:
A. Thyroid gland.
B. Tongue.
C. Lower respiratory
system.


Development of the thyroid gland






Thyroid primordium appears as a
median endodermal proliferation in
the floor of the pharynx between
tuberculum impar and hypobranchial
emenence (the site is indicated by
foramen caecum in adult)
This thickening is invaginated to
form a bilobed divertaculum which
descend ventral to the developing
hyoid bone then ventral to the
developing larynx.
It remains connected to the dorsum
of the tongue by the thyroglossal
duct


1

3

2
4





The thyroid gland reaches its final position
by the 7th week and begins to function at the
end of the 3rd month .
The endodermal cells of the thyroglossal duct
form the thyroid follicles which secrete
thyroxine and triiodothyronine hormones.




The ultimobranchial body forms parafollicular
C cells which secrete calcitonin.
The mesoderm forms the true capsule and
connective tissue septa.






Fate of the thyroglossal duct:
The part of the duct between hyoid bone and isthmus of
the gland gives rise to pyramidal lobe and levator
glandulae thyroidae
Above the hyoid bone the duct degenerate completely.


Congenital Anomalies:
1. Agenesis:  congenital
hypothyroidism
2. Ectopic (aberrant)
thyroid: Lingual,
sublingual, or thoracic
3. Thyroglossal cyst: In
midline of neck,
common at
lingual,
supra-, retro- or
infra-hyoid sites
4. Thyroglossal sinus:
Due to rupture of
thyroglossal cyst


Thyroglossal cyst


Development of Tongue


A. The mucous membrane


Anterior 23:
arises from 3 swelling derived from the ventral
parts of both 1st pharyngeal arches as follows:

•2
•1





lateral lingual swellings and
median swelling “tuberculum impar”

Posteror 13:
developed from the upper half of
hypobranchial eminince”
The post.13 fuses with the ant.23 along
a v-shaped sulcus terminalis.

B. The muscles of the tongue


Derived from the occipital myotomes that

migrate to the developing tongue taking with
it their nerve supply (hypoglossal nerve)
 Some of the tongue muscles are
differentiated in situ.
 NB. At first the tongue is fused with the
floor of the pharyngeal gut. Later on linguogingival groove appears on either side and
frees the tongue from the floor of the mouth


Lingual papillae & taste buds:
Vallate & foliate papillae appear first in
relation to branches of IX n
Fungiform & filiform papillae appear later near
fibers of chorda tympani.
-All papillae soon develop taste buds
Lymphoid follicles aggregate under mucosa of
post 1/3 of tongue ➪ lingual tonsil

Congenital Anomalies:
1. Ankyloglossia (tongue-tie): Frenulum of tongue extends
to its tip. Prevents movements & hinders proper speech
2. Macroglossia: Large tongue, due to lymphangioma or
muscular hypertrophy
3. Microglossia
4. Cleft tongue: Incomplete fusion of lingual swellings ➪
median groove/cleft, does not extend to tongue tip
5. Bifid tongue: Cleft extends to tip
6. Congenital cysts & fistulae: Remnants of thyroglossal
duct

Tongue tie
Microglossia

Macroglossia


Bifid Tongue

Tongue tie


Bones of the Pelvic Girdle and Lower Extremity

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