Pharyngeal arches & pouches

1. Development of Pharyngeal Arches & Pouches
Dr. Prabhakar Yadav
Associate Professor
Department of Human Anatomy
B.P. Koirala Institute of Health Sciences

2. After establishment of head fold,
foregut is bounded ventrally by
pericardium & dorsally by developing
brain.
Foregut is initially separated from
stomatodeum by buccopharyngeal
membrane, when it breaks down,
foregut opens to exterior.
Developing brain & pericardium are
seperated by stomatodeum -
………………………

3. Elongation of region between stomatodaeum &
pericardium forms- Neck.
Elongation is due to series of mesodermal
thickening in the wall of cranial most part of foregut
- pharyngeal / branchial arches - provide support to
lateral & ventral of wall of primitive pharynx.

4. •Before appearance of pharyngeal arches endoderma of foregut is separated form ectoderm by
mesoderm.
•Mesoderm form thickening in the form of six bars that runs dorsoventrally in the floor of developing
pharynx and fuse with corrosponding bar of opposite side to form pharyngeal arch.
•Initially there are six arches. The fifth arch is small and rudimentary, and soon disappears. Pharyngeal
arches are numbered craniocaudally as 1, 2, 3, 4, and 6.

5. Between two adjoining arches,
endoderm extend outward in the form
of –endodermal or branchial or
pharyngeal pouch.
Between two adjoining arches,
ectoderm invaginate inward in the
form of – ectodermal cleft.
Between two adjoining arches where
pharyngeal cleft and pouches are
opposed to each other forms-
Pharyngeal membrane

6. Structures formed in mesoderm of each arch
1. Skeletal element: Is cartilaginous, may remain
crtilaginous, may develop into bone or may
disappear
2. Striated Muscle: is supplied by nerve of the arch.
• Later muscle may or may not retain its
attachment to skeletal element of the arch.
• Muscle may subdivide to form number of distinct
muscles that may migrate away form pharyngeal
region but still carry their nerve with them.

7. Structures formed in mesoderm of each arch
3. Arteries of Pharyngeal Arches: Each pharyngeal
arch has its own artery that connects aortic sac
with the dorsal aorta.

8. Nerves of the Pharyngeal Arches:
Each arch is supplied by a nerve that Supplies-Skeletal Muscles
Its sensory branch supplies- overlying ectoderm &
endoderm(skin and mucous membrane).
•Morphologically each pharyngeal arch is supplied by 2 nerves.
Nerve that runs along cranial border of the arch- post-trematic
Nerve that runs along its caudal border is - pretrematic nerve.
In human beings, pretrematic nerves disappear from all arches
except first arch where it persists as chorda tympani nerve.

10. Derivatives of skeletal elements:
Meckel’s cartilage: cartilage of 1st arch
• From dorsal end- Incus & malleus
•Ventral part- is surrounded by
developing mandible & is absorbed.
•Part extending from region of middle
ear to mandible disappears but its
perichondrium forms:
 anteriror ligament of malleus &
 sphenomandibular ligament.
Mesenchyme of the first arch is
responsible for formation of bones of
face including mandible, maxilla,
zygomatic , palatine & part of temporal
bone

11. Mandibulofacial dysostosis, Treacher collins
syndrome or first arch syndrome:
Entire first arch may remain underdeveloped on one
or both sides, affecting maxilla, mandible external
ear & lower eyelid ( coloboma type defect) , palate
• prominence of cheek is absent,
• ear may be displaced ventrally and caudally,
•presence of cleft palate, faulty dentition

12. Reichert’s cartilage : Cartilage of 2nd arch
Derivatives
• Stapes
•Styloid process
•Stylohyoid ligament
•Smaller ( lesser) cornu of hyoid bone
•Superior (upper) part of body of hyoid
bone
Cartilage of the third arch:
Derivatives
•Greater cournu of hyoid bone
•Lower part of body of hyoid bone

13. Cartilage of fourth & sixth arch:
Derivatives
cartilage of larynx viz., thyroid,
cricoid, arytenoid, corniculate, and cuneiform
except epiglottis, which develops from caudal part
of hypobranchial eminence

14. Muscles derived from pharyngeal arch
1st arch: Muscles of mastication
(temporalis, masseter, medial &lateral
pterygoids), mylohyoid, anterior belly of
digastric, tensor veli palatini & tensor
tympani
2nd arch: Muscles of facial expression
(buccinator, occipitofrontalis, platysma,
orbicularis oris, orbicularis oculi),
posterior belly of digastric
stylohyoid, stapedius & Auricular muscles
3rd arch: stylopharyngeus
4th & 6th arch: Muscle of larynx & pharynx
(Cricothyroid, levator palati,constrictors of
pharynx, and intrinsic muscles of the larynx)

15. Nerve of the arch & muscle supplied by them:
Arch Nerve of Arch Muscle of Arch
First arch mandibular
nerve
Muscles of mastication
(temporalis, masseter, medial
and lateral pterygoids), mylohyoid, anterior
belly of
digastric, tensor veli palatini,
and tensor tympani
Second arch Facial Muscles of facial expression
(buccinator,occipitofrontalis,
platysma,orbicularis oris, orbicularis oculi),
posterior belly of digastric
stylohyoid, stapedius & Auricular muscles
Third arch Glossophryngeal stylopharyngeus
Fourth and
sixth arches
Superior laryngeal
Recurrent laryngeal
Muscle of larynx & pharynx
(Cricothyroid, levator palati,
constrictors of pharynx, and
intrinsic muscles of the larynx)

16. Fate of endodermal pouches:
First pharyngeal pouch: elongates to form a
diverticulum called tubotympanic recess.
Distal part- of tubotympanic recess expands-
forms middle ear cavity & mastoid antrum.
proximal part- remains tubular-forms
pharyngotympanic/ (eustachian / auditory) tube,-
communication between nasopharynx and
tympanic cavity (middle ear).

17. Fate of endodermal pouches:
Second pharyngeal pouch: Epithelium of ventral
part of this pouch contribute to forms tonsil.
(Dorsal part take part in formation of tubotymanic
recess.)
Third pharyngeal pouch: give rise to inferior
parathyroid & thymus
Fourth pharngeal pouch: gives rise to superior
parathyroid gland & may contribute to thyroid
gland
Fifth or ultimobranchial pouch: gets incorporated
with fourth pouch, & forms caudal pharyngeal
complex.
Superior parathyroid gland & parafollicular cells
of thyroid arise from complex.

18. Pharyngeal Clefts (Grooves)
There are four pharyngeal clefts or grooves
First pharyngeal cleft gives rise to -epithelial lining
of external auditory meatus.
Pinna / auricle is formed by series of swellings
( hillocks) that arise on first & second arch
whereas
2, 3 & 4th cleft are obliterated.

19. Pharyngeal Clefts (Grooves)
Second arch grows faster than succeding arch &
comes to overhang them.
Space between overhanging second arch & the
third arch, fourth arch & sixth arch is called cervical
sinus.
Cavity of cervical sinus is lined by ectoderm-
normally gets oblitereted

20. Part of cervical sinus may persist & give rise to
swelling that lie in the neck along anterior border of
sternocleidomastoid – called branchial cyst .
When branchial cyst ruptures a branchial fistula is
formed- found on lateral aspect of neck along the
anterior border of sternocleidomastoid.

21. THANK YOU