1. Pharyngeal arches
DR N SATYANARAYANA,FOM,DEPARTMENT OF ANATOMY.AIMST UNIVERSITY,MALAYSIA.

2. Pharyngeal arches
Cranial most part of foregut is called primitive pharynx
Primitive pharynx lies just caudal to stomodeum
Primitive pharynx is initially separated from the stomodeum by buccopharyngeal membrane
Endoderm of primitive pharynx is separated from the surface ectoderm by thin layer of mesoderm
Series of mesodermal thickenings appear on the lateral wall of primitive pharynx
These mesodermal thickenings are called pharyngeal (branchial) arches

3. Pharyngeal arches are 6 on each lateral wall of primitive pharynx
Each arch contains central core of mesoderm which is derived from paraxial and lateral plate mesoderm
Each arch is covered on the outer surface by the ectoderm and lined on the inner side by the endoderm
Pharyngeal arches separated externally from each other by pharyngeal grooves (clefts)
Pharyngeal arches separated internally from each other by pharyngeal pouches
5th pharyngeal arch soon degenerates after its formation

4. Pharyngeal arches

5. Pharyngeal pouch

6. 1. Pharyngeal arches 2. Lens placode 3. Pericardial swelling 4
1. Pharyngeal arches 2. Lens placode 3. Pericardial swelling 4. Pharyngeal clefts 5. Hand bud

7. Each arch contains Mesoderm: Cartilage (skeletal element):
which develops into muscles
Cartilage (skeletal element):
which develops into bones
Nerve: supplies
muscles developing from the mesoderm of the arch
skin developing from the ectoderm of the arch
mucous membrane developing from the endoderm of the arch
Aortic arch artery:
develop into arteries

8. First pharyngeal arch

10. First pharyngeal arch
First pharyngeal arch is called the mandibular arch
First arch gives 2 process – mandibular process and maxillary process
Structures derived from the first arch:
Structures developing from the cartilage of 1st arch (Meckel’s cartilage):
Incus and malleus bones of middle ear
Sphenomandibular ligament and anterior ligament of malleus

11. Structures developing from the mesoderm of 1st arch:
Muscles of mastication (masseter, temporalis, medial and lateral pterygoids)
Tensor tympani, tensor palati, mylohyoid and anterior belly of digastric
Maxilla, mandible, zygomatic bone, palatine bone, part of temporal bone
Nerve of the arch:
Mandibular nerve is the pretrematic nerve of 1st arch
Chorda tympani branch of facial nerve is post trematic nerve of 1st arch
1st aortic arch artery:
Forms part of maxillary artery

12. Second pharyngeal arch

13. Second pharyngeal arch
2nd pharyngeal arch is called hyoid arch
Structures derived from the 2nd arch:
Structures developing from the cartilage of 2nd arch (Reichert’s cartilage):
Stapes bone of middle ear
Styloid process, stylohyoid ligament
Lesser cornu and upper part of body of hyoid bone

14. Structures developing from the mesoderm of 2nd arch:
Muscles of face
Muscles of auricle (auricularis anterior, auricularis superior and auricularis posterior)
Muscles of scalp (occipito-frontalis)
Platysma, stapedius, posterior belly of digastric and stylohyoid
Nerve of the arch:
Facial nerve is the nerve of 2nd arch
2nd aortic arch artery:
Forms hyoid artery and stapedial artery which degenerates in the adults

15. Third pharyngeal arch

16. Third pharyngeal arch Structures derived from the third arch:
Structures developing from the cartilage of 3rd arch:
Greater cornu of hyoid bone
Lower part of body of hyoid bone
Structures developing from the mesoderm of 3rd arch:
Stylopharyngeus muscle
Nerve of the arch:
Glossopharyngeal nerve is the nerve of 3rd arch
3rd aortic arch artery:
Forms common carotid artery and part of internal carotid artery

17. Fourth and sixth pharyngeal arches

18. Fourth and sixth pharyngeal arches
Structures derived from the fourth and sixth arches:
Structures developing from the cartilage of 4th and 6th arches:
Cartilages of larynx – thyroid, cricoid, arytenoid, epiglottic, cuneiform and corniculate cartilages
Structures developing from the mesoderm of 4th arch:
Muscles of pharynx, soft palate and cricothyroid
Structures developing from the mesoderm of 6th arch:
Intrinsic muscles of larynx except cricothyroid

19. Nerve of the 4th arch: superior laryngeal nerve
Nerve of the 6th arch: recurrent laryngeal nerve
4th aortic arch artery:
Of the right side forms right subclavian artery
Of the left side forms arch of aorta
6th aortic arch artery:
On the right side forms right pulmonary artery
On the left side forms left pulmonary artery and ductus arteriosus

20. pharyngeal arch derivatives

21. Pharyngeal pouches

22. Pharyngeal pouches

23. Pharyngeal pouches
Pharyngeal arches are separated internally from each other by pharyngeal pouches
Pharyngeal pouches are lined by endoderm
Pharyngeal pouches are 5 in number
5th pharyngeal pouch is rudimentary and considered as part of 4th pouch
Endoderm lining the pouch develops into many structures

24. Fate of pharyngeal pouches
First pharyngeal pouch:
Dorsal part of 1st pouch along with dorsal part of 2nd pouch forms a stalk like diverticulum called tubotympanic recess
Tubotympanic recess comes in contact with first pharyngeal cleft
Distal part of tubotympanic recess becomes wide and forms middle ear cavity
Proximal part of tubotympanic recess remains narrow and forms auditory tube
Tympanic membranic is formed where tubotympanic recess touches the 1st pharyngeal cleft
1. External auditory meatus 2. Auditory tube 3. Primary tympanic cavity 4. Cervical sinus 5. Inferior parathyroid gland 6. Thymus 7. Palatine tonsil 8. Superior parathyroid gland 9. Ultimobranchial body

25. Second pharyngeal pouch:
Dorsal part takes part in the formation of tubotympanic recess along with dorsal part of 1st pouch
Endoderm of ventral part forms palatine tonsil
Third pharyngeal pouch:
Develops into thymus and inferior parathyroid gland
Fourth pharyngeal pouch:
Forms superior parathyroid gland
Forms parafollicular cells thyroid gland along the rudimentary 5th pouch
Fifth pharyngeal pouch:
Is rudimentary
Along with the part of 4th pouch it forms ultimobranchial body which gives origin to parafollicular cells of thyroid gland
1. External auditory meatus 2. Auditory tube 3. Primary tympanic cavity 4. Cervical sinus 5. Inferior parathyroid gland 6. Thymus 7. Palatine tonsil 8. Superior parathyroid gland 9. Ultimobranchial body

26. Fate of pharyngeal clefts

27. Fate of pharyngeal clefts
Pharyngeal arches are separated externally by pharyngeal clefts or grooves
Pharyngeal clefts are lined by ectoderm
First pharyngeal cleft:
Its dorsal part forms external acoustic meatus
Series of swellings (auricular hillocks) appear on the 1st and 2nd pharyngeal arch around the dorsal part of 1st cleft
These swellings join to form auricle or pinna of the ear
Other clefts:
Projection arising from the 2nd pharyngeal arch grows down over the lower pharyngeal arches

28. The space called cervical sinus separates this projection from the 3rd, 4th and 6th arches
This projection will fuse with the tissues lying caudal to the arches
The other arches and clefts become buried by the downward projection of 2nd arch, and side of neck becomes smooth
The cavity of cervical sinus normally disappears, sometimes part of it may persist and give rise to swelling in the neck called branchial cysts
If such a cyst opens on the surface on the neck, then its called branchial sinus

29. Structures developing the in the floor of primitive pharynx
Floor of primitive pharynx at the first pharyngeal arch shows 3 enlargements
Median swelling called tuberculum impar
2 lateral lingual sweelings
These swellings fuse to form anterior two-third of tongue
Just caudal to tuberculum impar floor of primitive pharynx shows thickening in the midline
This thickening forms thyroglossal duct which form thyroid gland
Floor of primitive pharynx at the region of 3rd and 4th pharyngeal arches shows a bulging called hypobranchial eminence (copula)

30. Tongue Development
These 3 drawings are viewed from inside the pharynx looking at the floor of the pharynx.
Mesodermal swellings in pharynx floor are covered with endoderm.
Foramen caecum is the site of initial thyroid cell descent into the hypopharyngeal eminence.

31. In the midline on the surface is a depression called the median sulcus.
Lateral lingual swellings have fused and overgrown medial and 2nd arch components.

32. Oral part is anterior 2/3
Pharyngeal part is posterior 1/3
Circumvillate papilla lie just anterior to terminal sulcus.
(Modified from Kaufman and Bard, 1999)

34. Floor of primitive pharynx

35. This hypobranchial eminence is divided in to cranial and caudal parts
Cranial part of hyphobranchial eminence grows cranially over the 2nd arch, joins lateral lingual swellings and tuberculum impar and forms posterior one-third of tongue
Caudal part of hypobranchial eminence forms epiglottis
Tracheobronchial groove appears in the floor of primitive pharynx caudal to hypobranchial eminence
This grows downs, elongates to form respiratory diverticulum
Respiratory diverticulum forms parts of the respiratory system like larynx, trachea, bronchial tree and lungs

36. Pharyngeal pouches
1. External auditory meatus 2. Auditory tube 3. Primary tympanic cavity 4. Cervical sinus 5. Inferior parathyroid gland 6. Thymus 7. Palatine tonsil 8. Superior parathyroid gland 9. Ultimobranchial body

37. Pharyngeal pouches
1. Auditory tube 2. Foramen cecum 3. Palatine tonsil 4. Ventral syde of pharynx 5. Tympanic cavity 6. Thyroid gland 7. Ultimobranchial body 8. Foregut 9. Thymus 10. Inferior parathyroid gland 11. Superior parathyroid gland 12. External auditory meatus