Anatomy pharyngeal arch

• Pharyngeal arches


  Series of mesodermal thickenings that appear on the lateral wall of primitive pharynx
• Formation of pharyngeal arches

  1. Cranial most part of foregut is called primitive pharynx

  2. Primitive pharynx lies just caudal to stomodeum

  3. Primitive pharynx is initially separated from the stomodeum by buccopharyngeal membrane

  4. Endoderm of primitive pharynx is separated from the surface ectoderm by thin layer of mesoderm

  5. Series of mesodermal thickenings appear on the lateral wall of primitive pharynx

  6. These mesodermal thickenings are called pharyngeal (branchial) arches

  7. Pharyngeal arches are 6 on each lateral wall of primitive pharynx
• Pharyngeal arches


  • 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
• Contents of each pharyngeal arch

  • Mesoderm
  • Cartilage (skeletal element)
  • Nerve
  • Aortic arch artery
• Mesoderm in pharyngeal arches


  Develops into muscles and bones
• Cartilage in pharyngeal arches

  Develops into bones, cartilages and ligaments
• Nerves in pharyngeal arches


  Supplies muscles developing from the mesoderm of the arch, skin developing from the ectoderm of the arch, and mucous membrane developing from the endoderm of the arch
• Aortic arch arteries in pharyngeal arches

  Develop into arteries
• First pharyngeal arch (mandibular arch)

  • Gives 2 processes - mandibular process and maxillary process
  • Structures developing from the cartilage (Meckel's cartilage)
  • Structures developing from the mesoderm
  • Nerve (trigeminal nerve - mandibular and maxillary nerves)
  • Artery (1st aortic arch artery - forms part of maxillary artery)
• Second pharyngeal arch (hyoid arch)


  • Structures developing from the cartilage (Reichert's cartilage)
  • Structures developing from the mesoderm
  • Nerve (facial nerve)
  • Artery (2nd aortic arch artery - forms hyoid artery and stapedial artery which degenerates in the adults)
• Third pharyngeal arch


  • Structures developing from the cartilage
  • Structures developing from the mesoderm (stylopharyngeus muscle)
  • Nerve (glossopharyngeal nerve)
  • Artery (3rd aortic arch artery - forms common carotid artery and part of internal carotid artery)
• Fourth and sixth pharyngeal arches

  • Structures derived from the cartilage
  • Structures derived from the mesoderm
  • Nerve of the 4th arch (superior laryngeal nerve)
  • Nerve of the 6th arch (recurrent laryngeal nerve)
  • 4th aortic arch artery
  • 6th aortic arch artery
• 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
• Fate of first pharyngeal pouch

  1. First pouch forms a stalk like diverticulum called tubotympanic recess

  2. Tubotympanic recess comes in contact with first pharyngeal cleft

  3. Distal part of tubotympanic recess becomes wide and forms middle ear cavity

  4. Proximal part of tubotympanic recess remains narrow and forms auditory tube

  5. Tympanic membrane is formed where tubotympanic recess touches the 1st pharyngeal cleft
• Structures derived from pharyngeal pouches

  • External auditory meatus
  • Auditory tube
  • Primary tympanic (middle ear) cavity
  • Cervical sinus
  • Inferior parathyroid gland
  • Thymus
  • Palatine tonsil
  • Superior parathyroid gland
  • Ultimobranchial body

  
• Fate of pharyngeal clefts

  1. Pharyngeal arches are separated externally by pharyngeal clefts or grooves

  2. First pharyngeal cleft forms external acoustic meatus

  3. Series of swellings (auricular hillocks) appear on the 1st and 2nd pharyngeal arch around the 1st cleft, these join to form auricle or pinna of the ear

  4. Projection arising from the 2nd pharyngeal arch grows down over the lower pharyngeal arches, 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

  5. Other arches and clefts become buried by the downward projection of 2nd arch, and side of neck becomes smooth

  6. 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
• Development of structures in the floor of primitive pharynx

  1. Floor of primitive pharynx at the first pharyngeal arch shows 3 enlargements - median swelling called tuberculum impar and 2 lateral lingual sweelings, these swellings fuse to form anterior two-third of tongue

  2. Caudal to tuberculum impar, thyroglossal duct arises from the floor and forms thyroid gland

  3. Floor of primitive pharynx at the region of 3rd and 4th pharyngeal arches shows a bulging called hypobranchial eminence (copula)

  4. 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

  5. Caudal part of hypobranchial eminence forms epiglottis

  6. Tracheobronchial groove appears in the floor of primitive pharynx caudal to hypobranchial eminence, this grows downs, elongates to form respiratory diverticulum which forms parts of the respiratory system like larynx, trachea, bronchial tree and lungs

  
• Development of tongue


  • Anterior two-third (except vallate papilla) - Tuberculum impar and 2 lateral lingual swellings (1st arch endoderm)
  • Posterior one-third and vallate papilla - Cranial part of hypobranchial eminence (endoderm of third arch)
  • Muscles of tongue - Occipital myotomes