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Pharyngeal (Brachial) Apparatus

Pharyngeal apparatus includes the structures which form the neck and some structures of head region. Pharyngeal apparatus consists of:-
  1. Pharyngeal (brachial) arches, a series of mesodermal thickening lined on outside by ectoderm and on inside by endoderm, which appear in the wall of cranial most part of developing foregut. Initially there are six arches, but soon fifth arch disappears and only five are left.
  2. Pharyngeal pouches (endodermal pouches) refer to the outward bulging of endoderm (i.e. bulging of endoderm from inside out). This separates two pharyngeal arches internally.
  3. Pharyngeal clefts or grooves (ectodermal clefts) refer to inward dipping of ectoderm between two arches. Pharyngeal clefts lie opposite to pharyngeal pouches and thus in this area the ectoderm and endoderm lie close to each other without any intervening mesoderm.
  4. Pharyngeal membrane is thus formed where the ectoderm of pharyngeal clefts contacts the endoderm of pharyngeal pouches. Only one membrane (first pharyngeal membrane) contributes formation of adult structures. First pharyngeal membrane (along with intervening mesenchyme) becomes tympanic membrane.
Thus each pharyngeal arch has three parts: (i) ectodermal cleft (pharyngeal cleft) from ectoderm, (ii) mesodermal element (mesenchyme), and (iii) endodermal pouch (pharyngeal pouch) from endoderm. Hence structures derived from pharyngeal arches can be divided into:-
  1. Ectodermal derivatives: From ectodermal cleft.
  2. Endodermal derivatives: From endodermal pouch.
  3. Mesodermal derivatives: From mesenchyme.
The mesenchyme of each pharyngeal arch forms following components:
  1. skeletal component,
  2. muscular components,
  3. arterial component and
  4. Nerve supply.

Ectodermal and endodermal derivatives of pharyngeal arches

Arch Ectodermal cleft Endodermal pouch
I Epithelium of external auditory meatus, ear drum, Pinna
  • Ventral - tongue
  • Dorsal - tubotympanic recess ---- proximal part forms the auditory tube and the distal part forms the middle ear cavity and tympanic antrum
II 2nd arch grows over and
  • Palatine tonsil (lining epithelium)
III Covers the 2nd, 3rd and 4th clefts
  • Thymus
  • Inferior parathyroids
  • Superior parathyroids
  • Ultimo branchial body which form parafollicular C cells of thyroid
(Parafollicular cells are actually from neural crest cells)

Mesodermal derivatives of the pharyngeal arches

Arch Nerve of arch Skeletal element Muscles of arch
I Mandibular division of trigeminal Maxilla, zygomatic bone, part of temporal and vomer, sphenoid, mandible Meckel's cartilage -Malleus, incus Anterior ligament of malleus, sphenomandibular ligaments Mylohyoid, Mastication muscles, Anterior belly of digastric, Tensor veli palatine Tensor tympani
II Facial Reichert's cartilage, stapes (except footplate) Styloid process Stylohyoid ligament Smaller cornu of hyoid Superior part of body of hyoid Stapedius Stylohyoid Posterior belly of digastric, Facial expression muscles
III Glossopharyngeal Greater cornu of hyoid Lower part of body of hyoid Stylopharyngeus
IV Superior laryngeal branch of vagus Cartilage of larynx except arytenoids Pharyngeal muscles Cricothyroid
VI Recurrent laryngeal nerve Arytenoid cartilages of larynx Intrinsic muscles of larynx
(except cricothyroid)

Artery/Arteries of Arches

  1. Maxillary artery, external carotid artery
  2. Stapedial artery
  3. Carotid (common carotid/internal carotid)
  4. Left-arch of Aorta
    Right-subclavian artery (proximal part)
  5. Left-Left pulmonary artery, ductus arteriosus
    Right-Right pulmonary artery
Important points:
  1. First pharyngeal arch (mandibular arch) develops two prominences: smaller maxillary prominence (forms maxilla, zygomatic bone, squamous temporal bone) and larger mandibular prominence (forms mandible).
  2. Tympanic membrane derived from first pharyngeal membrane (which separates 1st pharyngeal groove from 1st pharyngeal pouch) represents all three layers of embryonic disc. It develops from three sources.
    1. External very thin skin is derived from ectoderm of 1st pharyngeal groove.
    2. Mesoderm of 1st and 2nd pharyngeal arches.
    3. Internal lining is derived from endoderm of tubotympanic recess (a derivative of 1st pharyngeal pouch).
  3. Tongue muscles originate from myoblast of occipital somites (occipital myotomes).
  4. Anterior 2/3 of tongue develops from 1st arch (lingual swelling) and tuberculum impar. Posterior 1/3 is developed from 3rd arch (cranial part of hypobronchial eminence). Posterior most part develops from 4th arch (dorsal part of hypo bronchial eminence).

Development of face

  1. Facial development occurs mainly between 4th and 8th weeks, and is induced by migration of cells of neural crest. Five facial primordia appear as prominences of mesenchyme: a frontonasal process, a pair of maxillary processes and a pair of mandibular processes.
  2. Frontonasal process is divided into:-
    1. Lateral nasal processes: From alae of nose.
    2. Medial nasal processes: These merge with each other to form intermaxillarysegment which gives rise to:
      1. philtrum (middle part of upper lip),
      2. Premaxillary plate.


Formation of various facial structures
Develops from
Upper lip
Philtrum (middle part): From intermaxillary segment (fused medial nasal processes) of frontonasal process.
Lateral parts: From maxillary processes.
Lower lip
From mandibular processes.
Upper jaw
From maxillary processes except for premaxilla (carries four incisors) which develop from intermaxillary segment offrontonasal process.
Lower jaw
From mandibular processes.
By fusion of maxillary process with mandibular process on each side.
Nasolacrimal duct
Canalization of ectodermal ridge formed by fusion oflateral nasal process with maxillary process.
Eye ball and orbit
Optic vesicle and surface ectoderm and mesoderm on either side of frontonasal process.


Congenital anomalies of lips
  1. Central cleft lip (upper): Due to failure of fusion of two medial nasal processes (intermaxillary segment).
  2. Lateral cleft lip (upper): Due to failure of fusion of medial nasal process with maxillary process.
  3. Central cleft lip (lower): Due to failure of fusion of mandibular processes with each other.

Development of palate

  1. Definitive palate develops from (i) Primitive palate and (ii) secondary plate.
    1. Primitive (primary) palate is derived from intermaxillary segment (formed by fusion of medial nasal processes of frontonasal process). It also forms premaxilla part of upper jaw (maxilla).
    2. Secondary palate is derived from fusion of Iateral palatine processes derived from maxillary process.
  2. Definitive palate is formed by fusion of secondary palate with primitive palate ventrally in Y-shaped manner. This junction is represented by incisive foramen. Definitive palate has two parts:
    1. Hard palate: Ventral (anterior) 3/4th part of definitive palate is ossified to form hard palate.
    2. Soft palate: Dorsal (posterior) 1/4th part of definitive palate remains unossfied and forms soft palate.
  3. Cleft palate occurs due to non-fusion of palatal process of maxillary process with each other or with frontonasal process.

Development of ear

Internal ear Middle ear External ear
It is the first part of the ear to develop Develops in 4th week and competes at 30th week
Tympanic membrane develops from all three germinallayers i.e.,
* Ectoderm of 1st pharyngeal cleft * Mesenchyme of 1st and 2nd pharyngeal arches * Endoderm of 1st pharyngeal pouch (tubotympanic recess)
Early in the 4th week (22 days), a thickening of surface ectoderm the otic pia codes appear which invaginate into underlying mesenchyme to form otic pit (27 days) and then otic or auditory vesicles (otocyst) - the primordium of membranous labyrinth (4.5 weeks). Tympanic cavity, eustachian tube, mastoid antrum and air cells develop from endoderm of first pharyngeal pouch.
External auditory meatus develops from dorsal portion of 1st pharyngeal groove (cleft)
* Meatal plug is formed at the beginning of 3rd month and dissolves in 7th month
Ventral saccular component of otic vesicle gives rise to saccule and cochlear duct, whereas dorsal utricular part forms small endolymphatic duct, utricle and semicircular canals. The lateral end of pouch expands and forms tubotympanic recess, which gives rise to primitive tympanic cavity whereas the proximal part forms auditory (eustachian) tube. Auricle (pinna) develops from 6 mesenchymal proliferations at the dorsal ends of 1st and 2nd pharyngeal arches
Development of membranous internal ear is completed by 16th weeks and reaches its adult size and shape by 20-22 weeks when the cochlea is developed sufficiently. Malleus and incus are derived from mesoderm (cartilage) of Ist pharyngeal arch and stapes from 2nd arch, except its foot plate and annular ligament which are derived from otic capsule.  

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