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Embryology · Head and neck: pharyngeal arches

The pharyngeal apparatus: arches, pouches, clefts and membranes !

  • Embryonic structure

In week 4 the embryo's neck forms a row of bars with grooves between them. The face, ear, larynx and several glands come from them.

Updated 2026-11-01

See it in 3D: Pharynx · Mandible · Hyoid bone · Thyroid cartilage · Trigeminal nerve (V) · Facial nerve (VII) · Glossopharyngeal nerve (IX) · Vagus nerve

What it is

The pharyngeal apparatus is the set of arches, pouches, clefts and membranes that forms along the sides of the primitive pharynx in weeks 4 and 5. Each arch brings its own cranial nerve, muscles, skeleton and artery; each pouch gives glands and part of the middle ear. Almost all head and neck anatomy, and a large share of exam questions, can be traced back to it.

Key facts

  • Weeks 4–5: the arches appear in craniocaudal order and give the embryo its 'striped' neck.
  • There are five working arches: 1, 2, 3, 4 and 6. The fifth is rudimentary or never forms.
  • Outside, between the arches, lie the clefts (ectoderm); inside, the pouches (endoderm); between them, the membranes.
  • Humans never form gills: pouches and clefts do not open into each other.
  • Pouch endoderm patterns each arch, signalling to the mesenchyme (FGF8, BMP7, SHH).

Structure

  • Outer covering: surface ectoderm.
  • Inner lining: foregut (pharyngeal) endoderm.
  • Core: paraxial and lateral plate mesoderm (gives the muscles) and neural crest cells (give bone, cartilage and connective tissue).
  • Each arch carries four elements: a cranial nerve, a muscle component, a cartilage bar and an artery (an aortic arch).
  • Muscles keep the nerve of their arch even when they migrate far away: the nerve tells you the origin.

What it becomes

  • Arches: skeleton of the face and neck, ossicles, hyoid, laryngeal cartilages, and the muscles of chewing, facial expression, pharynx and larynx.
  • Pouches: tympanic cavity and auditory tube, palatine tonsil, thymus, parathyroids and thyroid C cells.
  • Clefts: only the first persists, as the external acoustic meatus; the others form the cervical sinus, which disappears.
  • Membranes: only the first persists, as the tympanic membrane.

Step by step

  1. Week 4: hindbrain neural crest migrates into the arches in three streams.
  2. Endodermal pouches push outward and clefts push inward, separating the arches.
  3. Each arch receives its aortic arch and its cranial nerve.
  4. Week 5: the second arch grows down over arches 3 and 4, closing off the cervical sinus.
  5. Weeks 5–7: the pouches give the thymus and parathyroid primordia, which migrate into the neck and chest.

Markers

  • Neural crest
  • HOX
  • OTX2
  • HOXA2
  • TBX1
  • FGF8
  • BMP7
  • SHH

Clinical notes

  • Neural crest failure causes craniofacial and cardiac outflow defects together (for example 22q11.2 deletion).
  • Leftover clefts or pouches give lateral neck cysts, sinuses and fistulas.
  • Alcohol and isotretinoin injure the neural crest and disturb first-arch derivatives.

Test yourself

Think of the answer, then tap the question to see it.

Which germ layer lines the pharyngeal pouches?

The endoderm of the primitive pharynx (foregut).

Which cells form the skeleton of the pharyngeal arches, and which form their muscles?

The skeleton comes from neural crest; the muscles come from paraxial mesoderm.

Which is the only pharyngeal cleft that persists in the adult, and what does it form?

The first: it forms the external acoustic meatus.

Which pharyngeal arch is rudimentary or absent in humans?

The fifth. The working arches are 1, 2, 3, 4 and 6.

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See it in 3D

The structures of Durgical's 3D anatomy where it is found.

← All of embryology

Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given.

Sources: Embryology, Branchial Arches - StatPearls - NCBI Bookshelf (StatPearls Publishing (NCBI Bookshelf), 2023); Embryology, Craniofacial Growth, And Development - StatPearls - NCBI Bookshelf (StatPearls Publishing (NCBI Bookshelf), 2023); Langman's Medical Embryology, 13th ed., ch. 17: Head and Neck (Wolters Kluwer, 2015).

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