[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Embryology](https://durgical.com/en/embryology/) › [Head and neck: pharyngeal arches](https://durgical.com/en/embryology/#a-head_neck) › The pharyngeal apparatus: arches, pouches, clefts and membranes

[Embryology](https://durgical.com/en/embryology/) · [Head and neck: pharyngeal arches](https://durgical.com/en/embryology/#a-head_neck)

# 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](https://durgical.com/en/anatomy/pharynx/) · [Mandible](https://durgical.com/en/anatomy/mandible/) · [Hyoid bone](https://durgical.com/en/anatomy/hyoid-bone/) · [Thyroid cartilage](https://durgical.com/en/anatomy/thyroid-cartilage/) · [Trigeminal nerve (V)](https://durgical.com/en/anatomy/trigeminal-nerve/) · [Facial nerve (VII)](https://durgical.com/en/anatomy/facial-nerve/) · [Glossopharyngeal nerve (IX)](https://durgical.com/en/anatomy/glossopharyngeal-nerve/) · [Vagus nerve](https://durgical.com/en/anatomy/vagus-nerve/)

## Key points

- Arches = mesoderm + neural crest; pouches = endoderm; clefts = ectoderm.
- Working arches: 1, 2, 3, 4 and 6 (the 5th doesn't count).
- Each arch has its own nerve, muscle, cartilage and artery.
- Only the 1st cleft (external acoustic meatus) and 1st membrane (eardrum) persist.
- Neural crest builds the skeleton; mesoderm builds the muscles.

## 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

- Week 4: hindbrain neural crest migrates into the arches in three streams.
- Endodermal pouches push outward and clefts push inward, separating the arches.
- Each arch receives its aortic arch and its cranial nerve.
- Week 5: the second arch grows down over arches 3 and 4, closing off the cervical sinus.
- 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.

## Memory aid

Think of a sandwich: the outer slice is ectoderm (clefts), the inner slice is endoderm (pouches), and the filling (mesoderm and crest) is the arch.

## 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.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/embryology/the-pharyngeal-apparatus-arches-pouches-clefts-and-membranes/)

## See it in 3D

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

- [Pharynx](https://durgical.com/en/anatomy/pharynx/)
- [Mandible](https://durgical.com/en/anatomy/mandible/)
- [Hyoid bone](https://durgical.com/en/anatomy/hyoid-bone/)
- [Thyroid cartilage](https://durgical.com/en/anatomy/thyroid-cartilage/)
- [Trigeminal nerve (V)](https://durgical.com/en/anatomy/trigeminal-nerve/)
- [Facial nerve (VII)](https://durgical.com/en/anatomy/facial-nerve/)
- [Glossopharyngeal nerve (IX)](https://durgical.com/en/anatomy/glossopharyngeal-nerve/)
- [Vagus nerve](https://durgical.com/en/anatomy/vagus-nerve/)

## Related

- [Pharyngeal arches: nerve, muscles, skeleton and artery (the table)](https://durgical.com/en/embryology/pharyngeal-arches-nerve-muscles-skeleton-and-artery/)
- [First pharyngeal arch (mandibular arch) and the trigeminal nerve](https://durgical.com/en/embryology/first-pharyngeal-arch-and-the-trigeminal-nerve/)
- [Second pharyngeal arch (hyoid arch) and the facial nerve](https://durgical.com/en/embryology/second-pharyngeal-arch-and-the-facial-nerve/)
- [Third pharyngeal arch and the glossopharyngeal nerve](https://durgical.com/en/embryology/third-pharyngeal-arch-and-the-glossopharyngeal-nerve/)
- [Fourth and sixth pharyngeal arches: the larynx and the vagus nerve](https://durgical.com/en/embryology/fourth-and-sixth-pharyngeal-arches-the-larynx-and-the-vagus-nerve/)
- [Pharyngeal pouches: tonsil, thymus, parathyroids and C cells](https://durgical.com/en/embryology/pharyngeal-pouches-tonsil-thymus-parathyroids-and-c-cells/)
- [Pharyngeal clefts and membranes: external ear and cervical sinus](https://durgical.com/en/embryology/pharyngeal-clefts-and-membranes-external-ear-and-cervical-sinus/)
- [Neural crest cells and their derivatives](https://durgical.com/en/embryology/neural-crest-cells-and-their-derivatives/)
- [Aortic arch arteries and their derivatives](https://durgical.com/en/embryology/aortic-arch-arteries-and-their-derivatives/)
- [The face: five prominences](https://durgical.com/en/embryology/the-face-five-prominences/)
- [Foregut: esophagus, stomach rotation and duodenum](https://durgical.com/en/embryology/foregut-esophagus-stomach-rotation-and-duodenum/)

## Related conditions

- [DiGeorge syndrome (22q11.2 deletion syndrome)](https://durgical.com/en/conditions/digeorge-syndrome/)
- [Cleft lip and palate](https://durgical.com/en/conditions/cleft-lip-and-palate/)

[← All of embryology](https://durgical.com/en/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](https://www.ncbi.nlm.nih.gov/books/NBK538487/) (StatPearls Publishing (NCBI Bookshelf), 2023); [Embryology, Craniofacial Growth, And Development - StatPearls - NCBI Bookshelf](https://www.ncbi.nlm.nih.gov/books/NBK572156/) (StatPearls Publishing (NCBI Bookshelf), 2023); Langman's Medical Embryology, 13th ed., ch. 17: Head and Neck (Wolters Kluwer, 2015).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/embryology/the-pharyngeal-apparatus-arches-pouches-clefts-and-membranes/