Schematic of developing fetus with first, second and third arches labeled.
|- style="text-align: center;" class="hiddenStructure"
| colspan="2" |
|- style="text-align: center; line-height: 1;" class="hiddenStructure"
| colspan="2" |Floor of pharynx of human embryo about twenty-six days old.
|- class="hiddenStructure"
|Latin
|colspan="2"|
|- class="hiddenStructure"
|
|colspan="2"|[subject #13 ]
|- class="hiddenStructure"
|System
|colspan="2"|
|- class="hiddenStructure"
|Carnegie stage
|colspan="2"|[10]
|- class="hiddenStructure"
|Days
|colspan="2"|
|- class="hiddenStructure"
|Precursor
|colspan="2"|
|- class="hiddenStructure"
|Gives rise to
|colspan="2"|
|- class="hiddenStructure"
|MeSH
|colspan="2"|[A16.254.160]
|- class="hiddenStructure"
|Dorlands/Elsevier
|colspan="2"|[a_57/12149648]
|}
In the development of vertebrate animals, the branchial arches (or pharyngeal arches) develop during the fourth and fifth week in utero as a series of mesodermal outpouchings on the left and right sides of the developing pharynx. These grow and join in the ventral midline. The first arch, as the first to form, separates the mouth pit or stomodeum from the pericardium. By differential growth the neck elongates and new arches form, so the pharynx has six arches ultimately. Pharyngeal or branchial pouches form on the endodermal side between the arches, and pharyngeal grooves (or clefts) form from the lateral ectodermal surface of the neck region to separate the arches. The pouches line up with the clefts, and these thin segments become gills in fish. In mammals the endoderm and ectoderm not only remain intact, but continue to be separated by a mesoderm layer.
Each pharyngeal arch has a cartilaginous bar, a muscle component which differentiates from the cartilagenous tissue, an artery, and a cranial nerve.
There are six pharyngeal arches, but in humans the fifth arch only exists transiently during embryologic growth and development. Since no human structures result from the fifth arch, the arches in humans are I, II, III, IV, and VI. More is known about the fate of the first arch than the remaining four. The first three contribute to structures above the larynx, while the last three contribute to the larynx and trachea.
The first pharyngeal arch is also called the "mandibular arch". It is located between the stomodeum and the first pharyngeal groove. This arch gives rise to such things as the maxilla, mandible, the incus and malleus of the middle ear, and the muscles of mastication.
This is the only pouch in which the endoderm and ectoderm remain close together, as the tympanic membrane. There is minimal mesoderm in the tympanic membrane.
