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Schematic of developing fetus with first, second and third arches labeled
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Floor of pharynx of human embryo about twenty-six days old
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Branchial+Arches
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A16254160
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In the
Development of
Vertebrate Animals , the (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
Gill s 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 .
- Contributes to the middle ear, Tonsils , supplied by the glossopharyngeal nerve.
- Derivatives include the superior parathyroid glands.
- 1
- McMinn, R., 1994. ''Last's anatomy: Regional and applied (9th ed).''
