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|Schematic of developing fetus with first, second and third arches labeled.|
|Floor of pharynx of human embryo about twenty-six days old.|
|Gray's||subject #13 65|
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In the development of vertebrate animals, the pharyngeal arches (which develop into the branchial arches or gill arches in fish) are anlage for a multitude of structures. In humans, they develop during the fourth week in utero as a series of mesodermal outpouchings on the left and right sides of the developing pharynx. In fish, the branchial arches support the gills.
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.
Each pharyngeal arch has a cartilaginous stick, a muscle component which differentiates from the cartilaginous tissue, an artery, and a cranial nerve. Each of these is surrounded by mesenchyme. Arches do not develop simultaneously, but instead possess a "staggered" development.
Pharyngeal pouches (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.
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.
|Pharyngeal arch||Muscular contributions||Skeletal contributions||Nerve||Artery|
|1st (also called "mandibular arch")||Muscles of mastication, anterior belly of the digastric, mylohyoid, tensor tympani, tensor veli palatini||Maxilla, mandible (only as a model for mandible not actual formation of mandible), the incus and malleus of the middle ear, also Meckel's cartilage||Trigeminal nerve (V2 and V3)||Maxillary artery, external carotid artery|
|2nd (also called the "hyoid arch")||Muscles of facial expression, buccinator, platysma, stapedius, stylohyoid, posterior belly of the digastric||Stapes, temporal styloid process, hyoid (lesser horn and upper part of body), Reichert's cartilage||Facial nerve (VII)||Stapedial artery, hyoid artery|
|3rd||Stylopharyngeus||Hyoid (greater horn and lower part of body), thymus, inferior parathyroids||Glossopharyngeal nerve (IX)||Common carotid, internal carotid|
|4th||Cricothyroid muscle, all intrinsic muscles of soft palate including levator veli palatini||Thyroid cartilage, superior parathyroids, epiglottic cartilage||Vagus nerve (X), superior laryngeal nerve||Right 4th aortic arch: subclavian artery|
Left 4th aortic arch: aortic arch
|6th||All intrinsic muscles of larynx except the cricothyroid muscle||Cricoid cartilage, arytenoid cartilages, corniculate cartilage||Vagus nerve (X), recurrent laryngeal nerve||Right 6th aortic arch: pulmonary artery|
The development of the pharyngeal arches provide a useful morphological landmark with which to establish the precise stage of embryonic development. Their formation and development corresponds to Carnegie stages 10 to 16 in mammals, and Hamburger-Hamilton stages 14 to 28 in the chicken.