1.(MeSH)A region, of SOMITE development period, that contains a number of paired arches, each with a mesodermal core lined by ectoderm and endoderm on the two sides. In lower aquatic vertebrates, branchial arches develop into GILLS. In higher vertebrates, the arches forms outpouchings and develop into structures of the head and neck. Separating the arches are the branchial clefts or grooves.
definition of Wikipedia
Pharyngeal Arch (n.) [MeSH]
|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|
||This article needs additional citations for verification. (August 2010)|
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, 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.
Dictionary and translator for handheld
New : sensagent is now available on your handheld
A windows (pop-into) of information (full-content of Sensagent) triggered by double-clicking any word on your webpage. Give contextual explanation and translation from your sites !
With a SensagentBox, visitors to your site can access reliable information on over 5 million pages provided by Sensagent.com. Choose the design that fits your site.
Improve your site content
Add new content to your site from Sensagent by XML.
Crawl products or adds
Get XML access to reach the best products.
Index images and define metadata
Get XML access to fix the meaning of your metadata.
Please, email us to describe your idea.
Lettris is a curious tetris-clone game where all the bricks have the same square shape but different content. Each square carries a letter. To make squares disappear and save space for other squares you have to assemble English words (left, right, up, down) from the falling squares.
Boggle gives you 3 minutes to find as many words (3 letters or more) as you can in a grid of 16 letters. You can also try the grid of 16 letters. Letters must be adjacent and longer words score better. See if you can get into the grid Hall of Fame !
Change the target language to find translations.
Tips: browse the semantic fields (see From ideas to words) in two languages to learn more.