visceral arches

EVOLUTION OF VISCERAL ARCHES INTRODUCTION Visceral arches are pieces of cartilage or bone that support the pharyngeal region of vertebrates and also help to attach the jaws with the skull. There are typically 7 pairs of visceral arches in vertebrates which modified in different groups depending upon the presence of gills and type of jaw suspension. Visceral arches are numbered 1-7,the first arch is known as mandibular arch having two cartilaginous pieces called pterygoquadrate and mackel’s cartilage. Second visceral arch ,called hyoid arch,consists of hymandibular,ceratohyl and basihyl From 3 rd to 7 th visceral arches are called branchial arches , Since they support gills and typically consists of 4 pieces of cartilages,namely,pharyngobranchial,epibranchial,certobranchial,and hypobranchial. Cyclostomes There is no resemblance with typical pattern but cyclostomes possess a splanchocranium in which usual cartilages are not identifiable.thge whole pharyngeal skelton fuses to form a branchial basket to support gills. Elasmobranchs They contain full set of visceral arches and three unpaired branchial cartilages called basibranchials.the arrangement is close to basic pattern as they have 5 pairs of functional gills and skeleton is all cartilaginous Bony fishes Mackel’s cartilage forms articular and becomes part of the lower jaw,hyoid arch is modified for the movement of operculum and functioning of the lower jaw.Symplectic helps jaw suspension .last branchial arch shows sign of degeneration as the number of gills is reduced to 4 pairs Amphibian Latrval frogs have 6 visceral arches and last 3 bear gills .in urodeles having gills third,fourth and fifth epibranchial support gills while their basibranchials and ceratobranchial are reduced to two pairs ,hyomandibular modifies as columella of the middle ear cavity in frogs and toads. The air breathing hyobranchial apparatus of frog and toads is made by the fusion of 2 nd ,3 rd and 4 th visceral arches. ASIF IBRAHIM M.Sc, M-Phil,B.Ed, D-Pharma [email protected] [email protected] Mob. 9070262786

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EVOLUTIONOFVISCERALARCHES

INTRODUCTIONVisceral arches are pieces of cartilage or bone that support thepharyngealregionofvertebratesandalsohelptoattachthejawswiththeskull.Therearetypically7pairsofvisceralarchesinvertebrateswhichmodifiedindifferentgroupsdependinguponthepresenceofgillsandtypeofjawsuspension.Visceralarchesarenumbered1-7,thefirstarchisknownasmandibulararchhavingtwocartilaginouspiecescalledpterygoquadrateandmackel’scartilage.Second visceral arch ,called hyoid arch,consists of hymandibular,ceratohylandbasihylFrom3rdto7thvisceralarchesarecalledbranchialarches,

Since they support gills and typically consists of 4 pieces ofcartilages,namely,pharyngobranchial,epibranchial,certobranchial,andhypobranchial.

Cyclostomes

There is no resemblance with typical pattern but cyclostomes possess asplanchocranium in which usual cartilages are not identifiable.thge wholepharyngealskeltonfusestoformabranchialbaskettosupportgills.

ElasmobranchsTheycontainfullsetofvisceralarchesandthreeunpairedbranchialcartilagescalledbasibranchials.thearrangement isclosetobasicpatternastheyhave5pairsoffunctionalgillsandskeletonisallcartilaginous

BonyfishesMackel’s cartilage forms articular and becomes part of the lower jaw,hyoidarchismodifiedforthemovementofoperculumandfunctioningofthelowerjaw.Symplectic helps jaw suspension .last branchial arch shows sign ofdegenerationasthenumberofgillsisreducedto4pairs

AmphibianLatrvalfrogshave6visceralarchesandlast3beargills.inurodeleshavinggillsthird,fourth and fifth epibranchial support gillswhile their basibranchials andceratobranchialarereducedtotwopairs,hyomandibularmodifiesascolumellaof the middle ear cavity in frogs and toads. The air breathing hyobranchialapparatus of frog and toads ismadeby the fusionof 2nd ,3rd and 4th visceralarches.

ASIFIBRAHIMM.Sc,M-Phil,B.Ed,D-Pharma

[email protected]@gmail.com

Mob.9070262786

Reptiles

Quadrate and epipterygoid bones of the skull are modifications ofpterygoquadrate ,and articular of the lower jaw is a modified mackel’scartilage.Hyoid arch forms a small hyoid plate that also extends forwardsupportthetongue.oneoftwoceratobranchialsmayformtheposteriorcornuofthehypoidplate

BirdsModificationissimilartoreptilesexceptthatthereisonlyonecornuofhyoid

plateismodifiedfromthethirdvisceralarche.Mammals

Pterygoquadratebreaksintoalisphenoidandincus,theformerbecomespartof skull and latter joins the ear ossicles . Mackel’s cartilage modifies intomalleus and hyomandibular into stapes of the middle ear cavity .Larynx ofmammalsevolvedfromtheforthandfifthvisceralarches.Thyroidcartilageisamodificationof4thand5thvisceralarcheswhilearytenoidandcricoidcartilagesaremodifiedfifthvisceralarch

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Visceral Skeleton Start of Muscular. Visceral Skeleton Spanchnocranium –Develops within the pharyngeal arches –Fishes – jaw skeleton Gill arches