Themouthis thebody orificethrough which manyanimalsingestfood andvocalize.Thebody cavityimmediately behind the mouth opening, known as theoral cavity(orcavum orisinLatin),[2]is also the first part of thealimentary canal,which leads to thepharynxand thegullet.Intetrapodvertebrates,the mouth is bounded on the outside by thelipsandcheeks— thus the oral cavity is also known as thebuccal cavity(from Latinbucca,meaning "cheek" )[3]— and contains thetongueon the inside. Except for some groups likebirdsandlissamphibians,vertebrates usually haveteethin their mouths,[4]although somefishspecies havepharyngeal teethinstead of oral teeth.
| Mouth | |
|---|---|
 | |
| Details | |
| Identifiers | |
| Latin | os, oris[1] |
| MeSH | D009055 |
| TA98 | A05.1.00.001 |
| TA2 | 119,2774 |
| FMA | 49184 |
| Anatomical terminology | |
Mostbilaterianphyla,includingarthropods,molluscsandchordates,have a two-openinggut tubewith a mouth at one end and ananusat the other. Which end forms first inontogenyis a criterion used to classify bilaterian animals intoprotostomesanddeuterostomes.
Development
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In the firstmulticellular animals,there was probably no mouth or gut and food particles were engulfed by the cells on the exterior surface by a process known asendocytosis.The particles became enclosed invacuolesinto which enzymes were secreted anddigestiontook placeintracellularly.The digestive products were absorbed into the cytoplasm and diffused into other cells. This form of digestion is used nowadays by simple organisms such asAmoebaandParameciumand also byspongeswhich, despite their large size, have no mouth or gut and capture their food by endocytosis.[5]
However,most animalshave a mouth and a gut, the lining of which is continuous with theepithelial cellson the surface of the body. A few animals which live parasitically originally had guts but have secondarily lost these structures. The original gut ofdiploblasticanimals probably consisted of a mouth and a one-way gut. Some modern invertebrates still have such a system: food being ingested through the mouth, partially broken down by enzymes secreted in the gut, and the resulting particles engulfed by the other cells in the gut lining. Indigestible waste is ejected through the mouth.[5]
In animals at least as complex as anearthworm,theembryoforms a dent on one side, theblastopore,which deepens to become thearchenteron,the first phase in the formation of thegut.In deuterostomes, the blastopore becomes the anus while the gut eventually tunnels through to make another opening, which forms the mouth. In the protostomes, it used to be thought that the blastopore formed the mouth (proto–meaning "first" ) while the anus formed later as an opening made by the other end of the gut. More recent research, however, shows that in protostomes the edges of the slit-like blastopore close up in the middle, leaving openings at both ends that become the mouth and anus.[6]
Anatomy
editInvertebrates
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Apart from sponges andplacozoans,almost all animals have an internal gut cavity, which is lined with gastrodermal cells. In less advanced invertebrates such as thesea anemone,the mouth also acts as an anus. Circular muscles around the mouth are able to relax or contract in order to open or close it. A fringe of tentacles thrusts food into the cavity and it can gape widely enough to accommodate large prey items. Food passes first into apharynxand digestion occurs extracellularly in thegastrovascular cavity.[7]Annelidshave simple tube-like guts, and the possession of an anus allows them to separate the digestion of their foodstuffs from the absorption of the nutrients.[8] Many molluscs have aradula,which is used to scrape microscopic particles off surfaces.[9]In invertebrates with hard exoskeletons, various mouthparts may be involved in feeding behaviour. Insects have a range of mouthparts suited to their mode of feeding. These include mandibles, maxillae and labium and can be modified into suitable appendages for chewing, cutting, piercing, sponging and sucking.[10]Decapodshave six pairs of mouth appendages, one pair of mandibles, two pairs of maxillae and three ofmaxillipeds.[11]Sea urchins have a set of five sharp calcareous plates, which are used as jaws and are known asAristotle's lantern.[12]
Vertebrates
editIn vertebrates, the first part of the digestive system is thebuccal cavity,commonly known as the mouth. The buccal cavity of a fish is separated from the opercular cavity by thegills.Water flows in through the mouth, passes over the gills and exits via theoperculumorgill slits.Nearly all fish havejawsand may seize food with them but most feed by opening their jaws, expanding their pharynx and sucking in food items. The food may be held or chewed by teeth located in the jaws, on the roof of the mouth, on the pharynx or on thegill arches.[13]
Nearly all amphibians are carnivorous as adults. Many catch their prey by flicking out an elongated tongue with a sticky tip and drawing it back into the mouth, where they hold the prey with their jaws. They then swallow their food whole without much chewing.[14]They typically have many small hingedpedicellate teeth,the bases of which are attached to the jaws, while the crowns break off at intervals and are replaced. Most amphibians have one or two rows of teeth in both jaws but some frogs lack teeth in the lower jaw. In many amphibians, there are alsovomerine teethattached to the bone in the roof of the mouth.[15]
The mouths of reptiles are largely similar to those of mammals. Thecrocodiliansare the only reptiles to have teeth anchored insocketsin their jaws.[16]They are able to replace each of their approximately 80 teeth up to 50 times during their lives.[17]Most reptiles are either carnivorous or insectivorous, but turtles are often herbivorous. Lacking teeth that are suitable for efficiently chewing of their food, turtles often havegastrolithsin their stomach to further grind the plant material.[18]Snakes have a very flexible lower jaw, the two halves of which are not rigidly attached, and numerous other joints in their skull. These modifications allow them to open their mouths wide enough to swallow their prey whole, even if it is wider than they are.[19]
Birds do not have teeth, relying instead on other means of gripping and macerating their food. Theirbeakshave a range of sizes and shapes according to their diet and are composed of elongated mandibles. The upper mandible may have a nasofrontal hinge allowing the beak to open wider than would otherwise be possible. The exterior surface of beaks is composed of a thin, horny sheath ofkeratin.[20]Nectar feeders such ashummingbirdshave specially adapted brushy tongues for sucking up nectar from flowers.[21]
In mammals, the buccal cavity is typically roofed by thehardandsoft palates,floored by thetongueand surrounded by thecheeks,salivary glands,and upper and lowerteeth.The upper teeth are embedded in theupper jawand the lower teeth in thelower jaw,which articulates with thetemporal bonesof theskull.Thelipsare soft and fleshy folds which shape the entrance into the mouth. The buccal cavity empties through thepharynxinto theoesophagus.[22]
Other functions of the mouth
editCrocodiliansliving in the tropics can gape with their mouths to provide cooling byevaporationfrom the mouth lining.[23]Some mammals rely on panting forthermoregulationas it increases evaporation of water across the moist surfaces of the lungs, the tongue and mouth. Birds also avoid overheating by gular fluttering, flapping the wings near the gular (throat) skin, similar to panting in mammals.[24]
Various animals use their mouths in threat displays. They may gape widely, exhibit their teeth prominently, or flash the startling colours of the mouth lining. This display allows each potential combatant an opportunity to assess the weapons of their opponent and lessens the likelihood of actual combat being necessary.[25]
A number of species of bird use agaping,open beak in their fear and threat displays. Some augment the display by hissing or breathing heavily, while others clap their beaks.[26]
Mouths are also used as part of the mechanism for producing sounds for communication. To produce sounds, air is forced from the lungs overvocal cordsin the larynx. In humans, the pharynx, soft palate, hard palate,alveolar ridge,tongue, teeth and lips are termedarticulatorsand play their part in the production ofspeech.Varying the position of the tongue in relation to the other articulators or moving the lips restricts the airflow from the lungs in different ways and changes the mouth's resonating properties, producing a range of different sounds.[27]In frogs, the sounds can be amplified using sacs in the throat region. The vocal sacs can be inflated and deflated and act as resonators to transfer the sound to the outside world.[28]A bird's song is produced by the flow of air over a vocal organ at the base of thetrachea,thesyrinx.For each burst of song, the bird opens its beak and closes it again afterwards. The beak may move slightly and may contribute to the resonance but the song originates elsewhere.[29]
See also
editReferences
edit- ^Schröder, Hannsjörg; Moser, Natasha; Huggenberger, Stefan (2020).Neuroanatomy of the Mouse: An Introduction.Springer International Publishing. p. 105.ISBN978-3-03019-898-5.RetrievedDecember 24,2023.
- ^Gray, Henry(1918)."2a. The Mouth".Gray's Anatomy.Archivedfrom the original on Oct 10, 2022.
- ^"Buccal definition".Dictionary Reference.The Free Dictionary.Retrieved18 July2013.
- ^"Mouth definition".Dictionary Reference.The Free Dictionary.Archivedfrom the original on Sep 30, 2013.Retrieved18 July2013.
- ^abDorit, R. L.; Walker, W. F.; Barnes, R. D. (1991).Zoology.Saunders College Publishing. pp.241–242.ISBN978-0-03-030504-7.
- ^Arendt, D.; Technau, U.; Wittbrodt, J. (2001). "Evolution of the bilaterian larval foregut".Nature.409(6816): 81–85.Bibcode:2001Natur.409...81A.doi:10.1038/35051075.PMID11343117.S2CID4406268.
- ^Ruppert, Edward E.; Fox, Richard, S.; Barnes, Robert D. (2004).Invertebrate Zoology, 7th edition.Cengage Learning. p. 103.ISBN978-81-315-0104-7.
{{cite book}}:CS1 maint: multiple names: authors list (link) - ^Ruppert, Edward E.; Fox, Richard, S.; Barnes, Robert D. (2004).Invertebrate Zoology, 7th edition.Cengage Learning. p. 428.ISBN978-81-315-0104-7.
{{cite book}}:CS1 maint: multiple names: authors list (link) - ^Ruppert, Edward E.; Fox, Richard, S.; Barnes, Robert D. (2004).Invertebrate Zoology, 7th edition.Cengage Learning. p. 286.ISBN978-81-315-0104-7.
{{cite book}}:CS1 maint: multiple names: authors list (link) - ^Ruppert, Edward E.; Fox, Richard, S.; Barnes, Robert D. (2004).Invertebrate Zoology, 7th edition.Cengage Learning. pp. 727–731.ISBN978-81-315-0104-7.
{{cite book}}:CS1 maint: multiple names: authors list (link) - ^Ruppert, Edward E.; Fox, Richard, S.; Barnes, Robert D. (2004).Invertebrate Zoology, 7th edition.Cengage Learning. p. 634.ISBN978-81-315-0104-7.
{{cite book}}:CS1 maint: multiple names: authors list (link) - ^Ruppert, Edward E.; Fox, Richard, S.; Barnes, Robert D. (2004).Invertebrate Zoology, 7th edition.Cengage Learning. p. 902.ISBN978-81-315-0104-7.
{{cite book}}:CS1 maint: multiple names: authors list (link) - ^Dorit, R. L.; Walker, W. F.; Barnes, R. D. (1991).Zoology.Saunders College Publishing. p.818.ISBN978-0-03-030504-7.
- ^Dorit, R. L.; Walker, W. F.; Barnes, R. D. (1991).Zoology.Saunders College Publishing. p.847.ISBN978-0-03-030504-7.
- ^Stebbins, Robert C.;Cohen, Nathan W. (1995).A Natural History of Amphibians.Princeton University Press. pp. 57–58.ISBN978-0-691-03281-8.
- ^LeBlanc, A. R. H.; Reisz, R. R. (2013). Viriot, Laurent (ed.)."Periodontal ligament, cementum, and alveolar bone in the oldest herbivorous tetrapods, and their evolutionary significance".PLOS ONE.8(9): e74697.Bibcode:2013PLoSO...874697L.doi:10.1371/journal.pone.0074697.PMC3762739.PMID24023957.
- ^Nuwer, Rachel(13 May 2013)."Solving an alligator mystery may help humans regrow lost teeth".Smithsonian.com.Archived fromthe originalon Jun 12, 2013.Retrieved4 November2013.
- ^King, Gillian (1996).Reptiles and Herbivory.Chapman & Hall.ISBN0412461102.
- ^Behler, John L.; King, F. Wayne (1979).The Audubon Society Field Guide to Reptiles and Amphibians of North America.Alfred A. Knopf. p.581.ISBN0-394-50824-6.
- ^Gill, Frank B. (1995).Ornithology(2 ed.). W. H. Freeman & Co. p. 149.ISBN0-7167-2415-4.
- ^Paton, D. C.; Collins, B. G. (1 April 1989). "Bills and tongues of nectar-feeding birds: A review of morphology, function, and performance, with intercontinental comparisons".Australian Journal of Ecology.14(4): 473–506.doi:10.1111/j.1442-9993.1989.tb01457.x.
- ^Pourtauborde, Aniza."What is the buccal cavity?".WiseGeek.Conjecture Corporation.Retrieved2013-11-30.
- ^Ross, Charles A., ed. (1992).Crocodiles and Alligators.Blitz. pp. 48–51.ISBN978-1-85391-092-0.
- ^Robertshaw, David (2006). "Mechanisms for the control of respiratory evaporative heat loss in panting animals".Journal of Applied Physiology.101(2): 664–668.doi:10.1152/japplphysiol.01380.2005.PMID16675613.
- ^"Showing Off Your Weapons In The Animal Kingdom: Threat Displays May Prevent Serious Physical Harm".ScienceDaily.2006-06-21.Retrieved2013-11-30.
- ^Rogers, Lesley J.;Kaplan, Gisela T.(2000).Songs, Roars and Rituals: Communication in Birds, Mammals and Other Animals.Boston, MA: Harvard University Press. p.79.ISBN0-674-00827-8.
- ^"The production of speech sounds: Articulators above the larynx".personal.rdg.ac.uk.Retrieved2013-11-30.
- ^Stebbins, Robert C.;Cohen, Nathan W. (1995).A Natural History of Amphibians.Princeton University Press. p. 77.ISBN978-0-691-03281-8.
- ^Ehrlich, Paul R.; Dobkin, David S.; Wheye, Darryl (1998)."Bird voices".web.stanford.edu.Retrieved2013-11-30.
