Skull 168859 225942981 2008-07-16T03:25:59Z 198.53.145.103 {{otherusesof|Skull}}{{redirect|Cranium}} [[Image:Skullclose.jpg|thumb|right|250px|A closeup of the front of a damaged human skull.]] The '''skull''' is a [[bone|bony]] structure found in the head of many [[animal]]s. The skull supports the structures of the [[face]] and protects the [[head]] against injury. The skull can be subdivided into two parts: the '''cranium''' and the '''mandible'''. A skull that is missing a mandible is only a cranium; this is the source of a very commonly made error in terminology. Those animals having skulls are called [[Craniata|craniates]]. Protection of the brain is only one part of the function of a bony skull. For example, a fixed distance between the eyes is essential for [[stereoscopic vision]], and a fixed position for the ears helps the brain to use auditory cues to judge direction and distance of sounds. In some animals, the skull also has a defensive function (e.g. horned [[ungulates]]); the [[frontal bone]] is where horns are mounted. ==Human skulls== {{main|Human skull}} [[Image:Human skull front simplified (bones).svg|thumb|220px|Human skull (front)]] [[Image:Human skull side simplified (bones).svg|thumb|222px|Human skull (side)]] In humans, the adult skull is normally made up of 22 [[bones]]. Except for the [[mandible]], all of the bones of the skull are joined together by [[sutures of skull|sutures]], rigid articulations permitting very little movement. Eight bones form the ''neurocranium'' (braincase)—including the frontal, parietals, [[occipital bone]], [[sphenoid]], temporals and [[ethmoid]]—a protective [[cranial vault|vault surrounding the brain]]. Fourteen bones form the ''splanchnocranium'', the bones supporting the face. Encased within the [[temporal bone]]s are the six ''ear [[ossicles]]'' of the [[middle ear]]s, though these are not part of the skull. The [[hyoid bone]], supporting the [[tongue]], is usually not considered as part of the skull either, as it does not articulate with any other bones.The skull is a protector of the brain. The skull contains the [[sinus cavity|sinus cavities]], which are air-filled cavities lined with [[respiratory epithelium]], which also lines the large airways. The exact functions of the sinuses are unclear; they may contribute to decreasing the weight of the skull with a minimal decrease in strength,or they may be important in improving the resonance of the voice. In some animals, such as the [[elephant]], the sinuses are extensive. The elephant skull needs to be very large, to form an attachment for muscles of the neck and trunk, but is also unexpectedly light; the comparatively small brain-case is surrounded by large sinuses which reduce the weight. The [[meninges]] are the three layers, or membranes, which surround the structures of the [[nervous system]]. They are known as the [[dura mater]], the [[arachnoid mater]] and the [[pia mater]]. Other than being classified together, they have little in common with each other. In humans, the [[anatomical position]] for the skull is the [[Frankfurt plane]], where the lower margins of the [[orbit (anatomy)|orbits]] and the upper borders of the [[ear canal]]s are all in a horizontal plane. This is the position where the subject is standing and looking directly forward. For comparison, the skulls of other species, notably [[primates]] and [[hominids]], may sometimes be studied in the Frankfurt plane. However, this does not always equate to a natural posture in life. ==Other skulls== ===Temporal Fenestra=== [[Image:Massospondylus Skull Steveoc 86.png|thumb|This ''[[Massospondylus]]'' skull shows the two temporal fenestrae typical of [[diapsid]]s.]] The temporal [[fenestra]] are anatomical features of the [[amniota|amniote]] skull, characterised by bilaterally symmetrical holes (fenestrae) in the temporal bone. Depending on the lineage of a given animal, two, one, or no pairs of temporal fenestrae may be present, above or below the [[postorbital]] and [[squamosal]] bones. The upper temporal fenestrae are also known as the supratemporal fenestrae, and the lower temporal fenestrae are also known as the infratemporal fenestrae. The presence and morphology of the temporal fenestra is critical for taxonomic classification of the synapsids, of which mammals are part. Physiological speculation associates it with a rise in metabolic rates and an increase in jaw musculature. The earlier amniotes of the Carboniferous did not have temporal fenestrae but the more advanced sauropsids and synapsids did. As time progressed, sauropsids' and synapsids' temporal fenestrae became more modified and larger to make stronger bites and more jaw muscles. Dinosaurs, which are sauropsids, have large advanced openings and their descendants, the birds, have temporal fenestrae which have been modified. Mammals, which are synapsids, possess no fenestral openings in the skull, as the trait has been modified. They do, though, still have the temporal orbit (which resembles an opening) and the temporal muscles. It is a hole in the head and is situated to the rear of the orbit behind the eye. ====Classification==== [[Image:Gray188.png|thumb|200px|Humans, despite having lost their [[fenestræ]], are [[synapsid]]s]] There are four types of amniote skull, classified by the number and location of their fenestra. These are: * [[Anapsid]]a - no openings * [[Synapsid]]a - one low opening (beneath the postorbital and squamosal bones) * [[Euryapsida]] - one high opening (above the postorbital and squamosal bones); euryapsids actually evolved from a diapsid configuration, losing their lower temporal fenestra. * [[Diapsid]]a - two openings Evolutionary, they are related as follows: *[[Amniota]] **Class '''[[Synapsid]]a''' ***Order [[Therapsida]] ****Class [[Mammal]]ia - mammals **Class [[Sauropsid]]a - reptiles ***Subclass '''[[Anapsid]]a''' ***(unranked) [[Eureptilia]] ****Subclass '''[[Diapsid]]a''' *****(unranked) '''[[Euryapsida]]''' *****Class [[bird|Aves]] - birds <gallery> Image:Hippo skull dark.jpg|A [[hippopotamus]]' skull Image:Tyrannoskull.jpg|A ''[[Tyrannosaurus]]'' skull Image:Felis catus-skull-drawing.jpg|A [[cat]] skull, a typical skull of a [[carnivore]] Image:Nutriaschädel.jpg|A [[coypu]] skull, a typical rodent Image:Bulldog-skull.JPG|A [[bulldog]] skull Image:George's skull1.jpg|A [[gerbil]] skull </gallery> == See also == *[[Craniometry]] *[[Bone#Terminology|Bone terminology]] *[[Anatomical terms of location]] *[[Head and neck anatomy]] *[[Phrenology]], the pseudoscientific process of determining personality from the shape of the head. *[[Skull (symbolism)]] ==References== *White, T.D. 1991. Human osteology. Academic Press, Inc. San Diego, CA. ==External links== {{commonscat|Skulls}} {{Wiktionary}} *[http://www.d91.k12.id.us/skyline/teachers/robertsd/skulls.htm Animal Skull Collection] (Over 300 animal skull images compiled by U.S. high-school teacher) *[http://www.a-life-with-skulls.com/index.html Ray Bandar: A Life With Skulls] Film about California animal skull collector Ray Bandar *[http://www.wtamu.edu/~rmatlack/Mammalogy/lab1.htm Skull terminology site by Texas A&M] *[http://www.welovelmc.com/books/anatomy/cranialcavity.htm Anatomy of cranial cavity.] *[http://www.csuchico.edu/anth/Module/skull.html Dept of Anth Skull Module] *[http://www.gwc.maricopa.edu/class/bio201/skull/skulltt.htm Skull Anatomy Tutorial.] *[http://www.gmanews.tv/video/16975/Baby-born-without-skull GMA NEWS.TV, video, (Filipino language) Baby born without skull - 01/19/2008] [[Category:Skull| ]] [[Category:Animal anatomy]] [[Category:Head and neck]] [[Category:Flat bones]] [[ar:جمجمة]] [[arc:ܩܪܩܦܬܐ]] [[bg:Череп]] [[ca:Crani]] [[cs:Lebka]] [[cy:Penglog]] [[da:Kranium]] [[de:Schädel]] [[dv:ބޮލުގެ ނާށިގަނޑު]] [[et:Kolju]] [[es:Cráneo]] [[eo:Kranio]] [[eu:Burezur]] [[fa:جمجمه]] [[fr:Crâne]] [[gl:Cranio]] [[ko:두개골]] [[hr:Lubanja]] [[id:Tengkorak]] [[os:Сæргæхц]] [[is:Höfuðkúpa]] [[it:Cranio]] [[he:גולגולת]] [[ku:Kilox]] [[la:Calva]] [[lv:Galvaskauss]] [[lt:Galvos griaučiai]] [[hu:Koponya]] [[nl:Schedel]] [[ja:頭蓋骨]] [[no:Skalle]] [[pag:Lapislapis]] [[pl:Czaszka]] [[pt:Crânio]] [[ro:Craniu]] [[qu:Uma tullu]] [[ru:Череп]] [[simple:Skull]] [[sk:Lebka]] [[sl:Lobanja]] [[sr:Лобања]] [[fi:Pääkallo]] [[sv:Kranium]] [[te:కపాలం]] [[th:กะโหลกศีรษะ]] [[uk:Череп]] [[zh:颅骨]]