AskDefine | Define skulls

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Noun

skulls
  1. Plural of skull

Extensive Definition

otherusesof Skull The skull is a bony structure found in the head of many animals. 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 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

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, rigid articulations permitting very little movement. Eight bones form the neurocranium (braincase)—including the frontal, parietals, occipital bone, sphenoid, temporals and ethmoid—a protective vault surrounding the brain. Fourteen bones form the splanchnocranium, the bones supporting the face. Encased within the temporal bones are the six ear ossicles of the middle ears, 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 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 orbits and the upper borders of the ear canals 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.

Possible types of skull fractures

Other skulls

Temporal Fenestra

The temporal fenestra are anatomical features of the 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

There are four types of amniote skull, classified by the number and location of their fenestra. These are:
  • Anapsida - no openings
  • Synapsida - 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.
  • Diapsida - two openings
Evolutionary, they are related as follows:

See also

References

  • White, T.D. 1991. Human osteology. Academic Press, Inc. San Diego, CA.
skulls in Arabic: جمجمة
skulls in Official Aramaic (700-300 BCE): ܩܪܩܦܬܐ
skulls in Bulgarian: Череп
skulls in Catalan: Crani
skulls in Czech: Lebka
skulls in Welsh: Penglog
skulls in Danish: Kranium
skulls in German: Schädel
skulls in Dhivehi: ބޮލުގެ ނާށިގަނޑު
skulls in Estonian: Kolju
skulls in Spanish: Cráneo
skulls in Esperanto: Kranio
skulls in Basque: Burezur
skulls in Persian: جمجمه
skulls in French: Crâne
skulls in Galician: Cranio
skulls in Korean: 두개골
skulls in Croatian: Lubanja
skulls in Indonesian: Tengkorak
skulls in Ossetian: Сæргæхц
skulls in Icelandic: Höfuðkúpa
skulls in Italian: Cranio
skulls in Hebrew: גולגולת
skulls in Kurdish: Kilox
skulls in Latin: Calva
skulls in Latvian: Galvaskauss
skulls in Lithuanian: Galvos griaučiai
skulls in Hungarian: Koponya
skulls in Dutch: Schedel
skulls in Japanese: 頭蓋骨
skulls in Norwegian: Skalle
skulls in Pangasinan: Lapislapis
skulls in Polish: Czaszka
skulls in Portuguese: Crânio
skulls in Romanian: Craniu
skulls in Quechua: Uma tullu
skulls in Russian: Череп
skulls in Simple English: Skull
skulls in Slovak: Lebka
skulls in Slovenian: Lobanja
skulls in Serbian: Лобања
skulls in Finnish: Pääkallo
skulls in Swedish: Kranium
skulls in Thai: กะโหลกศีรษะ
skulls in Ukrainian: Череп
skulls in Chinese: 颅骨
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