Editing Skull (section)

==Structure==
=== Humans{{anchor|Structure_of_human_skull}} ===
{{about||details and the constituent bones|Neurocranium|and|Facial skeleton}}
[[File:Lateral head skull.jpg|thumb|upright=.8|Skull in situ]]
[[File:Anatomy of the Human Bone 22.jpg|thumb|Human head skull from side]]
[[File:621 Anatomy of a Flat Bone.jpg|thumb|left|Anatomy of a flat bone – the periosteum of the neurocranium is known as the [[periosteum|pericranium]]]]
[[File:Sobo 1909 38.png|thumb|upright=.8|Human skull from the front]]
[[File:Human skull side simplified (bones).svg|thumb|upright=.8|Side bones of skull]]
The '''human skull''' is the bone structure that forms the [[human head|head]] in the [[human skeleton]]. It supports the structures of the [[face]] and forms a cavity for the [[Human brain|brain]]. Like the skulls of other vertebrates, it protects the brain from injury.<ref>{{Cite book|url=https://books.google.com/books?id=NiTLf7g1n04C|title=Anatomy Coloring Workbook|last=Alcamo|first=I. Edward|date=2003|publisher=The Princeton Review|isbn=9780375763427|pages=22–25|language=en}}</ref>

The skull consists of three parts, of different [[embryology|embryological]] origin—the [[neurocranium]], the [[Fibrous joint#Sutures|sutures]], and the [[facial skeleton]]. The neurocranium (or ''braincase'') forms the protective [[cranial cavity]] that surrounds and houses the brain and [[brainstem]].<ref>{{Cite book|url=https://books.google.com/books?id=M8WgDwAAQBAJ&pg=PA2|title=Comprehensive and Clinical Anatomy of the Middle Ear|last1=Mansour|first1=Salah|last2=Magnan|first2=Jacques|last3=Ahmad|first3=Hassan Haidar|last4=Nicolas|first4=Karen|last5=Louryan|first5=Stéphane|date=2019|publisher=Springer|isbn=9783030153632|pages=2|language=en}}</ref> The upper areas of the [[neurocranium|cranial bones]] form the [[calvaria (skull)|calvaria]] (skullcap). The facial skeleton (membranous viscerocranium) is formed by the bones supporting the face, and includes the [[mandible]]. 

The bones of the skull are joined by [[fibrous joint]]s known as sutures—[[synarthrodial]] (immovable) [[joint]]s formed by bony [[ossification]], with [[Sharpey's fibres]] permitting some flexibility. Sometimes there can be extra bone pieces within the suture known as [[Wormian bone]]s or ''sutural bones''. Most commonly these are found in the course of the [[lambdoid suture]].

====Bones ====
{{main|Bone}}

The human skull is generally considered to consist of 22 bones—eight cranial bones and fourteen facial skeleton bones. In the neurocranium these are the [[occipital bone]], two [[temporal bone]]s, two [[parietal bone]]s, the [[sphenoid bone|sphenoid]], [[ethmoid bone|ethmoid]] and [[frontal bone]]s.

The bones of the [[facial skeleton]] (14) are the [[vomer]], two [[inferior nasal concha]]e, two [[nasal bone]]s, two [[maxilla]], the mandible, two [[palatine bone]]s, two [[zygomatic bone]]s, and two [[lacrimal bone]]s. Some sources count a paired bone as one, or the maxilla as having two bones (as its parts); some sources include the [[hyoid bone]] or the three [[ossicles]] of the [[middle ear]], the malleus, incus, and stapes, but the overall general consensus of the number of bones in the human skull is the stated twenty-two.

Some of these bones—the occipital, parietal, frontal, in the neurocranium, and the nasal, lacrimal, and vomer, in the facial skeleton are [[flat bone]]s.

====Cavities and foramina====
[[File:3d CT scan animation.gif|thumb|upright=.8|CT scan of a human skull in 3D]]

The skull also contains [[Sinus (anatomy)|sinuses]], air-filled cavities known as [[paranasal sinuses]], and numerous [[List of foramina in the human body#Skull|foramina]]. The sinuses are lined with [[respiratory epithelium]]. Their known functions are the lessening of the weight of the skull, the aiding of resonance to the voice and the warming and moistening of the air drawn into the [[nasal cavity]].

The foramina are openings in the skull. The largest of these is the [[foramen magnum]], of the occipital bone, that allows the passage of the [[spinal cord]] as well as [[nerve]]s and [[blood vessel]]s.

====Processes====
The many [[Process (anatomy)#Examples|processes]] of the skull include the [[mastoid process]] and the [[zygomatic process]]es.

=== Other vertebrates ===
==== Fenestrae====
[[File:Chimpanzee skull.jpg|thumb|upright=.7|left|Chimpanzee skull]]
{|
|
The [[Fenestra (anatomy)|fenestrae]] (from Latin, meaning ''windows'') are openings in the skull.
* [[Antorbital fenestra]]
* [[Mandibular]] fenestra
* [[Quadratojugal]] fenestra
* [[Subsquamosal fenestra]], an opening between two parts of the [[squamosal bone]] in some rodents
* [[Temporal fenestra]]
|}

==== Bones ====
The [[jugal]] is a skull bone that found in most of the reptiles, amphibians and birds. In mammals, the jugal is often called the zygomatic bone or malar bone.<ref>{{cite journal |last1=Dechow |first1=Paul C. |last2=Wang |first2=Qian |title=Evolution of the Jugal/Zygomatic Bones |journal=The Anatomical Record |date=January 2017 |volume=300 |issue=1 |pages=12–15 |doi=10.1002/ar.23519 |pmid=28000397 }}</ref>

The [[prefrontal bone]] is a bone that separates the lacrimal and frontal bones in many tetrapod skulls.

====Fish====
[[File:FishKeyDay.jpg|thumb|upright=.8|Fish head parts, 1889, Fauna of British India, Sir Francis Day]]

The skull of fish is formed from a series of only loosely connected bones. [[Lamprey]]s and [[shark]]s only possess a cartilaginous endocranium, with both the upper jaw and the lower [[jaw]]s being separate elements. Bony fishes have additional [[dermal bone]], forming a more or less coherent [[skull roof]] in [[lungfish]] and [[holost]] fish. The lower jaw defines the chin.

The simpler structure is found in [[jawless fish]], in which the cranium is normally represented by a trough-like basket of cartilaginous elements only partially enclosing the brain, and associated with the capsules for the inner ears and the single nostril. Distinctively, these fish have no jaws.<ref name="VB2" />

[[Cartilaginous fish]], such as sharks and rays, have also simple, and presumably primitive, skull structures. The cranium is a single structure forming a case around the brain, enclosing the lower surface and the sides, but always at least partially open at the top as a large [[fontanelle]]. The most anterior part of the cranium includes a forward plate of cartilage, the [[rostrum (anatomy)|rostrum]], and capsules to enclose the [[olfactory]] organs. Behind these are the orbits, and then an additional pair of capsules enclosing the structure of the [[inner ear]]. Finally, the skull tapers towards the rear, where the foramen magnum lies immediately above a single [[Condyle (anatomy)|condyle]], articulating with the first [[vertebra]]. There are, in addition, at various points throughout the cranium, smaller [[Foramina of skull|foramina]] for the cranial nerves. The jaws consist of separate hoops of cartilage, almost always distinct from the cranium proper.<ref name="VB2">{{cite book |last1=Romer |first1=Alfred Sherwood |first2=Parsons |last2=Thomas S. |year=1977 |title=The Vertebrate Body |publisher=Holt-Saunders International |location= Philadelphia, PA |pages=173–177 |isbn= 0-03-910284-X}}</ref>

[[File:Xiphias gladius 7zz.jpg|thumb|left|Skull of a [[swordfish]]]]

In [[ray-finned fish]], there has also been considerable modification from the primitive pattern. The roof of the skull is generally well formed, and although the exact relationship of its bones to those of tetrapods is unclear, they are usually given similar names for convenience. Other elements of the skull, however, may be reduced; there is little cheek region behind the enlarged orbits, and little, if any bone in between them. The upper jaw is often formed largely from the [[premaxilla]], with the maxilla itself located further back, and an additional bone, the symplectic, linking the jaw to the rest of the cranium.<ref name="VB"/>

Although the skulls of fossil lobe-finned fish resemble those of the early tetrapods, the same cannot be said of those of the living [[lungfish]]es. The [[skull roof]] is not fully formed, and consists of multiple, somewhat irregularly shaped bones with no direct relationship to those of tetrapods. The upper jaw is formed from the [[pterygoid bone|pterygoid]]s and [[vomer]]s alone, all of which bear teeth. Much of the skull is formed from [[cartilage]], and its overall structure is reduced.<ref name="VB" />

===Tetrapods===
The skulls of the earliest [[tetrapod]]s closely resembled those of their [[ancestor]]s amongst the [[lobe-finned fish]]es. The [[skull roof]] is formed of a series of plate-like bones, including the maxilla, [[frontal bone|frontals]], [[parietal bone|parietal]]s, and [[lacrimal bone|lacrimal]]s, among others. It is overlaying the [[endocranium]], corresponding to the cartilaginous skull in sharks and [[Batoidea|rays]]. The various separate bones that compose the temporal bone of humans are also part of the skull roof series. A further plate composed of four pairs of bones forms the roof of the mouth; these include the [[vomer]] and [[palatine bone]]s. The base of the cranium is formed from a ring of bones surrounding the foramen magnum and a median bone lying further forward; these are [[homology (biology)|homologous]] with the occipital bone and parts of the sphenoid in mammals. Finally, the lower jaw is composed of multiple bones, only the most anterior of which (the dentary) is homologous with the mammalian mandible.<ref name="VB">{{cite book |last1=Romer |first1=Alfred Sherwood |last2=Parsons |first2=Thomas S. |year=1977 |title=The Vertebrate Body |publisher=Holt-Saunders International |location= Philadelphia, PA |pages=216–247 |isbn=0-03-910284-X}}</ref>

In living tetrapods, a great many of the original bones have either disappeared or fused into one another in various arrangements.

====Birds====
[[File:CuckooSkull.jpg|thumb|Cuckoo skull]]

[[Bird]]s have a [[diapsid]] skull, as in reptiles, with a prelacrimal fossa (present in some reptiles). The skull has a single occipital condyle.<ref>{{Cite book|url=https://archive.org/details/naturalhistoryof033252mbp|title=Natural History of Birds|last=Wing|first=Leonard W.|publisher=The Ronald Press Company|year=1956|pages=[https://archive.org/details/naturalhistoryof033252mbp/page/n25 22]–23|chapter=The Place of Birds in Nature}}</ref> The skull consists of five major bones: the frontal (top of head), parietal (back of head), premaxillary and nasal (top beak), and the mandible (bottom beak). The skull of a normal bird usually weighs about 1% of the bird's total bodyweight. The eye occupies a considerable amount of the skull and is surrounded by a sclerotic eye-ring, a ring of tiny bones. This characteristic is also seen in reptiles.

====Amphibians====
[[File:AmphibSkeletons.png|thumb|upright=.8|Amphibians' skulls, Hans Gadow, 1909 ''Amphibia and Reptiles'']]

Living [[amphibian]]s typically have greatly reduced skulls, with many of the bones either absent or wholly or partly replaced by cartilage.<ref name="VB" /> In mammals and birds, in particular, modifications of the skull occurred to allow for the expansion of the brain. The fusion between the various bones is especially notable in birds, in which the individual structures may be difficult to identify.