View source for Skull

{{Short description|Bony structure that forms the head in vertebrates}}
{{About|the skulls of all animals including humans||Skull (disambiguation)|and|Cranium (disambiguation)}}
{{Distinguish|Scull|Sköll}}
{{Use dmy dates|date=April 2017}}
{{Infobox anatomy
| Name            = Skull
| System          = [[Skeletal system]]
| image           = Anatomy of the Human Bone 22.jpg
| Caption         = [[Volume rendering]] of a human head skull from side
| Image2          = 
| Caption2        = 
| IsPartOf        =
| Components      =
| Artery          =
| Vein            =
}}

The '''skull''', or '''cranium''', is typically a [[Bone|bony]] enclosure around the [[brain]] of a [[vertebrate]].<ref name="NCI2024">{{cite web |title=Cranium |url=https://www.cancer.gov/publications/dictionaries/cancer-terms/def/cranium |website=www.cancer.gov |access-date=25 November 2024 |language=en |date=2 February 2011}}</ref><ref name="MW2024">{{cite web |title=Thesaurus results for Skull |url=https://www.merriam-webster.com/thesaurus/skull |website=www.merriam-webster.com |access-date=25 November 2024 |language=en |date=21 November 2024}}</ref> In some [[fish]] and [[amphibian]]s, the skull is of [[cartilage]]. The skull is at the [[head]] end of the vertebrate. 

In the  human, the skull comprises two prominent parts: the [[neurocranium]] and the [[facial skeleton]],<ref>{{Cite book|first1=Tim D. |last1=White |first2=Michael T. |last2=Black |first3=Pieter Arend |last3= Folkens|title=Human Osteology (3rd ed.)|publisher=Academic Press|date=2011-01-21|page =51|isbn =978-0-08-092085-6|url =https://books.google.com/books?id=oCSG2mYlD90C&dq=Human+Osteology+Tim+D.+White+PAGE+51&pg=PP1}}</ref> which [[evolution|evolve]]d from the [[first pharyngeal arch]]. The skull forms the frontmost portion of the [[axial skeleton]] and is a product of [[cephalization]] and [[brain vesicle|vesicular enlargement]] of the brain, with several [[special senses]] structures such as the [[eye]]s, [[ear]]s, [[nose]], [[tongue]] and, in fish, specialized [[touch|tactile]] [[organ (biology)|organ]]s such as [[barbel (zoology)|barbel]]s near the mouth.<ref>{{cite web|url=https://www.britannica.com/science/cephalization|title=Cephalization: Biology|website=[[Encyclopædia Britannica]]|archive-url=https://web.archive.org/web/20160502000749/http://www.britannica.com/science/cephalization|archive-date=2 May 2016|url-status=live|access-date=23 April 2016}}</ref>

The skull is composed of three types of bone: cranial bones, [[facial bone]]s and [[ossicle]]s, which is made up of a number of fused [[flat bone|flat]] and [[irregular bone]]s. The cranial bones are joined at firm fibrous junctions called [[suture (joint)|sutures]] and contains many [[foramina]], [[fossa (anatomy)|fossae]], [[process (anatomy)|processes]], and [[sinus (anatomy)|sinuses]]. In [[zoology]], the openings in the skull are called [[fenestra]]e, the most prominent of which is the [[foramen magnum]], where the [[brainstem]] goes through to join the [[spinal cord]].

In [[human anatomy]], the neurocranium (or braincase), is further divided into the [[Calvaria (skull)|calvaria]] and the [[endocranium]], together forming a [[cranial cavity]] that houses the brain. The interior [[periosteum]] forms part of the [[dura mater]], the facial skeleton and [[splanchnocranium]] with the mandible being its largest bone. The mandible [[joint|articulate]]s with the [[temporal bone]]s of the neurocranium at the paired [[temporomandibular joint]]s. The skull itself articulates with the [[spinal column]] at the [[atlanto-occipital joint]]. The human skull fully develops two years after birth.

Functions of the skull include physical protection for the brain, providing attachments for [[neck]] [[muscle]]s, [[facial muscles]] and [[muscles of mastication]], providing fixed [[eye socket]]s and [[outer ear]]s ([[ear canal]]s and [[auricle (anatomy)|auricle]]s) to enable [[stereoscopic vision]] and [[sound localisation]], forming [[nasal cavity|nasal]] and [[oral cavity|oral cavities]] that allow better [[olfaction]], [[taste]] and [[digestion]], and contributing to [[list of animal sounds|phonation]] by [[acoustic resonance]] within the cavities and sinuses. In some animals such as [[ungulate]]s and [[elephant]]s, the skull also has a function in [[anti-predator defense]] and [[sexual selection]] by providing the foundation for [[horn (anatomy)|horn]]s, [[antler]]s and [[tusk]]s.

The English word ''skull'' is probably derived from [[List of English words of Old Norse origin|Old Norse]] {{Lang|non|skulle}},<ref>{{Cite web|title=Definition of skull {{!}} Dictionary.com|url=https://www.dictionary.com/browse/skull|access-date=2021-09-06|website=www.dictionary.com|language=en}}</ref> while the [[Latin]] word {{Lang|la|cranium}} comes from the [[Greek and Latin roots in English|Greek root]] {{Lang|grc|κρανίον}} ({{Lang|grc-latn|kranion}}). 

{{toclimit|4}}

==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: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=978-0-375-76342-7|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=978-3-030-15363-2|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.

==Development==
[[File:Sobo 1909 104.png|thumb|Skull of a new-born child from the side]]
The skull is a complex structure; its bones are formed both by [[intramembranous ossification|intramembranous]] and [[endochondral ossification]]. The [[skull roof]] bones, comprising the bones of the facial skeleton and the sides and roof of the neurocranium, are [[dermal bone]]s formed by intramembranous ossification, though the temporal bones are formed by endochondral ossification. The [[endocranium]], the bones supporting the brain (the occipital, [[sphenoid bone|sphenoid]], and [[ethmoid bone|ethmoid]]) are largely formed by endochondral ossification. Thus frontal and parietal bones are purely membranous.<ref>{{cite book|title=Human Embryology & Developmental Biology|last=Carlson|first=Bruce M.|publisher=Mosby|year=1999|isbn=0-8151-1458-3|edition=Second|pages=166–170}}</ref> The geometry of the [[base of skull|skull base]] and its [[fossa (anatomy)|fossae]], the [[anterior cranial fossa|anterior]], [[middle cranial fossa|middle]] and [[posterior cranial fossa]]e changes rapidly. The anterior cranial fossa changes especially during the [[pregnancy|first trimester]] of pregnancy and skull defects can often develop during this time.<ref>{{cite journal|last1=Derkowski|first1=Wojciech|last2=Kędzia|first2=Alicja|last3=Glonek|first3=Michał|year=2003|title=Clinical anatomy of the human anterior cranial fossa during the prenatal period|url=http://www.fm.viamedica.pl/darmowy_pdf.phtml?indeks=25&indeks_art=369|journal=Folia Morphologica|volume=62|issue=3|pages=271–3|pmid=14507064|archive-url=https://web.archive.org/web/20110924041427/http://www.fm.viamedica.pl/darmowy_pdf.phtml?indeks=25&indeks_art=369|archive-date=24 September 2011}}</ref> The prenatal growth of the anterior cranial fossa is not uniform. During the first trimester, there is allometric growth, with the longitudinal dimension increasing from 5 to 17 millimeters between the 8th and 14th week of fetal life. At the same time, the angle of the anterior cranial fossa decreases, and its depth increases towards the middle cranial fossa. In the second trimester, growth continues but becomes more uniform, with only slight changes in the angle of the anterior cranial fossa. There is a gradual decrease in the angle between the lesser wings of the sphenoid bone as the depth of the anterior cranial fossa increases in the frontal plane.<ref>{{Cite journal |last1=Derkowski |first1=Wojciech |last2=Kędzia |first2=Alicja |last3=Dudek |first3=Krzysztof |last4=Glonek |first4=Michał |date=2024-12-27 |title=Morphometric evaluation of the anterior cranial fossa during the prenatal stage in humans and its clinical implications |journal=PLOS ONE |language=en |volume=19 |issue=12 |article-number=e0309184 |doi=10.1371/journal.pone.0309184 |doi-access=free |issn=1932-6203 |pmc=11676864 |pmid=39729454|bibcode=2024PLoSO..1909184D }}</ref>

At birth, the human skull is made up of 44 separate bony elements. During development, many of these bony elements gradually fuse together into solid bone (for example, the [[frontal bone]]). The bones of the [[skull roof|roof of the skull]] are initially separated by regions of dense [[connective tissue]] called [[fontanelles]]. There are six fontanelles: one anterior (or frontal), one posterior (or occipital), two sphenoid (or anterolateral), and two mastoid (or posterolateral). At birth, these regions are fibrous and moveable, necessary for birth and later growth. This growth can put a large amount of tension on the "obstetrical hinge", which is where the [[Squama occipitalis|squamous]] and [[Lateral parts of occipital bone|lateral parts]] of the occipital bone meet. A possible complication of this tension is rupture of the [[great cerebral vein]]. As growth and ossification progress, the connective tissue of the fontanelles is invaded and replaced by bone creating [[Suture (anatomical)|suture]]s. The five sutures are the two [[squamosal suture|squamous sutures]], one [[coronal suture|coronal]], one [[lambdoid suture|lambdoid]], and one [[sagittal suture]]. The posterior fontanelle usually closes by eight weeks, but the anterior fontanel can remain open up to eighteen months. The anterior fontanelle is located at the junction of the frontal and parietal bones; it is a "soft spot" on a baby's forehead. Careful observation will show that you can count a baby's heart rate by observing the pulse pulsing softly through the anterior fontanelle.

The skull in the [[neonate]] is large in proportion to other parts of the body. The facial skeleton is one seventh of the size of the [[calvaria (skull)|calvaria]]. (In the adult it is half the size). The [[base of the skull]] is short and narrow, though the [[inner ear]] is almost adult size.<ref name="Human Anatomy Volume 3">{{cite book|title=BD Chaurasia's Human Anatomy: Regional and Applied Dissection and Clinical|last1=Chaurasia|first1=B. D.|publisher=CBS Publishers & Distributors|year=2013|isbn=978-81-239-2332-1|edition=Sixth|volume=3: Head–Neck Brain|pages=29–30}}</ref>

==Clinical significance==
[[Craniosynostosis]] is a condition in which one or more of the fibrous [[Suture (joint)|sutures]] in an infant skull prematurely fuses,<ref>{{cite web|url=http://www.thefetus.net/page.php?id=340|title=Cloverleaf skull or kleeblattschadel|last1=Silva|first1=Sandra|last2=Jeanty|first2=Philippe|date=1999-06-07|work=TheFetus.net|publisher=MacroMedia|archive-url=https://web.archive.org/web/20080213205927/http://www.thefetus.net/page.php?id=340|archive-date=13 February 2008|access-date=2007-02-03}}</ref> and changes the growth pattern of the skull.<ref name="Brief Review">{{cite journal|last1=Slater|first1=Bethany J.|last2=Lenton|first2=Kelly A.|last3=Kwan|first3=Matthew D.|last4=Gupta|first4=Deepak M.|last5=Wan|first5=Derrick C.|last6=Longaker|first6=Michael T.|date=April 2008|title=Cranial Sutures: A Brief Review|journal=[[Plastic and Reconstructive Surgery]]|volume=121|issue=4|pages=170e–8e|doi=10.1097/01.prs.0000304441.99483.97|pmid=18349596|s2cid=34344899}}</ref> Because the skull cannot expand perpendicular to the fused suture, it grows more in the parallel direction.<ref name="Brief Review" /> Sometimes the resulting growth pattern provides the necessary space for the growing brain, but results in an abnormal head shape and abnormal facial features.<ref name="Brief Review" /> In cases in which the compensation does not effectively provide enough space for the growing brain, craniosynostosis results in increased [[intracranial pressure]] leading possibly to visual impairment, sleeping impairment, eating difficulties, or an impairment of mental development.<ref name="Intracranial pressure">{{cite journal|last1=Gault|first1=David T.|last2=Renier|first2=Dominique|last3=Marchac|first3=Daniel|last4=Jones|first4=Barry M.|date=September 1992|title=Intracranial Pressure and Intracranial Volume in Children with Craniosynostosis|journal=[[Plastic and Reconstructive Surgery]]|volume=90|issue=3|pages=377–81|doi=10.1097/00006534-199209000-00003|pmid=1513883}}</ref>

A [[copper beaten skull]] is a phenomenon wherein intense intracranial pressure disfigures the internal surface of the skull.<ref>{{cite web|url=https://radiopaedia.org/articles/copper-beaten-skull|title=Copper beaten skull|last=Gaillard|first=Frank|website=[[Radiopaedia]]|archive-url=https://web.archive.org/web/20180425234432/https://radiopaedia.org/articles/copper-beaten-skull|archive-date=25 April 2018|url-status=live|access-date=25 April 2018}}</ref> The name comes from the fact that the inner skull has the appearance of having been beaten with a [[ball-peen hammer]], such as is often used by [[coppersmith]]s. The condition is most common in children.

===Injuries and treatment===
Injuries to the brain can be life-threatening. Normally the skull protects the brain from damage through its high resistance to deformation; the skull is one of the least deformable structures found in nature, needing the force of about 1 ton to reduce its diameter by 1&nbsp;cm.<ref>{{Cite journal|last=Holbourn|first=A. H. S.|date=9 October 1943|title=Mechanics of Head Injuries|journal=[[The Lancet]]|volume=242|issue=6267|pages=438–41|doi=10.1016/S0140-6736(00)87453-X}}</ref> In some cases of [[head injury]], however, there can be raised [[intracranial pressure]] through mechanisms such as a [[subdural haematoma]]. In these cases, the raised intracranial pressure can cause herniation of the brain out of the foramen magnum ("coning") because there is no space for the brain to expand; this can result in significant [[brain damage]] or death unless an urgent operation is performed to relieve the pressure. This is why patients with [[concussion]] must be watched extremely carefully. Repeated concussions can activate the structure of skull bones as the brain's protective covering.<ref>{{cite web|url=https://neurosciencenews.com/concussion-skull-thickening-21352/|title=Repeated Concussions Can Thicken the Skull|date=September 2, 2022}}</ref>

Dating back to [[Neolithic]] times, a skull operation called [[trepanning]] was sometimes performed. This involved drilling a ''burr'' hole in the cranium. Examination of skulls from this period reveals that the patients sometimes survived for many years afterward. It seems likely that trepanning was also performed purely for ritualistic or religious reasons. Nowadays this procedure is still used but is normally called a [[craniectomy]].

In March 2013, for the first time in the U.S., researchers replaced a large percentage of a patient's skull with a precision, [[3D printing|3D-printed]] [[polymer]] [[Implant (medicine)|implant]].<ref>{{cite web|url=https://www.medicaldaily.com/3d-printed-polymer-skull-implant-used-first-time-us-244583|title=3D-Printed Polymer Skull Implant Used For First Time in US|date=7 March 2013|website=Medical Daily|archive-url=https://web.archive.org/web/20130928042619/http://www.medicaldaily.com/3d-printed-polymer-skull-implant-used-first-time-us-244583|archive-date=28 September 2013|url-status=live|access-date=24 September 2013}}</ref> About 9 months later, the first complete cranium replacement with a 3D-printed plastic insert was performed on a Dutch woman. She had been suffering from [[hyperostosis]], which increased the thickness of her skull and compressed her brain.<ref>{{cite web|url=https://www.dutchnews.nl/news/2014/03/dutch_hospital_gives_patient_n/|title=Dutch hospital gives patient new plastic skull, made by 3D printer|date=26 March 2014|website=DutchNews.nl|archive-url=https://web.archive.org/web/20140328121216/http://www.dutchnews.nl/news/archives/2014/03/dutch_hospital_gives_patient_n.php|archive-date=28 March 2014|url-status=live}}</ref>

A study conducted in 2018 by the researchers of [[Harvard Medical School]] in Boston, funded by [[National Institutes of Health]] (NIH), suggested that instead of travelling via [[blood]], there are "tiny channels" in the skull through which the [[White blood cell|immune cells]] combined with the [[bone marrow]] reach the areas of [[inflammation]] after an injury to the brain tissues.<ref>{{Cite web|url=https://www.medicalnewstoday.com/articles/322901.php|title=Newly discovered skull channels play role in immunity|last=Cohut|first=Maria|date=29 August 2018|work=[[Medical News Today]]|access-date=30 August 2018|archive-date=29 August 2018|archive-url=https://web.archive.org/web/20180829142649/https://www.medicalnewstoday.com/articles/322901.php}}</ref>

===Transgender procedures===
Surgical alteration of [[sexual dimorphism|sexually dimorphic]] skull features may be carried out as a part of [[facial feminization surgery]] or [[facial masculinization surgery]], these reconstructive surgical procedures that can alter sexually dimorphic facial features to bring them closer in shape and size to facial features of the desired sex.<ref name="SpiegelQoL">{{cite journal|last1=Ainsworth|first1=Tiffiny A.|last2=Spiegel|first2=Jeffrey H.|year=2010|title=Quality of life of individuals with and without facial feminization surgery or gender reassignment surgery|journal=[[Quality of Life Research]]|volume=19|issue=7|pages=1019–24|doi=10.1007/s11136-010-9668-7|pmid=20461468|s2cid=601504}}</ref><ref>{{cite journal|last1=Shams|first1=Mohammad Ghasem|last2=Motamedi|first2=Mohammad Hosein Kalantar|date=9 January 2009|title=Case report: Feminizing the male face|journal=ePlasty|volume=9|pages=e2|pmc=2627308|pmid=19198644}}</ref> These procedures can be an important part of the treatment of [[transgender]] people for [[gender dysphoria]].<ref name="wpathMedNed">World Professional Association for Transgender Health. [http://www.wpath.org/documents/Med%20Nec%20on%202008%20Letterhead.pdf WPATH Clarification on Medical Necessity of Treatment, Sex Reassignment, and Insurance Coverage in the U.S.A.] {{webarchive|url=https://web.archive.org/web/20110930040306/http://www.wpath.org/documents/Med%20Nec%20on%202008%20Letterhead.pdf |date=30 September 2011 }} (2008).</ref><ref name="wpath2011">World Professional Association for Transgender Health. ''[http://www.wpath.org/documents/Standards%20of%20Care%20V7%20-%202011%20WPATH.pdf Standards of Care for the Health of Transsexual, Transgender, and Gender Nonconforming People, Version 7.] {{webarchive|url=https://web.archive.org/web/20120303035205/http://www.wpath.org/documents/Standards%20of%20Care%20V7%20-%202011%20WPATH.pdf |date=3 March 2012 }}'' pg. 58 (2011).</ref>

==Society and culture==
[[File:SSACRAM 116.JPG|thumb|left|upright=.8|Adam was believed to have been buried on [[Mount Calvary]]. Silk embroidery (17th century).]]

[[Artificial cranial deformation]] is a largely historical practice of some cultures. Cords and wooden boards would be used to apply pressure to an infant's skull and alter its shape, sometimes quite significantly. This procedure would begin just after birth and would be carried on for several years.{{Citation needed|date=December 2018}}

===Osteology===
Like the face, the skull and teeth can also indicate a person's life history and origin. [[Forensics|Forensic]] scientists and [[archeology|archaeologist]]s use quantitative and qualitative traits to estimate what the bearer of the skull looked like. When a significant amount of bones are found, such as at [[Spitalfields]] in the UK and [[Jōmon]] [[shell mound]]s in Japan, [[Osteology|osteologists]] can use traits, such as the proportions of length, height and width, to know the relationships of the population of the study with other living or extinct populations.{{Citation needed|date=December 2018}}

The German physician [[Franz Joseph Gall]] in around 1800 formulated the theory of [[phrenology]], which attempted to show that specific features of the skull are associated with certain personality traits or intellectual capabilities of its owner. His theory is now considered to be [[pseudoscience|pseudoscientific]].{{Citation needed|date=December 2018}}

===Sexual dimorphism===
{{main|Sexual dimorphism}}

{{unreliable sources|section|date=November 2022}}
In the mid-nineteenth century, [[anthropologist]]s found it crucial to distinguish between male and female skulls. An anthropologist of the time, [[James McGrigor Allan]], argued that the female brain was similar to that of an animal.<ref name=":0">{{Cite journal|last=Fee|first=Elizabeth|date=Fall 1979|title=Nineteenth-Century Craniology: The Study of the Female Skull|journal=[[Bulletin of the History of Medicine]]|volume=53|issue=3|pages=415–33|pmid=394780}}</ref> This allowed anthropologists to declare that women were in fact more emotional and less rational than men. McGrigor then concluded that women's brains were more analogous to infants, thus deeming them inferior at the time.<ref name=":0" /> To further these claims of female inferiority and silence the feminists of the time, other anthropologists joined in on the studies of the female skull. These cranial measurements are the basis of what is known as [[craniology]]. These cranial measurements were also used to draw a connection between women and black people.<ref name=":0" />

Research has shown that while in early life there is little difference between male and female skulls, in adulthood male skulls tend to be larger and more robust than female skulls, which are lighter and smaller, with a cranial capacity about 10 percent less than that of the male.<ref name="The Interior of the Skull">{{cite web|url=https://www.theodora.com/anatomy/the_interior_of_the_skull.html|title=5d. The Interior of the Skull|work=[[Gray's Anatomy]]|archive-url=https://web.archive.org/web/20140331060529/http://www.theodora.com/anatomy/the_interior_of_the_skull.html|archive-date=31 March 2014|url-status=live|access-date=22 October 2014}}</ref> However, later studies show that women's skulls are slightly thicker and thus men may be more susceptible to head injury than women.<ref>Other Sources:
* {{cite journal |last1=Li |first1=Haiyan |last2=Ruan |first2=Jesse |last3=Xie |first3=Zhonghua |last4=Wang |first4=Hao |last5=Liu |first5=Wengling |title=Investigation of the critical geometric characteristics of living human skulls utilising medical image analysis techniques |journal=International Journal of Vehicle Safety |date=2007 |volume=2 |issue=4 |page=345 |doi=10.1504/IJVS.2007.016747}}
* name="Men May Be More Susceptible To Head Injury Than Women, Study Suggests">{{cite web|url=https://www.sciencedaily.com/releases/2008/01/080121122138.htm|title=Men May Be More Susceptible To Head Injury Than Women, Study Suggests|date=22 January 2008|work=[[ScienceDaily]]|archive-url=https://web.archive.org/web/20120307191220/http://www.sciencedaily.com/releases/2008/01/080121122138.htm|archive-date=7 March 2012|url-status=live|access-date=6 June 2012}}
* {{Cite journal|last1=De Boer|first1=H. H. (Hans)|last2=Van der Merwe|first2=A. E. (Lida)|last3=Soerdjbalie-Maikoe|first3=V. (Vidija)|date=September 2016|title=Human cranial vault thickness in a contemporary sample of 1097 autopsy cases: relation to body weight, stature, age, sex and ancestry|journal=International Journal of Legal Medicine|language=en|volume=130|issue=5|pages=1371–1377|doi=10.1007/s00414-016-1324-5|pmid=26914798|pmc=4976057|issn=0937-9827|doi-access=free}}
* {{Cite journal|last1=Ross|first1=M. D.|last2=Lee|first2=K. A.|last3=Castle|first3=W. M.|date=1976-04-10|title=Skull thickness of Black and White races|journal=South African Medical Journal = Suid-Afrikaanse Tydskrif vir Geneeskunde|volume=50|issue=16|pages=635–638|issn=0256-9574|pmid=1224277}}
* {{cite journal |last1=Adeloye |first1=Adelola |last2=Kattan |first2=Kenneth R. |last3=Silverman |first3=Frederic N. |title=Thickness of the normal skull in the American blacks and whites |journal=American Journal of Physical Anthropology |date=July 1975 |volume=43 |issue=1 |pages=23–30 |doi=10.1002/ajpa.1330430105|pmid=1155589 }}
* {{Cite web|title=International Journal of Research in Medical Sciences|url=https://www.msjonline.org/index.php/ijrms/index|access-date=2021-02-18|website=www.msjonline.org}}
* {{Cite journal|last1=Ekşi|first1=Murat Şakir|last2=Güdük|first2=Mustafa|last3=Usseli|first3=Murat Imre|date=2020-11-19|title=Frontal Bone is Thicker in Women and Frontal Sinus is Larger in Men: A Morphometric Analysis|journal=The Journal of Craniofacial Surgery|volume=32|issue=5|pages=1683–1684|doi=10.1097/SCS.0000000000007256|issn=1536-3732|pmid=33229988|s2cid=227159148}}</ref> However, other studies shows that men's skulls are slightly thicker in certain areas.<ref>{{Cite journal|doi = 10.1186/1746-160X-1-13|title = Thickness of the human cranial diploe in relation to age, sex and general body build|year = 2005|last1 = Lynnerup|first1 = Niels|last2 = Astrup|first2 = Jacob G.|last3 = Sejrsen|first3 = Birgitte|journal = Head & Face Medicine|volume = 1|article-number = 13|pmid = 16364185|pmc = 1351187 | doi-access=free }}</ref> Some studies show that females are more susceptible to concussion than males.<ref>{{Cite journal|url=https://www.tandfonline.com/doi/abs/10.1207/S15324826AN1001_2|doi = 10.1207/S15324826AN1001_2|title = Current Issues in the Identification, Assessment, and Management of Concussions in Sports-Related Injuries|year = 2003|last1 = McKeever|first1 = Catherine K.|last2 = Schatz|first2 = Philip|journal = Applied Neuropsychology|volume = 10|issue = 1|pages = 4–11|pmid = 12734070|s2cid = 33825332|url-access = subscription}}</ref> Men's skulls have also been shown to maintain density with age, which may aid in preventing head injury, while women's skull density slightly decreases with age.<ref>{{Cite journal|last1=Lillie|first1=Elizabeth M.|last2=Urban|first2=Jillian E.|last3=Lynch|first3=Sarah K.|last4=Weaver|first4=Ashley A.|last5=Stitzel|first5=Joel D.|date=2016|title=Evaluation of Skull Cortical Thickness Changes With Age and Sex From Computed Tomography Scans|journal=Journal of Bone and Mineral Research|language=en|volume=31|issue=2|pages=299–307|doi=10.1002/jbmr.2613|pmid=26255873|issn=1523-4681|doi-access=free}}</ref><ref>{{Cite journal|s2cid=39294670|doi=10.1007/s00414-010-0544-3|title=Age and gender-dependent bone density changes of the human skull disclosed by high-resolution flat-panel computed tomography|year=2011|last1=Schulte-Geers|first1=Christina|last2=Obert|first2=Martin|last3=Schilling|first3=René L.|last4=Harth|first4=Sebastian|last5=Traupe|first5=Horst|last6=Gizewski|first6=Elke R.|last7=Verhoff|first7=Marcel A.|journal=International Journal of Legal Medicine|volume=125|issue=3|pages=417–425|pmid=21234583}}</ref>

Male skulls can all have more prominent [[supraorbital ridge]]s, [[glabella]], and [[parietal bone|temporal lines]]. Female skulls generally have rounder [[Orbit (anatomy)|orbit]]s and narrower jaws. Male skulls on average have larger, broader [[palate]]s, squarer orbits, larger [[mastoid process]]es, larger [[Paranasal sinus|sinus]]es, and larger [[occipital condyle]]s than those of females. Male mandibles typically have squarer chins and thicker, rougher muscle attachments than female mandibles.<ref>{{cite journal | pmc=3919368 | date=2013 | last1=G. | first1=V. | last2=Gowri s.r. | first2=M. | last3=J. | first3=A. | title=Sex Determination of Human Mandible Using Metrical Parameters | journal=Journal of Clinical and Diagnostic Research| volume=7 | issue=12 | pages=2671–2673 | doi=10.7860/JCDR/2013/7621.3728 | pmid=24551607 }}</ref>

===Craniometry===
The [[cephalic index]] is the ratio of the width of the head, multiplied by 100 and divided by its length (front to back). The index is also used to categorize animals, especially dogs and cats. The width is usually measured just below the [[parietal eminence]], and the length from the [[glabella]] to the occipital point.

Humans may be:
* ''Dolichocephalic'' — long-headed
* ''Mesaticephalic'' — medium-headed
* ''Brachycephalic'' — short-headed<ref name="Human Anatomy Volume 3"/>
The [[cephalic index#Vertical cephalic index|''vertical'' cephalic index]] refers to the ratio between the height of the head multiplied by 100 and divided by the length of the head.

Humans may be:
* ''Chamaecranic'' — low-skulled
* ''Orthocranic'' — medium high-skulled
* ''Hypsicranic'' — high-skulled

== Terminology ==
* [[Chondrocranium]], a primitive cartilaginous skeletal structure
* [[Endocranium]]
* [[Epicranium]]
* [[Pericranium]], a membrane that lines the outer surface of the cranium

==History==
[[Trepanning]], a practice in which a hole is created in the skull, has been described as the oldest surgical procedure for which there is [[archaeological]] evidence,<ref>{{Cite book |author=Capasso, Luigi |year=2002 |title=Principi di storia della patologia umana: corso di storia della medicina per gli studenti della Facoltà di medicina e chirurgia e della Facoltà di scienze infermieristiche |location=Rome |publisher=SEU |isbn=978-88-87753-65-3 |oclc=50485765 |language=it}}</ref> found in the forms of cave paintings and human remains. At one burial site in [[France]] dated to 6500 BCE, 40 out of 120 [[prehistoric France|prehistoric]] skulls found had trepanation holes.<ref name="restak2000">{{cite book |author=Restak, Richard|chapter=Fixing the Brain |title=Mysteries of the Mind |publisher=National Geographic Society |location=Washington, D.C. |year=2000 |isbn=978-0-7922-7941-9 |oclc=43662032}}</ref>

== Additional images ==
<gallery>
File:African elephant skull - Cleveland Museum of Natural History - 2014-12-26 (21054840471).jpg|[[African elephant]] skull in the [[Cleveland Museum of Natural History]]
File:VautourCrane2.jpg|[[Vulture]] skull
File:Ophiophagus hannah skull.jpg|[[King cobra]] skull
File:Goat skull-FMVZ USP-18.jpeg|Goat skull
File:Tiktaalik skull front.jpg|Skull of ''[[Tiktaalik]]'', an extinct genus transitional between [[lobe-finned fish]] and early tetrapods
File:Centrosaurus.JPG|''[[Centrosaurus]]'' skull
</gallery>

==See also==
{{Anatomy-terms}}
<!-- Please keep entries in alphabetical order & add a short description [[WP:SEEALSO]] -->
{{div col|small=yes|colwidth=20em}}
*[[Craniometry]]
*[[Crystal skull]]
*[[Head and neck anatomy]]
*[[Human skull symbolism]]
*[[Memento mori]]
*[[Plagiocephaly]], the abnormal flattening of one side of the skull
*[[Skull and crossbones (disambiguation)]]
*[[Teshik-Tash#The skull|Teshik-Tash]] 
*[[Totenkopf]]
*[[Yorick]]
*[[Overmodelled skull]]
*[[Diploë]]
{{div col end}}
<!-- please keep entries in alphabetical order -->

== References ==
{{Gray's}}

{{CCBYSA4Source|sourcepath=https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0309184|sourcearticle=Morphometric evaluation of the anterior cranial fossa during the prenatal stage in humans and its clinical implications|revision=1291217525|author(s)=Wojciech Derkowski, Alicja Kędzia, Krzysztof Dudek, Michał Glonek}}
{{reflist}}

== External links ==
{{commons category multi|Animal skulls|Human skulls}}
{{Wiktionary}}
*[https://web.archive.org/web/20180430094506/http://www.csuchico.edu/anth/Module/skull.html Skull Module] ([[California State University]] Department of Anthology)
*[https://web.archive.org/web/20170702211244/http://www.gwc.maricopa.edu/class/bio201/skull/skulltt.htm Skull Anatomy Tutorial.] ([[GateWay Community College]])
*[https://www.skullsite.com Bird Skull Collection] Bird skull database with very large collection of skulls (Agricultural University of Wageningen)
* [http://www.drjastrow.de/WAI/bones/skullbase.html Human skull base] (in German)
* [https://web.archive.org/web/20111119200906/http://www.somso.de/img/schaedel_en.pdf Human Skulls / Anthropological Skulls / Comparison of Skulls of Vertebrates ] (PDF; 502&nbsp;kB)

{{Cranial fibrous joints}}
{{Cranium}}
{{Facial bones}}
{{Compound structures of skull}}
{{Human systems and organs}}
{{Authority control}}

{{Portal bar|Anatomy}}

[[Category:Skull| ]]
[[Category:Vertebrate anatomy]]
[[Category:Flat bones]]
[[Category:Bones of the head and neck]]
[[Category:Human head and neck]]