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The skull is a
bone A bone is a rigid tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North America * ''Triphosa dubit ...

bone
structure that forms the head in
vertebrates Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic ma ...

vertebrates
. It supports the structures of the face and provides a protective cavity for the brain. The skull is composed of two parts: the cranium and the
mandible In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any ind ...

mandible
. In
human Humans (''Homo sapiens'') are the most abundant and widespread species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A speci ...

human
s, these two parts are the
neurocranium In human anatomy, the neurocranium, also known as the braincase, brainpan, or brain-pan is the upper and back part of the skull, which forms a protective case around the brain A brain is an organ (anatomy), organ that serves as the center of th ...
and the viscerocranium (
facial skeleton The facial skeleton comprises the ''facial bones'' that may attach to build a portion of the skull The skull is a bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. ...
) that includes the mandible as its largest bone. The skull forms the anterior-most portion of the
skeleton A skeleton is a structural frame that supports an animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consu ...

skeleton
and is a product of
cephalisation Cephalization is an evolution Evolution is change in the Heredity, heritable Phenotypic trait, characteristics of biological populations over successive generations. These characteristics are the Gene expression, expressions of genes that are ...
—housing the brain, and several sensory structures such as the eyes, ears, nose, and mouth. In humans these sensory structures are part of the facial skeleton. Functions of the skull include protection of the brain, fixing the distance between the eyes to allow
stereoscopic vision Kaiserpanorama consists of a multi-station viewing apparatus and sets of stereo slides. Patented by A. Fuhrmann around 1890. Stereoscopy (also called stereoscopics, or stereo imaging) is a technique for creating or enhancing the illusion ...
, and fixing the position of the ears to enable
sound localisation Sound localization is a listener's ability to identify the location or origin of a detected sound In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'natur ...
of the direction and distance of sounds. In some animals, such as horned
ungulate Ungulates ( ) are members of the diverse Ungulata which primarily consists of large mammals with . These include s such as s, es, and s; and s such as , s, s, s, , , and es. s such as , , and are also classified as even-toed ungulates, althoug ...
s (mammals with hooves), the skull also has a defensive function by providing the mount (on the
frontal bone The frontal bone is a bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. Bones protect the various organs of the body, produce red blood cell, red and white blood cells, ...

frontal bone
) for the
hornsHorns or The Horns may refer to: * The Horns (Colorado), a summit on Cheyenne Mountain * ''Horns'' (novel), a dark fantasy novel written in 2010 by Joe Hill ** ''Horns'' (film), a 2013 film adaptation of Hill's novel * "The Horns" (song), a 2015 ...
. The English word ''skull'' is probably derived from
Old Norse Old Norse, Old Nordic, or Old Scandinavian is a stage of development of North Germanic dialects before their final divergence into separate Nordic languages. Old Norse was spoken by inhabitants of Scandinavia Scandinavia; : ''Skades ...
, while the
Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Republic, it became ...

Latin
word comes from the
Greek root Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 million as of 2018; Athens is ...
(). The skull is made up of a number of fused
flat bone Flat bones are bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. Bones protect the various organs of the body, produce red blood cell, red and white blood cells, store ...
s, and contains many
foramina In anatomy and osteology, a foramen (;Entry "foramen"
in
fossae,
processes A process is a series or set of Action (philosophy), activities that interact to produce a result; it may occur once-only or be recurrent or periodic. Things called a process include: Business and management *Business process, activities that pro ...
, and several cavities or
sinuses Paranasal sinuses are a group of four paired air-filled spaces that surround the nasal cavity The nasal cavity is a large, air-filled space above and behind the nose A nose is a protuberance in vertebrate Vertebrates () comprise all speci ...
. In
zoology Zoology ()The pronunciation of zoology as is usually regarded as nonstandard, though it is not uncommon. is the branch of biology that studies the Animal, animal kingdom, including the anatomy, structure, embryology, evolution, Biological class ...
there are openings in the skull called
fenestra A fenestra (fenestration; plural fenestrae or fenestrations) is any small opening or pore, commonly used as a term in the biological sciences Biology is the natural science Natural science is a branch of science Science (from th ...
e.


Structure


Humans

The human skull is the bone structure that forms the
head Head Sport GmbH is an American-Austrian manufacturing company Manufacturing is the creation or production Production may be: Economics and business * Production (economics) * Production, the act of manufacturing goods * Production, in th ...

head
in the
human skeleton The human skeleton is the internal framework of the human body. It is composed of around 270 bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. Bones protect the var ...

human skeleton
. It supports the structures of the
face The face is the front of an animal's head that features the eyes Eyes are organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tis ...
and forms a cavity for the
brain A brain is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tiss ...

brain
. Like the skulls of other vertebrates, it protects the brain from injury. The skull consists of three parts, of different
embryological Embryology (from Greek ἔμβρυον, ''embryon'', "the unborn, embryo An embryo is the early stage of development of a multicellular organism. In general, in organism In biology, an organism (from Ancient Greek, Greek: ὀργ ...
origin—the
neurocranium In human anatomy, the neurocranium, also known as the braincase, brainpan, or brain-pan is the upper and back part of the skull, which forms a protective case around the brain A brain is an organ (anatomy), organ that serves as the center of th ...
, the sutures, and the
facial skeleton The facial skeleton comprises the ''facial bones'' that may attach to build a portion of the skull The skull is a bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. ...
(also called the ''membraneous viscerocranium''). The neurocranium (or ''braincase'') forms the protective
cranial cavity The cranial cavity, also known as intracranial space, is the space within the skull The skull is a bone A bone is a rigid tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a s ...
that surrounds and houses the brain and
brainstem The brainstem (or brain stem) is the posterior stalk-like part of the brain A brain is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and anima ...

brainstem
. The upper areas of the
cranial bones Standard anatomical terms of location deal unambiguously with the anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient ...
form the calvaria (skullcap). The membranous viscerocranium includes the
mandible In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any ind ...

mandible
. The sutures are fairly rigid joints between bones of the neurocranium. The facial skeleton is formed by the bones supporting the face.


Bones

Except for the
mandible In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any ind ...
, all of the bones of the skull are joined together by
sutures Suture, literally meaning "seam", may refer to: Arts, entertainment, and media * Suture (album), ''Suture'' (album), a 2000 album by American Industrial rock band Chemlab * Suture (film), ''Suture'' (film), a 1993 film directed by Scott McGehee and ...

sutures
synarthrodial (immovable)
joints A joint or articulation (or articular surface) is the connection made between bone A bone is a rigid tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Trip ...

joints
formed by bony
ossification Ossification (or osteogenesis) in bone remodeling is the process of laying down new bone material by Cell (biology), cells named osteoblasts. It is synonymous with bone tissue formation. There are two processes resulting in the formation of no ...
, with
Sharpey's fibres Sharpey's fibres (bone fibres, or perforating fibres) are a matrix of connective tissue Connective tissue is one of the four basic types of animal tissue (biology), tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It deve ...
permitting some flexibility. Sometimes there can be extra bone pieces within the suture known as wormian bones or ''sutural bones''. Most commonly these are found in the course of the
lambdoid suture#REDIRECT Lambdoid suture The lambdoid suture (or lambdoidal suture) is a dense, fibrous connective tissue Connective tissue is one of the four basic types of animal tissue (biology), tissue, along with epithelial tissue, muscle tissue, and nervous ...

lambdoid suture
. The human skull is generally considered to consist of twenty-two
bone A bone is a rigid tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North America * ''Triphosa dubit ...

bone
s—eight cranial bones and fourteen facial skeleton bones. In the neurocranium these are the
occipital bone The occipital bone () is a neurocranium, cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is Trapezoid, trapezoidal in shape and curved on itself like a shallow dish. The occipital bone overlies the occi ...

occipital bone
, two
temporal bone The temporal bones are situated at the sides and base of the skull The skull is a bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the vertebrate skeleton in animals. Bones protect the various organs of ...

temporal bone
s, two
parietal bone The parietal bones () are two bones in the skull The skull is a bone A bone is a rigid tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesi ...

parietal bone
s, the ,
ethmoid The ethmoid bone (; from Greek ''ethmos'', "sieve") is an unpaired bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. Bones protect the various organs of the body, produ ...
and
frontal bone The frontal bone is a bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. Bones protect the various organs of the body, produce red blood cell, red and white blood cells, ...

frontal bone
s. The bones of the
facial skeleton The facial skeleton comprises the ''facial bones'' that may attach to build a portion of the skull The skull is a bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. ...
(14) are the
vomer The vomer () is one of the unpaired facial skeleton, facial bones of the human skull, skull. It is located in the midsagittal line, and Articulation (anatomy), articulates with the sphenoid bone, sphenoid, the ethmoid bone, ethmoid, the left and r ...

vomer
, two
inferior nasal concha The inferior nasal concha (inferior turbinated bone or inferior turbinal/turbinate) is one of the three paired nasal concha In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the struc ...
e, two
nasal bone The nasal bones are two small oblong bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. Bones protect the various organs of the body, produce red blood cell, red and whi ...

nasal bone
s, two
maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The tw ...

maxilla
, the
mandible In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any ind ...

mandible
, two
palatine bone In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of concerned with the study of the structure of s and their parts. Anatomy is a branch of natural science which deals with the structural organization of living things. It i ...

palatine bone
s, two
zygomatic bone In the human skull The skull is a bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. Bones protect the various organs of the body, produce red blood cell, red and ...

zygomatic bone
s, and two
lacrimal bone The lacrimal bone is a small and fragile bone A bone is a rigid tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer ...

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 The hyoid bone (lingual bone or tongue-bone) () is a horseshoe A horseshoe is a fabricated product, normally made of metal A metal (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ε ...
or the three
ossicles The ossicles (also called auditory ossicles) are three bone A bone is a rigid tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a spe ...
of the
middle ear The middle ear is the portion of the ear The ear is the organ of hearing and, in mammals, balance. In mammals, the ear is usually described as having three parts—the outer ear The outer ear, external ear, or auris externa is th ...

middle ear
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 Flat bones are bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. Bones protect the various organs of the body, produce red blood cell, red and white blood cells, store ...
s.


Cavities and foramina

The skull also contains
sinuses Paranasal sinuses are a group of four paired air-filled spaces that surround the nasal cavity The nasal cavity is a large, air-filled space above and behind the nose A nose is a protuberance in vertebrate Vertebrates () comprise all speci ...
, air-filled cavities known as
paranasal sinuses Paranasal sinuses are a group of four paired air-filled spaces that surround the nasal cavity The nasal cavity is a large, air-filled space above and behind the human nose, nose in the middle of the face. The nasal septum divides the cavity int ...

paranasal sinuses
, and numerous
foramina In anatomy and osteology, a foramen (;Entry "foramen"
in
. The sinuses are lined with
respiratory epithelium The respiratory system (also respiratory apparatus, ventilatory system) is a biological system A biological system is a complex network which connects several biologically relevant entities. Biological organization spans several scales and are d ...
. 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 nasal cavity is a large, air-filled space above and behind the nose A nose is a protuberance in vertebrates that houses the nostrils, or nares, which receive and expel air for Respiration (physiology), respiration alongside the mouth. Beh ...

nasal cavity
. The foramina are openings in the skull. The largest of these is the
foramen magnum The foramen magnum ( la, great hole) is a large, oval-shaped opening in the occipital bone The occipital bone () is a cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is Trapezoid, trapezoidal in shap ...
that allows the passage of the
spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column. It encloses the central canal of the spinal cord, which contain ...

spinal cord
as well as
nerve A nerve is an enclosed, cable-like bundle of fibers (called axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences Despite the various English dialects Dialect The term diale ...

nerve
s and
blood vessel The blood vessels are the components of the circulatory system The circulatory system, also called the cardiovascular system or the vascular system, is an organ system An organ system is a biological system A biological system is a comp ...
s.


Processes

The many
processes A process is a series or set of Action (philosophy), activities that interact to produce a result; it may occur once-only or be recurrent or periodic. Things called a process include: Business and management *Business process, activities that pro ...
of the skull include the
mastoid process The mastoid part of the temporal bone is the posterior (back) part of the temporal bone The temporal bones are situated at the sides and base of the skull, and lateral to the temporal lobes of the cerebral cortex. The temporal bones are overlaid b ...

mastoid process
and the
zygomatic process 200px, As a comparison, this is how the skull looks with almost all of the zygomatic process removed. The zygomatic processes are three processes (protrusions) from other bone A bone is a Stiffness, rigid tissue (anatomy), tissue that const ...
es.


Other vertebrates


Fenestrae

The temporal
fenestrae A fenestra (fenestration; plural fenestrae or fenestrations) is any small opening or pore, commonly used as a term in the biology, biological sciences. It is Latin for the word "window", and is used in various fields to describe a pore in an anat ...
are anatomical features of the skulls of several types of
amniote Amniotes (from Greek ἀμνίον ''amnion'', "membrane surrounding the fetus", earlier "bowl in which the blood of sacrificed animals was caught", from ἀμνός ''amnos'', "lamb") are a clade A clade (; from grc, , ''klados'', "bran ...
s, 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 The ''postorbital'' is one of the bones in vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With ...

postorbital
and
squamosalThe squamosal is a skull bone found in most Reptile, reptiles, Amphibian, amphibians, and Bird, birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and Quadratojugal bone, quadratojugal bones form the cheek series ...
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 are 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 two more advanced lines did: the
synapsid Synapsids are a group of animals that includes mammal Mammals (from Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome ...

synapsid
s (mammal-like reptiles) and the
diapsid Diapsids ("two arches") are a group of amniote tetrapods that developed two holes (temporal fenestra) in each side of their skulls about 300 million years ago during the late Carboniferous period. The diapsids are extremely diverse, and include all ...

diapsid
s (most reptiles and later birds). As time progressed, diapsids' and synapsids' temporal fenestrae became more modified and larger to make stronger bites and more jaw muscles. Dinosaurs, which are diapsids, have large advanced openings, and their descendants, the birds, have temporal fenestrae which have been modified. Synapsids, possess one fenestral opening in the skull, situated to the rear of the orbit. In their descendants, the cynodonts, the orbit fused with the fenestral opening after the latter had started expanding within the
therapsids Therapsida is a major group of eupelycosauria Eupelycosauria is a large clade A clade (; from grc, , ''klados'', "branch"), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic—t ...
. Thus most mammals also have this. Later, primates separated their orbit from ''
temporal fossa The temporal fossa is a fossa (shallow depression) on the side of the human skull, skull bounded by the temporal lines and terminating below the level of the zygomatic arch. Boundaries * Medial: frontal bone, parietal bone, temporal bone, and s ...

temporal fossa
'' by the
postorbital barThe postorbital bar (or postorbital bone) is a bony arched structure that connects the frontal bone of the skull to the zygomatic arch In anatomy, the zygomatic arch, or cheek bone, is a part of the skull formed by the zygomatic process of tempor ...
with haplorhines later evolving the postorbital septum.


=Classification

= There are four types of amniote skull, classified by the number and location of their temporal fenestrae. These are: *
Anapsida An anapsid is an amniote whose skull lacks one or more skull openings (fenestra) near the temples. Traditionally, the Anapsida are the most primitive subclass of reptiles, the ancestral stock from which Synapsida and Diapsida evolved, making an ...
– 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 Diapsids ("two arches") are a group of amniote Amniotes (from Greek ἀμνίον ''amnion'', "membrane surrounding the fetus", earlier "bowl in which the blood of sacrificed animals was caught", from ἀμνός ''amnos'', "lamb") are a cla ...
– two openings Evolutionarily, they are related as follows: *
Amniota Amniotes (from Greek ἀμνίον ''amnion'', "membrane surrounding the fetus", earlier "bowl in which the blood of sacrificed animals was caught", from ἀμνός ''amnos'', "lamb") are a clade A clade (; from grc, , ''klados'', "bran ...

Amniota
**Class Synapsida ***Order ****Class
Mammalia Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and characterized by the presence of mammary glands which in Female#Mammalian female, females produce milk ...

Mammalia
– mammals **(Unranked)
Sauropsida Sauropsida ("lizard faces") is a clade A clade (; from grc, , ''klados'', "branch"), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic—that is, composed of a common ancestor and al ...
– reptiles and birds ***Class
Reptilia Reptiles are tetrapod Tetrapods (; from Greek 'four' and 'foot') are four-limbed animals constituting the superclass Tetrapoda . It includes extant and extinct amphibians, reptiles (including dinosaurs and therefore birds), and synapsids ...

Reptilia
****Subclass
Parareptilia Parareptilia ("at the side of reptiles") is a subclass or clade A clade (; from grc, , ''klados'', "branch"), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic—that is, composed o ...
*****Infraclass
Anapsida An anapsid is an amniote whose skull lacks one or more skull openings (fenestra) near the temples. Traditionally, the Anapsida are the most primitive subclass of reptiles, the ancestral stock from which Synapsida and Diapsida evolved, making an ...
****Subclass
Eureptilia Eureptilia ("true reptiles") is one of the two major clade A clade (; from grc, , ''klados'', "branch"), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic—that is, composed of a c ...
*****Infraclass
Diapsida Diapsids ("two arches") are a group of amniote Amniotes (from Greek ἀμνίον ''amnion'', "membrane surrounding the fetus", earlier "bowl in which the blood of sacrificed animals was caught", from ἀμνός ''amnos'', "lamb") are a cla ...
******Class
Aves Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With ...

Aves
*****Infraclass Euryapsida


Bones

The
jugal The jugal is a skull The skull is a bone A bone is a rigid tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer ...
is a skull bone found in most reptiles, amphibians, and birds. In mammals, the jugal is often called the
zygomatic bone In the human skull The skull is a bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. Bones protect the various organs of the body, produce red blood cell, red and ...

zygomatic bone
or malar bone. The
prefrontal bone The prefrontal bone is a bone separating the lacrimal bone, lacrimal and frontal bones in many tetrapod skulls. It first evolution, evolved in the sarcopterygian clade Rhipidistia, which includes lungfish and the Tetrapodomorpha. The prefrontal is ...
is a bone separating the lacrimal and frontal bones in many tetrapod skulls.


Fish

The skull of fishes is formed from a series of only loosely connected bones.
Lamprey Lampreys (sometimes inaccurately called lamprey eels) are an ancient extant lineage of Agnatha, jawless fish of the order (biology), order Petromyzontiformes , placed in the superclass Cyclostomata. The adult lamprey may be characterized by ...

Lamprey
s and sharks only possess a cartilaginous endocranium, with both the upper and lower
jaw The jaw is any opposable articulated structure at the entrance of the , typically used for grasping and manipulating food. The term ''jaws'' is also broadly applied to the whole of the structures constituting the vault of the mouth and serving t ...

jaw
s being separate elements. Bony fishes have additional
dermal bone A dermal bone or investing bone or membrane bone is a bony structure derived from intramembranous ossification Intramembranous ossification is one of the two essential processes during fetal A fetus American and British English spelling diffe ...
, forming a more or less coherent
skull roof The skull roof, or the roofing bones of the skull The skull is a bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the vertebrate skeleton in animals. Bones protect the various organs of the body, produce ...
in
lungfish Lungfish are freshwater rhipidistian vertebrates belonging to the Order (taxonomic rank), order Dipnoi. Lungfish are best known for retaining ancestral characteristics within the Osteichthyes, including the ability to breathe air, and ancestral ...
and
holost Holostei is a group of ray-finned Actinopterygii (New Latin ('having rays') + Greek ( 'wing, fins')), members of which are known as ray-finned fishes, is a clade (traditionally Class (biology), class or subclass) of the Osteichthyes, bony fi ...
fish. The lower jaw defines a 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. 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. 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 The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The tw ...

maxilla
itself located further back, and an additional bone, the symplectic, linking the jaw to the rest of the cranium. 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 Lungfish are freshwater rhipidistian vertebrates belonging to the Order (taxonomic rank), order Dipnoi. Lungfish are best known for retaining ancestral characteristics within the Osteichthyes, including the ability to breathe air, and ancestral ...
es. The
skull roof The skull roof, or the roofing bones of the skull The skull is a bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the vertebrate skeleton in animals. Bones protect the various organs of the body, produce ...
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, pterygoids and
vomer The vomer () is one of the unpaired facial skeleton, facial bones of the human skull, skull. It is located in the midsagittal line, and Articulation (anatomy), articulates with the sphenoid bone, sphenoid, the ethmoid bone, ethmoid, the left and r ...

vomer
s alone, all of which bear teeth. Much of the skull is formed from cartilage, and its overall structure is reduced.


=Tetrapods

= The skulls of the earliest tetrapods closely resembled those of their ancestors amongst the lobe-finned fishes. The
skull roof The skull roof, or the roofing bones of the skull The skull is a bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the vertebrate skeleton in animals. Bones protect the various organs of the body, produce ...
is formed of a series of plate-like bones, including the
maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The tw ...

maxilla
, frontal bone, frontals, parietal bone, parietals, and lacrimal bone, lacrimals, 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 The temporal bones are situated at the sides and base of the skull The skull is a bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the vertebrate skeleton in animals. Bones protect the various organs of ...

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 The vomer () is one of the unpaired facial skeleton, facial bones of the human skull, skull. It is located in the midsagittal line, and Articulation (anatomy), articulates with the sphenoid bone, sphenoid, the ethmoid bone, ethmoid, the left and r ...

vomer
and
palatine bone In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of concerned with the study of the structure of s and their parts. Anatomy is a branch of natural science which deals with the structural organization of living things. It i ...

palatine bone
s. The base of the cranium is formed from a ring of bones surrounding the
foramen magnum The foramen magnum ( la, great hole) is a large, oval-shaped opening in the occipital bone The occipital bone () is a cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is Trapezoid, trapezoidal in shap ...
and a median bone lying further forward; these are homology (biology), homologous with the
occipital bone The occipital bone () is a neurocranium, cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is Trapezoid, trapezoidal in shape and curved on itself like a shallow dish. The occipital bone overlies the occi ...

occipital bone
and parts of the 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 In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any ind ...

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


Birds

Birds have a
diapsid Diapsids ("two arches") are a group of amniote tetrapods that developed two holes (temporal fenestra) in each side of their skulls about 300 million years ago during the late Carboniferous period. The diapsids are extremely diverse, and include all ...

diapsid
skull, as in reptiles, with a prelacrimal fossa (present in some reptiles). The skull has a single occipital condyle. 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

Living amphibians typically have greatly reduced skulls, with many of the bones either absent or wholly or partly replaced by cartilage. 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

The skull is a complex structure; its bones are formed both by intramembranous ossification, intramembranous and endochondral ossification. The
skull roof The skull roof, or the roofing bones of the skull The skull is a bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the vertebrate skeleton in animals. Bones protect the various organs of the body, produce ...
bones, comprising the bones of the
facial skeleton The facial skeleton comprises the ''facial bones'' that may attach to build a portion of the skull The skull is a bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. ...
and the sides and roof of the neurocranium, are
dermal bone A dermal bone or investing bone or membrane bone is a bony structure derived from intramembranous ossification Intramembranous ossification is one of the two essential processes during fetal A fetus American and British English spelling diffe ...
s formed by intramembranous ossification, though the
temporal bone The temporal bones are situated at the sides and base of the skull The skull is a bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the vertebrate skeleton in animals. Bones protect the various organs of ...

temporal bone
s are formed by endochondral ossification. The endocranium, the bones supporting the brain (the occipital bone, occipital, , and
ethmoid The ethmoid bone (; from Greek ''ethmos'', "sieve") is an unpaired bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. Bones protect the various organs of the body, produ ...
) are largely formed by endochondral ossification. Thus frontal and parietal bones are purely membranous. The geometry of the base of skull, skull base and its fossae, the anterior cranial fossa, anterior, middle cranial fossa, middle and posterior cranial fossae changes rapidly. The anterior cranial fossa changes especially during the pregnancy, first trimester of pregnancy and skull defects can often develop during this time. 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 frontal bone is a bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. Bones protect the various organs of the body, produce red blood cell, red and white blood cells, ...

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 The occipital bone () is a neurocranium, cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is Trapezoid, trapezoidal in shape and curved on itself like a shallow dish. The occipital bone overlies the occi ...

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), sutures. 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. (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.


Clinical significance

Craniosynostosis is a condition in which one or more of the fibrous Suture (joint), sutures in an infant skull prematurely fuses, and changes the growth pattern of the skull. Because the skull cannot expand perpendicular to the fused suture, it grows more in the parallel direction. Sometimes the resulting growth pattern provides the necessary space for the growing brain, but results in an abnormal head shape and abnormal facial features. 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. A copper beaten skull is a phenomenon wherein intense intracranial pressure disfigures the internal surface of the skull. 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 coppersmiths. 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 hard unyieldingness; the skull is one of the least deformable structures found in nature with it needing the force of about 1 ton to reduce the diameter of the skull by 1 cm. In some cases, however, of head injury, 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 The foramen magnum ( la, great hole) is a large, oval-shaped opening in the occipital bone The occipital bone () is a cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is Trapezoid, trapezoidal in shap ...
("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. 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. 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. A study conducted in 2018 by the researchers of Harvard Medical School in Boston, funded by National Institutes of Health, 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.


Transgender procedures

Surgical alteration of sexual dimorphism, sexually dimorphic skull features may be carried out as a part of facial feminization surgery, a set of reconstructive surgical procedures that can alter male facial features to bring them closer in shape and size to typical female facial features. These procedures can be an important part of the treatment of transgender people for gender dysphoria.World Professional Association for Transgender Health
WPATH Clarification on Medical Necessity of Treatment, Sex Reassignment, and Insurance Coverage in the U.S.A.
(2008).
World Professional Association for Transgender Health.
Standards of Care for the Health of Transsexual, Transgender, and Gender Nonconforming People, Version 7.
'' pg. 58 (2011).


Society and culture

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.


Osteology

Like the face, the skull and teeth can also indicate a person's life history and origin. Forensics, Forensic scientists and archeology, archaeologists use Metric (mathematics), metric and nonmetric 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 mounds 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. 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.


Sexual dimorphism

In the mid-nineteenth century, anthropologists 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. 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. 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. 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. However, later studies show that women's skulls are slightly thicker and thus men may be more susceptible to head injury than women. However, other studies shows that men skulls are slightly thicker in certain areas. As well as some studies showing that females are more susceptible to head injury (concussion) than males. 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. Male skulls can have more prominent supraorbital ridges, a more prominent glabella, and more prominent parietal bone, temporal lines. Female skulls generally have rounder Orbit (anatomy), orbits, and narrower jaws. Male skulls on average have larger, broader palates, squarer Orbit (anatomy), orbits, larger
mastoid process The mastoid part of the temporal bone is the posterior (back) part of the temporal bone The temporal bones are situated at the sides and base of the skull, and lateral to the temporal lobes of the cerebral cortex. The temporal bones are overlaid b ...

mastoid process
es, larger Paranasal sinus, sinuses, and larger occipital condyles than those of females. Male Human mandible, mandibles typically have squarer chins and thicker, rougher muscle attachments than female mandibles.


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


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, 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.


Additional images


See also

*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


References


External links


Skull Module
(California State University Department of Anthology)
Skull Anatomy Tutorial.
(GateWay Community College)
Bird Skull Collection
Bird skull database with very large collection of skulls (Agricultural University of Wageningen)

(in German)
Human Skulls / Anthropological Skulls / Comparison of Skulls of Vertebrates
(PDF; 502 kB) {{Portal bar, Anatomy Skull, Vertebrate anatomy Flat bones Bones of the head and neck Human head and neck