The skull is a
bone
A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...
protective
cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the
mandible
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...
. In
human
Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, cultu ...
s, these two parts are the
neurocranium and the viscerocranium (
facial skeleton
The facial skeleton comprises the ''facial bones'' that may attach to build a portion of the skull. The remainder of the skull is the braincase.
In human anatomy and development, the facial skeleton is sometimes called the ''membranous visceroc ...
) that includes the mandible as its largest bone. The skull forms the anterior-most portion of the
skeleton
A skeleton is the structural frame that supports the body of an animal. There are several types of skeletons, including the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure inside ...
and is a product of
cephalisation—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, 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 direction and distance.
The sound localization mechanisms of the mammalian auditory system have been extensively studied. The auditory system us ...
of the direction and distance of sounds. In some animals, such as horned
ungulates (mammals with hooves), the skull also has a defensive function by providing the mount (on the
frontal bone
The frontal bone is a bone in the human skull. The bone consists of two portions.'' Gray's Anatomy'' (1918) These are the vertically oriented squamous part, and the horizontally oriented orbital part, making up the bony part of the forehead, ...
) for the
horns.
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 and their overseas settlement ...
, while the
Latin
Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...
word comes from the
Greek root (). The human skull fully develops two years after birth.The junctions of the skull bones are joined by structures called
sutures.
The skull is made up of a number of fused
flat bones, and contains many
foramina,
fossae,
processes
A process is a series or set of 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 produce a specific se ...
, and several cavities or
sinuses
Paranasal sinuses are a group of four paired air-filled spaces that surround the nasal cavity. The maxillary sinuses are located under the eyes; the frontal sinuses are above the eyes; the ethmoidal sinuses are between the eyes and the spheno ...
. 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 kingdom, including the structure, embryology, evolution, classification, habits, an ...
there are openings in the skull called
fenestrae.
Structure
Humans
The human skull is the bone structure that forms the
head
A head is the part of an organism which usually includes the ears, brain, forehead, cheeks, chin, eyes, nose, and mouth, each of which aid in various sensory functions such as sight, hearing, smell, and taste. Some very simple animals ...
in the
human skeleton
The human skeleton is the internal framework of the human body. It is composed of around 270 bones at birth – this total decreases to around 206 bones by adulthood after some bones get fused together. The bone mass in the skeleton makes up a ...
. It supports the structures of the
face and forms a cavity for the
brain
A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as Visual perception, vision. I ...
. Like the skulls of other vertebrates, it protects the brain from injury.
The skull consists of three parts, of different
embryological origin—the
neurocranium, the sutures, and the
facial skeleton
The facial skeleton comprises the ''facial bones'' that may attach to build a portion of the skull. The remainder of the skull is the braincase.
In human anatomy and development, the facial skeleton is sometimes called the ''membranous visceroc ...
(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 that accommodates the brain. The skull minus the mandible
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the hu ...
that surrounds and houses the brain and
brainstem. The upper areas of the
cranial bones form the
calvaria (skullcap). The membranous viscerocranium includes the
mandible
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...
.
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, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...
, all of the bones of the skull are joined by
sutures—
synarthrodial (immovable)
joints formed by bony
ossification
Ossification (also called osteogenesis or bone mineralization) in bone remodeling is the process of laying down new bone material by cells named osteoblasts. It is synonymous with bone tissue formation. There are two processes resulting in ...
, with
Sharpey's fibres 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.
The human skull is generally considered to consist of twenty-two
bone
A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...
s—eight cranial bones and fourteen facial skeleton bones. In the neurocranium these are the
occipital bone, two
temporal bones, two
parietal bone
The parietal bones () are two bones in the skull which, when joined at a fibrous joint, form the sides and roof of the cranium. In humans, each bone is roughly quadrilateral in form, and has two surfaces, four borders, and four angles. It is n ...
s, the
sphenoid,
ethmoid and
frontal bone
The frontal bone is a bone in the human skull. The bone consists of two portions.'' Gray's Anatomy'' (1918) These are the vertically oriented squamous part, and the horizontally oriented orbital part, making up the bony part of the forehead, ...
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 remainder of the skull is the braincase.
In human anatomy and development, the facial skeleton is sometimes called the ''membranous visceroc ...
(14) are the
vomer
The vomer (; lat, vomer, lit=ploughshare) is one of the unpaired facial bones of the skull. It is located in the midsagittal line, and articulates with the sphenoid, the ethmoid, the left and right palatine bones, and the left and right max ...
, two
inferior nasal conchae, two
nasal bone
The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face and by their junction, form the bridge of the upper one third of the nose.
Ea ...
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. T ...
, the
mandible
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...
, two
palatine bone
In anatomy, the palatine bones () are two irregular bones of the facial skeleton in many animal species, located above the uvula in the throat. Together with the maxillae, they comprise the hard palate. (''Palate'' is derived from the Latin ...
s, two
zygomatic bones, and two
lacrimal bones. 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-shaped bone situated in the anterior midline of the neck between the chin and the thyroid cartilage. At rest, it lies between the base of the mandible and the third cervical verteb ...
or the three
ossicles of the
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 bones.
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 maxillary sinuses are located under the eyes; the frontal sinuses are above the eyes; the ethmoidal sinuses are between the eyes and the spheno ...
, air-filled cavities known as
paranasal sinuses
Paranasal sinuses are a group of four paired air-filled spaces that surround the nasal cavity. The maxillary sinuses are located under the eyes; the frontal sinuses are above the eyes; the ethmoidal sinuses are between the eyes and the sph ...
, and numerous
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 nasal cavity is a large, air-filled space above and behind the nose in the middle of the face. The nasal septum divides the cavity into two cavities, also known as fossae. Each cavity is the continuation of one of the two nostrils. The nasal ...
.
The foramina are openings in the skull. The largest of these is the
foramen magnum 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 (backbone). The backbone encloses the central canal of the sp ...
as well as
nerves and
blood vessel
The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide awa ...
s.
Processes
The many
processes
A process is a series or set of 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 produce a specific se ...
of the skull include the
mastoid process
The mastoid part of the temporal bone is the posterior (back) part of the temporal bone, one of the bones of the skull. Its rough surface gives attachment to various muscles (via tendons) and it has openings for blood vessels. From its borde ...
and the
zygomatic processes.
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 biological sciences. It is the Latin word for "window", and is used in various fields to describe a pore in an anatomical st ...
are anatomical features of the skulls of several types of
amniotes, characterised by bilaterally symmetrical holes (fenestrae) in the temporal bone. Depending on the lineage of a given animal, two, one, or no pairs of temporal fenestrae may be present, above or below the
postorbital and
squamosal bones. The upper temporal fenestrae are also known as the supratemporal fenestrae, and the lower temporal fenestrae are also known as the
infratemporal fenestrae. The presence and morphology of the temporal fenestra 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
synapsids (mammal-like reptiles) and the
diapsids (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. Thus most mammals also have this. Later, primates separated their orbit from ''
temporal fossa'' by the
postorbital bar with
haplorhines
Haplorhini (), the haplorhines ( Greek for "simple-nosed") or the "dry-nosed" primates, is a suborder of primates containing the tarsiers and the simians (Simiiformes or anthropoids), as sister of the Strepsirrhini ("moist-nosed"). The name is ...
later evolving the
postorbital septum
The ''postorbital'' is one of the bones in vertebrate skulls which forms a portion of the dermal skull roof and, sometimes, a ring about the orbit. Generally, it is located behind the postfrontal and posteriorly to the orbital fenestra. In some ve ...
.
=Classification
=
There are four types of amniote skull, classified by the number and location of their temporal fenestrae. These are:
*
Anapsida – no openings
*
Synapsida – one low opening (beneath the postorbital and squamosal bones)
*
Euryapsida – one high opening (above the postorbital and squamosal bones); euryapsids actually evolved from a diapsid configuration, losing their lower temporal fenestra.
*
Diapsida – two openings
Evolutionarily, they are related as follows:
*
Amniota
**Class
Synapsida
***Order
Therapsida
****Class
Mammalia
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur ...
– mammals
**(Unranked)
Sauropsida – reptiles and birds
***Class
Reptilia
****Subclass
Parareptilia
*****Infraclass
Anapsida
****Subclass
Eureptilia
*****Infraclass
Diapsida
******Class
Aves
*****Infraclass
Euryapsida
Bones
The
jugal is a skull bone found in most reptiles, amphibians, and birds. In mammals, the jugal is often called the
zygomatic bone or malar bone.
The
prefrontal bone
The prefrontal bone is a bone separating the lacrimal and frontal bones in many tetrapod skulls. It first evolved in the sarcopterygian clade Rhipidistia, which includes lungfish and the Tetrapodomorpha. The prefrontal is found in most mo ...
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.
Lampreys and sharks only possess a cartilaginous endocranium, with both the upper and lower
jaws being separate elements. Bony fishes have additional
dermal bone, forming a more or less coherent
skull roof
The skull roof, or the roofing bones of the skull, are a set of bones covering the brain, eyes and nostrils in bony fishes and all land-living vertebrates. The bones are derived from dermal bone and are part of the dermatocranium.
In compar ...
in
lungfish
Lungfish are freshwater vertebrates belonging to the order Dipnoi. Lungfish are best known for retaining ancestral characteristics within the Osteichthyes, including the ability to breathe air, and ancestral structures within Sarcopterygii, i ...
and
holost
Holostei is a group of ray-finned bony fish. It is divided into two major clades, the Halecomorphi, represented by a single living species, the bowfin (''Amia calva''), as well as the Ginglymodi, the sole living representatives being the gars (L ...
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
Chondrichthyes (; ) is a class that contains the cartilaginous fishes that have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or ''bony fishes'', which have skeletons primarily composed of bone tissue. ...
, such as
shark
Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachi ...
s 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, and capsules to enclose the
olfactory
The sense of smell, or olfaction, is the special sense through which smells (or odors) are perceived. The sense of smell has many functions, including detecting desirable foods, hazards, and pheromones, and plays a role in taste.
In humans, ...
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, articulating with the first
vertebra. There are, in addition, at various points throughout the cranium, smaller
foramina for the cranial nerves. The jaws consist of separate hoops of cartilage, almost always distinct from the cranium proper.
In
ray-finned fish
Actinopterygii (; ), members of which are known as ray-finned fishes, is a class of bony fish. They comprise over 50% of living vertebrate species.
The ray-finned fishes are so called because their fins are webs of skin supported by bony or h ...
, 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
The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has ...
, 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. T ...
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 vertebrates belonging to the order Dipnoi. Lungfish are best known for retaining ancestral characteristics within the Osteichthyes, including the ability to breathe air, and ancestral structures within Sarcopterygii, i ...
es. The
skull roof
The skull roof, or the roofing bones of the skull, are a set of bones covering the brain, eyes and nostrils in bony fishes and all land-living vertebrates. The bones are derived from dermal bone and are part of the dermatocranium.
In compar ...
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
pterygoids and
vomer
The vomer (; lat, vomer, lit=ploughshare) is one of the unpaired facial bones of the skull. It is located in the midsagittal line, and articulates with the sphenoid, the ethmoid, the left and right palatine bones, and the left and right max ...
s alone, all of which bear teeth. Much of the skull is formed from
cartilage
Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck ...
, and its overall structure is reduced.
Tetrapods
The skulls of the earliest
tetrapod
Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids ( pelycosaurs, extinct t ...
s closely resembled those of their
ancestors amongst the
lobe-finned fishes. The
skull roof
The skull roof, or the roofing bones of the skull, are a set of bones covering the brain, eyes and nostrils in bony fishes and all land-living vertebrates. The bones are derived from dermal bone and are part of the dermatocranium.
In compar ...
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. T ...
,
frontals,
parietals, and
lacrimals, among others. It is overlaying the
endocranium, corresponding to the cartilaginous skull in
sharks and
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
The vomer (; lat, vomer, lit=ploughshare) is one of the unpaired facial bones of the skull. It is located in the midsagittal line, and articulates with the sphenoid, the ethmoid, the left and right palatine bones, and the left and right max ...
and
palatine bone
In anatomy, the palatine bones () are two irregular bones of the facial skeleton in many animal species, located above the uvula in the throat. Together with the maxillae, they comprise the hard palate. (''Palate'' is derived from the Latin ...
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
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
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...
.
In living tetrapods, a great many of the original bones have either disappeared or fused into one another in various arrangements.
Birds
Bird
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...
s have a
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 and
endochondral ossification. The
skull roof
The skull roof, or the roofing bones of the skull, are a set of bones covering the brain, eyes and nostrils in bony fishes and all land-living vertebrates. The bones are derived from dermal bone and are part of the dermatocranium.
In compar ...
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 remainder of the skull is the braincase.
In human anatomy and development, the facial skeleton is sometimes called the ''membranous visceroc ...
and the sides and roof of the neurocranium, are
dermal bones formed by intramembranous ossification, though the
temporal bones are formed by endochondral ossification. The
endocranium, the bones supporting the brain (the
occipital,
sphenoid, and
ethmoid) are largely formed by endochondral ossification. Thus frontal and parietal bones are purely membranous. The geometry of the
skull base and its
fossae, the
anterior,
middle and
posterior cranial fossae changes rapidly. The anterior cranial fossa changes especially during the
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 in the human skull. The bone consists of two portions.'' Gray's Anatomy'' (1918) These are the vertically oriented squamous part, and the horizontally oriented orbital part, making up the bony part of the forehead, ...
). The bones of the
roof of the skull are initially separated by regions of dense
connective tissue
Connective tissue is one of the four primary types of animal tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesenchyme derived from the mesoderm the middle embryonic germ layer. Connective tiss ...
called
fontanelles
A fontanelle (or fontanel) (colloquially, soft spot) is an anatomical feature of the infant human skull comprising soft membranous gaps ( sutures) between the cranial bones that make up the calvaria of a fetus or an infant. Fontanelles allow f ...
. 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
squamous and
lateral parts of the
occipital bone meet. A possible complication of this tension is rupture of the
great cerebral vein
The great cerebral vein is one of the large blood vessels in the skull draining the cerebrum of the brain. It is also known as the "vein of Galen", named for its discoverer, the Greek physician Galen. However, it is not the only vein with this epon ...
. As growth and ossification progress, the connective tissue of the fontanelles is invaded and replaced by bone creating
suture
Suture, literally meaning "seam", may refer to:
Arts, entertainment, and media
* ''Suture'' (album), a 2000 album by American Industrial rock band Chemlab
* ''Suture'' (film), a 1993 film directed by Scott McGehee and David Siegel
* Suture (ban ...
s. The five sutures are the two
squamous sutures, one
coronal, one
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
Craniosynostosis is a condition in which one or more of the fibrous sutures in a young infant's skull prematurely fuses by turning into bone (ossification), thereby changing the growth pattern of the skull. Because the skull cannot expand perpe ...
is a condition in which one or more of the fibrous
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
Intracranial pressure (ICP) is the pressure exerted by fluids such as cerebrospinal fluid (CSF) inside the skull and on the brain tissue. ICP is measured in millimeters of mercury ( mmHg) and at rest, is normally 7–15 mmHg for a supine adul ...
leading possibly to visual impairment, sleeping impairment, eating difficulties, or an impairment of mental development.
A
copper beaten skull Copper beaten skull is a phenomenon wherein intense intracranial pressure disfigures the internal surface of the skull.http://radiopaedia.org/articles/copper-beaten-skull The name comes from the fact that the inner skull has the appearance of havi ...
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
A ball-peen or ball pein hammer, also known as a machinist's hammer, is a type of peening hammer used in metalworking. It has two heads, one flat and the other, called the peen, rounded. It is distinguished from a cross-peen hammer, diagonal-peen ...
, 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
Intracranial pressure (ICP) is the pressure exerted by fluids such as cerebrospinal fluid (CSF) inside the skull and on the brain tissue. ICP is measured in millimeters of mercury ( mmHg) and at rest, is normally 7–15 mmHg for a supine adul ...
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.
Dating back to
Neolithic
The Neolithic period, or New Stone Age, is an Old World archaeological period and the final division of the Stone Age. It saw the Neolithic Revolution, a wide-ranging set of developments that appear to have arisen independently in several pa ...
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
Decompressive craniectomy ('' crani-'' + '' -ectomy'') is a neurosurgical procedure in which part of the skull is removed to allow a swelling brain room to expand without being squeezed. It is performed on victims of traumatic brain injury, ...
.
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-printed polymer
A polymer (; Greek '' poly-'', "many" + '' -mer'', "part")
is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...
implant
Implant can refer to:
Medicine
* Implant (medicine), or specifically:
**Brain implant
**Breast implant
** Buttock implant
**Cochlear implant
**Contraceptive implant
**Dental implant
** Fetal tissue implant
** Implantable cardioverter-defibrillato ...
. 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
Harvard Medical School (HMS) is the graduate medical school of Harvard University and is located in the Longwood Medical Area of Boston, Massachusetts. Founded in 1782, HMS is one of the oldest medical schools in the United States and is cons ...
in Boston, funded by
National Institutes of Health
The National Institutes of Health, commonly referred to as NIH (with each letter pronounced individually), is the primary agency of the United States government responsible for biomedical and public health research. It was founded in the lat ...
(NIH), suggested that instead of travelling via
blood
Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the cir ...
, there are "tiny channels" in the skull through which the
immune cells
White blood cells, also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and derived from mul ...
combined with the
bone marrow reach the areas of
inflammation
Inflammation (from la, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants, and is a protective response involving immune cells, blood vessels, and molec ...
after an injury to the brain tissues.
Transgender procedures
Surgical alteration of
sexually dimorphic skull features may be carried out as a part of
facial feminization surgery
Facial feminization surgery (FFS) is a set of reconstructive surgical procedures that alter typically male facial features to bring them closer in shape and size to typical female facial features. FFS can include various bony and soft tissue proced ...
, 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.
Forensic scientists and
archaeologist
Archaeology or archeology is the scientific study of human activity through the recovery and analysis of material culture. The archaeological record consists of artifacts, architecture, biofacts or ecofacts, sites, and cultural landsca ...
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 mounds in Japan,
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
Franz Josef Gall (; 9 March 175822 August 1828) was a German neuroanatomist, physiologist, and pioneer in the study of the localization of mental functions in the brain.
Claimed as the founder of the pseudoscience of phrenology, Gall was an ...
in around 1800 formulated the theory of
phrenology
Phrenology () is a pseudoscience which involves the measurement of bumps on the skull to predict mental traits.Wihe, J. V. (2002). "Science and Pseudoscience: A Primer in Critical Thinking." In ''Encyclopedia of Pseudoscience'', pp. 195–203. C ...
, 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
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
James McGrigor Allan (1827, Bristol - 1916, Epsom) was a British anthropologist and writer.
Biography
McGrigor was the son of Colin Allan, at one time chief medical officer of Halifax, Nova Scotia
Halifax is the capital and largest municipal ...
, 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's 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 ridge
The brow ridge, or supraorbital ridge known as superciliary arch in medicine, is a bony ridge located above the eye sockets of all primates. In humans, the eyebrows are located on their lower margin.
Structure
The brow ridge is a nodule or cre ...
s, a more prominent
glabella
The glabella, in humans, is the area of skin between the eyebrows and above the nose. The term also refers to the underlying bone that is slightly depressed, and joins the two brow ridges. It is a cephalometric landmark that is just superior t ...
, and more prominent
temporal lines. Female skulls generally have rounder
orbit
In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as ...
s, and narrower jaws. Male skulls on average have larger, broader
palates, squarer orbits, larger
mastoid process
The mastoid part of the temporal bone is the posterior (back) part of the temporal bone, one of the bones of the skull. Its rough surface gives attachment to various muscles (via tendons) and it has openings for blood vessels. From its borde ...
es, larger
sinuses, and larger
occipital condyles than those of females. Male
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
The glabella, in humans, is the area of skin between the eyebrows and above the nose. The term also refers to the underlying bone that is slightly depressed, and joins the two brow ridges. It is a cephalometric landmark that is just superior t ...
to the occipital point.
Humans may be:
* ''Dolichocephalic'' — long-headed
* ''Mesaticephalic'' — medium-headed
* ''Brachycephalic'' — short-headed
Terminology
*
Chondrocranium
The chondrocranium (or ''cartilaginous neurocranium'') is the primitive cartilaginous skeletal structure of the fetal skull that grows to envelop the rapidly growing embryonic brain.Salentijn, L. ''Biology of Mineralized Tissues: Prenatal Skull De ...
, a primitive cartilaginous skeletal structure
*
Endocranium
*
Epicranium
The Epicranium is the medical term for the collection of structures covering the cranium. It consists of the muscles, aponeurosis
An aponeurosis (; plural: ''aponeuroses'') is a type or a variant of the deep fascia, in the form of a sheet of pe ...
*
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
Archaeology or archeology is the scientific study of human activity through the recovery and analysis of material culture. The archaeological record consists of artifacts, architecture, biofacts or ecofacts, sites, and cultural landscap ...
evidence,
found in the forms of cave paintings and human remains. At one burial site in
France
France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...
dated to 6500 BCE, 40 out of 120
prehistoric skulls found had trepanation holes.
Additional images
See also
*
Craniometry
*
Crystal skull
*
Head and neck anatomy
*
Human skull symbolism
Skull symbolism is the attachment of symbolic meaning to the human skull. The most common symbolic use of the skull is as a representation of death, mortality and the unachievable nature of immortality.
Humans can often recognize the buried fragm ...
*
Memento mori
*
Plagiocephaly, the abnormal flattening of one side of the skull
*
Skull and crossbones (disambiguation)
*
Teshik-Tash
Teshik-Tash 1 is a Neanderthal skeleton discovered in 1938 in Teshik-Tash Cave, in the Bajsuntau mountain range, Uzbek SSR, Central Asia.
The remains were discovered in 1938 by A. P. Okladnikov. They were found in a shallow pit, reported to be ...
*
Totenkopf
''Totenkopf'' (, i.e. ''skull'', literally "dead person's head") is the German word for the skull and crossbones symbol. The "skull and crossbones" symbol is an old international symbol for death, the defiance of death, danger, or the dead, as ...
*
Yorick
*
Overmodelled skull
An overmodelled skull is a skull covered with various materials to reconstruct the appearance of a human head. This technique of art and religion is described in many countries throughout the ages.
Origins
A custom that has existed since the Neo ...
*
Diploë
References
External links
Skull Module(
California State University Department of Anthology)
Skull Anatomy Tutorial.(
GateWay Community College)
Bird Skull CollectionBird 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
Vertebrate anatomy
Flat bones
Bones of the head and neck
Human head and neck