The skull is a
bone protective
cavity for the
brain.[1] The skull is composed of three types of bone: cranial bones, facial bones, and ear ossicles. Two parts are more prominent: the cranium (
pl.: craniums or crania) and the
mandible.[2] In
humans, these two parts are the
neurocranium (braincase) and the viscerocranium (
facial skeleton) that includes the mandible as its largest bone. The skull forms the anterior-most portion of the
skeleton and is a product of
cephalisation—housing the brain, and several
sensory structures such as the eyes, ears, nose, and mouth.[3] 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 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) for the
horns.
The English word skull is probably derived from
Old Norseskulle,[4] while the
Latin word cranium comes from the
Greek rootκρανίον (kranion). The human skull fully develops two years after birth. The junctions of the skull bones are joined by structures called
sutures.
The human skull is the bone structure that forms the
head in the
human skeleton. It supports the structures of the
face and forms a cavity for the
brain. Like the skulls of other vertebrates, it protects the brain from injury.[5]
The skull consists of three parts, of different
embryological origin—the
neurocranium, the sutures, and the facial skeleton. The neurocranium (or braincase) forms the protective
cranial cavity that surrounds and houses the brain and
brainstem.[6] The upper areas of the
cranial bones form the
calvaria (skullcap). The membranous viscerocranium includes the
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, all of the bones of the skull are joined by
sutures—
synarthrodial (immovable)
joints formed by bony
ossification, 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.
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, air-filled cavities known as
paranasal sinuses, 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 foramina are openings in the skull. The largest of these is the
foramen magnum, of the occipital bone, that allows the passage of the
spinal cord as well as
nerves and
blood vessels.
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.[7]
The
prefrontal bone 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 in
lungfish and
holost 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.[8]
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, 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, 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.[8]
In
ray-finned fish, there has also been considerable modification from the primitive pattern. The roof of the skull is generally well formed, and although the exact relationship of its bones to those of tetrapods is unclear, they are usually given similar names for convenience. Other elements of the skull, however, may be reduced; there is little cheek region behind the enlarged orbits, and little, if any bone in between them. The upper jaw is often formed largely from the
premaxilla, with the maxilla itself located further back, and an additional bone, the symplectic, linking the jaw to the rest of the cranium.[9]
Although the skulls of fossil lobe-finned fish resemble those of the early tetrapods, the same cannot be said of those of the living
lungfishes. The
skull roof is not fully formed, and consists of multiple, somewhat irregularly shaped bones with no direct relationship to those of tetrapods. The upper jaw is formed from the
pterygoids and
vomers alone, all of which bear teeth. Much of the skull is formed from
cartilage, and its overall structure is reduced.[9]
Tetrapods
The skulls of the earliest
tetrapods closely resembled those of their
ancestors amongst the
lobe-finned fishes. The
skull roof is formed of a series of plate-like bones, including the maxilla,
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 and
palatine bones. 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.[9]
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 skull, as in reptiles, with a prelacrimal fossa (present in some reptiles). The skull has a single occipital condyle.[10] 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.[9] 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 bones, comprising the bones of the facial skeleton 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.[11] 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.[12]
At birth, the human skull is made up of 44 separate bony elements. During development, many of these bony elements gradually fuse together into solid bone (for example, the
frontal bone). The bones of the
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
squamous and
lateral parts of the occipital bone meet. A possible complication of this tension is rupture of the
great cerebral vein. As growth and ossification progress, the connective tissue of the fontanelles is invaded and replaced by bone creating
sutures. 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.[13]
Clinical significance
Craniosynostosis is a condition in which one or more of the fibrous
sutures in an infant skull prematurely fuses,[14] and changes the growth pattern of the skull.[15] Because the skull cannot expand perpendicular to the fused suture, it grows more in the parallel direction.[15] Sometimes the resulting growth pattern provides the necessary space for the growing brain, but results in an abnormal head shape and abnormal facial features.[15] 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.[16]
A
copper beaten skull is a phenomenon wherein intense intracranial pressure disfigures the internal surface of the skull.[17] 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 high resistance to deformation; the skull is one of the least deformable structures found in nature, needing the force of about 1 ton to reduce its diameter by 1 cm.[18] In some cases of
head injury, however, there can be raised
intracranial pressure through mechanisms such as a
subdural haematoma. In these cases, the raised intracranial pressure can cause herniation of the brain out of the foramen magnum ("coning") because there is no space for the brain to expand; this can result in significant
brain damage or death unless an urgent operation is performed to relieve the pressure. This is why patients with
concussion must be watched extremely carefully. Repeated concussions can activate the structure of skull bones as the brain's protective covering.[19]
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-printedpolymerimplant.[20] 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.[21]
Artificial cranial deformation is a largely historical practice of some cultures. Cords and wooden boards would be used to apply pressure to an infant's skull and alter its shape, sometimes quite significantly. This procedure would begin just after birth and would be carried on for several years.[citation needed]
Osteology
Like the face, the skull and teeth can also indicate a person's life history and origin.
Forensic scientists and
archaeologists 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
Jōmonshell 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.[citation needed]
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
pseudoscientific.[citation needed]
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.[27] 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.[27] 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.[27]
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.[28] However, later studies show that women's skulls are slightly thicker and thus men may be more susceptible to head injury than women.[29] However, other studies shows that men's skulls are slightly thicker in certain areas.[30] As well as some studies showing that females are more susceptible to head injury (concussion) than males.[31] 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.[32][33]
Male skulls can all have more prominent
supraorbital ridges,
glabella, and
temporal lines. Female skulls generally have rounder
orbits and narrower jaws. Male skulls on average have larger, broader
palates, squarer orbits, larger
mastoid processes, larger
sinuses, and larger
occipital condyles than those of females. Male mandibles typically have squarer chins and thicker, rougher muscle attachments than female mandibles.[34]
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.
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,[35] 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 skulls found had trepanation holes.[36]
^Dechow, Paul C.; Wang, Qian (January 2017). "Evolution of the Jugal/Zygomatic Bones". The Anatomical Record. 300 (1): 12–15.
doi:
10.1002/ar.23519.
^
abRomer, Alfred Sherwood; Thomas S., Parsons (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 173–177.
ISBN0-03-910284-X.
^
abcdRomer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 216–247.
ISBN0-03-910284-X.
^Wing, Leonard W. (1956). "The Place of Birds in Nature".
Natural History of Birds. The Ronald Press Company. pp.
22–23.
^Carlson, Bruce M. (1999). Human Embryology & Developmental Biology (Second ed.). Mosby. pp. 166–170.
ISBN0-8151-1458-3.
^
abChaurasia, B. D. (2013). BD Chaurasia's Human Anatomy: Regional and Applied Dissection and Clinical. Vol. 3: Head–Neck Brain (Sixth ed.). CBS Publishers & Distributors. pp. 29–30.
ISBN978-81-239-2332-1.
Li, Haiyan; Ruan, Jesse; Xie, Zhonghua; Wang, Hao; Liu, Wengling (2007). "Investigation of the critical geometric characteristics of living human skulls utilising medical image analysis techniques". International Journal of Vehicle Safety. 2 (4): 345.
doi:
10.1504/IJVS.2007.016747.
Adeloye, Adelola; Kattan, Kenneth R.; Silverman, Frederic N. (July 1975). "Thickness of the normal skull in the American blacks and whites". American Journal of Physical Anthropology. 43 (1): 23–30.
doi:
10.1002/ajpa.1330430105.
PMID1155589.
^Schulte-Geers, Christina; Obert, Martin; Schilling, René L.; Harth, Sebastian; Traupe, Horst; Gizewski, Elke R.; Verhoff, Marcel A. (2011). "Age and gender-dependent bone density changes of the human skull disclosed by high-resolution flat-panel computed tomography". International Journal of Legal Medicine. 125 (3): 417–425.
doi:
10.1007/s00414-010-0544-3.
PMID21234583.
S2CID39294670.
^Capasso, Luigi (2002). Principi di storia della patologia umana: corso di storia della medicina per gli studenti della Facoltà di medicina e chirurgia e della Facoltà di scienze infermieristiche (in Italian). Rome: SEU.
ISBN978-88-87753-65-3.
OCLC50485765.
^Restak, Richard (2000). "Fixing the Brain". Mysteries of the Mind. Washington, D.C.: National Geographic Society.
ISBN978-0-7922-7941-9.
OCLC43662032.
The skull is a
bone protective
cavity for the
brain.[1] The skull is composed of three types of bone: cranial bones, facial bones, and ear ossicles. Two parts are more prominent: the cranium (
pl.: craniums or crania) and the
mandible.[2] In
humans, these two parts are the
neurocranium (braincase) and the viscerocranium (
facial skeleton) that includes the mandible as its largest bone. The skull forms the anterior-most portion of the
skeleton and is a product of
cephalisation—housing the brain, and several
sensory structures such as the eyes, ears, nose, and mouth.[3] 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 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) for the
horns.
The English word skull is probably derived from
Old Norseskulle,[4] while the
Latin word cranium comes from the
Greek rootκρανίον (kranion). The human skull fully develops two years after birth. The junctions of the skull bones are joined by structures called
sutures.
The human skull is the bone structure that forms the
head in the
human skeleton. It supports the structures of the
face and forms a cavity for the
brain. Like the skulls of other vertebrates, it protects the brain from injury.[5]
The skull consists of three parts, of different
embryological origin—the
neurocranium, the sutures, and the facial skeleton. The neurocranium (or braincase) forms the protective
cranial cavity that surrounds and houses the brain and
brainstem.[6] The upper areas of the
cranial bones form the
calvaria (skullcap). The membranous viscerocranium includes the
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, all of the bones of the skull are joined by
sutures—
synarthrodial (immovable)
joints formed by bony
ossification, 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.
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, air-filled cavities known as
paranasal sinuses, 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 foramina are openings in the skull. The largest of these is the
foramen magnum, of the occipital bone, that allows the passage of the
spinal cord as well as
nerves and
blood vessels.
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.[7]
The
prefrontal bone 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 in
lungfish and
holost 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.[8]
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, 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, 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.[8]
In
ray-finned fish, there has also been considerable modification from the primitive pattern. The roof of the skull is generally well formed, and although the exact relationship of its bones to those of tetrapods is unclear, they are usually given similar names for convenience. Other elements of the skull, however, may be reduced; there is little cheek region behind the enlarged orbits, and little, if any bone in between them. The upper jaw is often formed largely from the
premaxilla, with the maxilla itself located further back, and an additional bone, the symplectic, linking the jaw to the rest of the cranium.[9]
Although the skulls of fossil lobe-finned fish resemble those of the early tetrapods, the same cannot be said of those of the living
lungfishes. The
skull roof is not fully formed, and consists of multiple, somewhat irregularly shaped bones with no direct relationship to those of tetrapods. The upper jaw is formed from the
pterygoids and
vomers alone, all of which bear teeth. Much of the skull is formed from
cartilage, and its overall structure is reduced.[9]
Tetrapods
The skulls of the earliest
tetrapods closely resembled those of their
ancestors amongst the
lobe-finned fishes. The
skull roof is formed of a series of plate-like bones, including the maxilla,
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 and
palatine bones. 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.[9]
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 skull, as in reptiles, with a prelacrimal fossa (present in some reptiles). The skull has a single occipital condyle.[10] 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.[9] 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 bones, comprising the bones of the facial skeleton 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.[11] 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.[12]
At birth, the human skull is made up of 44 separate bony elements. During development, many of these bony elements gradually fuse together into solid bone (for example, the
frontal bone). The bones of the
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
squamous and
lateral parts of the occipital bone meet. A possible complication of this tension is rupture of the
great cerebral vein. As growth and ossification progress, the connective tissue of the fontanelles is invaded and replaced by bone creating
sutures. 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.[13]
Clinical significance
Craniosynostosis is a condition in which one or more of the fibrous
sutures in an infant skull prematurely fuses,[14] and changes the growth pattern of the skull.[15] Because the skull cannot expand perpendicular to the fused suture, it grows more in the parallel direction.[15] Sometimes the resulting growth pattern provides the necessary space for the growing brain, but results in an abnormal head shape and abnormal facial features.[15] 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.[16]
A
copper beaten skull is a phenomenon wherein intense intracranial pressure disfigures the internal surface of the skull.[17] 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 high resistance to deformation; the skull is one of the least deformable structures found in nature, needing the force of about 1 ton to reduce its diameter by 1 cm.[18] In some cases of
head injury, however, there can be raised
intracranial pressure through mechanisms such as a
subdural haematoma. In these cases, the raised intracranial pressure can cause herniation of the brain out of the foramen magnum ("coning") because there is no space for the brain to expand; this can result in significant
brain damage or death unless an urgent operation is performed to relieve the pressure. This is why patients with
concussion must be watched extremely carefully. Repeated concussions can activate the structure of skull bones as the brain's protective covering.[19]
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-printedpolymerimplant.[20] 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.[21]
Artificial cranial deformation is a largely historical practice of some cultures. Cords and wooden boards would be used to apply pressure to an infant's skull and alter its shape, sometimes quite significantly. This procedure would begin just after birth and would be carried on for several years.[citation needed]
Osteology
Like the face, the skull and teeth can also indicate a person's life history and origin.
Forensic scientists and
archaeologists 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
Jōmonshell 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.[citation needed]
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
pseudoscientific.[citation needed]
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.[27] 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.[27] 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.[27]
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.[28] However, later studies show that women's skulls are slightly thicker and thus men may be more susceptible to head injury than women.[29] However, other studies shows that men's skulls are slightly thicker in certain areas.[30] As well as some studies showing that females are more susceptible to head injury (concussion) than males.[31] 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.[32][33]
Male skulls can all have more prominent
supraorbital ridges,
glabella, and
temporal lines. Female skulls generally have rounder
orbits and narrower jaws. Male skulls on average have larger, broader
palates, squarer orbits, larger
mastoid processes, larger
sinuses, and larger
occipital condyles than those of females. Male mandibles typically have squarer chins and thicker, rougher muscle attachments than female mandibles.[34]
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.
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,[35] 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 skulls found had trepanation holes.[36]
^Dechow, Paul C.; Wang, Qian (January 2017). "Evolution of the Jugal/Zygomatic Bones". The Anatomical Record. 300 (1): 12–15.
doi:
10.1002/ar.23519.
^
abRomer, Alfred Sherwood; Thomas S., Parsons (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 173–177.
ISBN0-03-910284-X.
^
abcdRomer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 216–247.
ISBN0-03-910284-X.
^Wing, Leonard W. (1956). "The Place of Birds in Nature".
Natural History of Birds. The Ronald Press Company. pp.
22–23.
^Carlson, Bruce M. (1999). Human Embryology & Developmental Biology (Second ed.). Mosby. pp. 166–170.
ISBN0-8151-1458-3.
^
abChaurasia, B. D. (2013). BD Chaurasia's Human Anatomy: Regional and Applied Dissection and Clinical. Vol. 3: Head–Neck Brain (Sixth ed.). CBS Publishers & Distributors. pp. 29–30.
ISBN978-81-239-2332-1.
Li, Haiyan; Ruan, Jesse; Xie, Zhonghua; Wang, Hao; Liu, Wengling (2007). "Investigation of the critical geometric characteristics of living human skulls utilising medical image analysis techniques". International Journal of Vehicle Safety. 2 (4): 345.
doi:
10.1504/IJVS.2007.016747.
Adeloye, Adelola; Kattan, Kenneth R.; Silverman, Frederic N. (July 1975). "Thickness of the normal skull in the American blacks and whites". American Journal of Physical Anthropology. 43 (1): 23–30.
doi:
10.1002/ajpa.1330430105.
PMID1155589.
^Schulte-Geers, Christina; Obert, Martin; Schilling, René L.; Harth, Sebastian; Traupe, Horst; Gizewski, Elke R.; Verhoff, Marcel A. (2011). "Age and gender-dependent bone density changes of the human skull disclosed by high-resolution flat-panel computed tomography". International Journal of Legal Medicine. 125 (3): 417–425.
doi:
10.1007/s00414-010-0544-3.
PMID21234583.
S2CID39294670.
^Capasso, Luigi (2002). Principi di storia della patologia umana: corso di storia della medicina per gli studenti della Facoltà di medicina e chirurgia e della Facoltà di scienze infermieristiche (in Italian). Rome: SEU.
ISBN978-88-87753-65-3.
OCLC50485765.
^Restak, Richard (2000). "Fixing the Brain". Mysteries of the Mind. Washington, D.C.: National Geographic Society.
ISBN978-0-7922-7941-9.
OCLC43662032.