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The skull, or cranium, is typically a Bone enclosure around the brain of a vertebrate. In some fish, and , the skull is of cartilage. The skull is at the head end of the vertebrate.
In the human, the skull comprises two prominent parts: the neurocranium and the facial skeleton, which evolution from the first pharyngeal arch. The skull forms the frontmost portion of the axial skeleton and is a product of cephalization and brain vesicle of the brain, with several special senses structures such as the , , nose, tongue and, in fish, specialized touch organs such as barbels near the mouth.
The skull is composed of three types of bone: cranial bones, and , which is made up of a number of fused flat bone and . The cranial bones are joined at firm fibrous junctions called sutures and contains many foramina, fossae, processes, and sinuses. In zoology, the openings in the skull are called , the most prominent of which is the foramen magnum, where the brainstem goes through to join the spinal cord.
In human anatomy, the neurocranium (or braincase), is further divided into the calvarium and the endocranium, together forming a cranial cavity that houses the brain. The interior periosteum forms part of the dura mater, the facial skeleton and splanchnocranium with the mandible being its largest bone. The mandible joint with the of the neurocranium at the paired temporomandibular joints. The skull itself articulates with the spinal column at the atlanto-occipital joint. The human skull fully develops two years after birth.
Functions of the skull include physical protection for the brain, providing attachments for neck , facial muscles and muscles of mastication, providing fixed and ( and auricles) to enable stereoscopic vision and sound localisation, forming nasal cavity and oral cavity that allow better olfaction, taste and digestion, and contributing to phonation by acoustic resonance within the cavities and sinuses. In some animals such as and , the skull also has a function in anti-predator defense and sexual selection by providing the foundation for horns, and .
The English word skull is probably derived from Old Norse skulle, while the Latin word cranium comes from the Greek root κρανίον (kranion).
The skull consists of three parts, of different embryology 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. The upper areas of the neurocranium form the calvaria (skullcap). The facial skeleton (membranous viscerocranium) is formed by the bones supporting the face, and includes the mandible.
The bones of the skull are joined by known as sutures—synarthrodial (immovable) formed by bony ossification, with Sharpey's fibres permitting some flexibility. Sometimes there can be extra bone pieces within the suture known as or sutural bones. Most commonly these are found in the course of the lambdoid suture.
The bones of the facial skeleton (14) are the vomer, two inferior nasal conchae, two , two maxilla, the mandible, two , two , and two . Some sources count a paired bone as one, or the maxilla as having two bones (as its parts); some sources include the hyoid bone or the three ossicles of the middle ear, the malleus, incus, and stapes, but the overall general consensus of the number of bones in the human skull is the stated twenty-two.
Some of these bones—the occipital, parietal, frontal, in the neurocranium, and the nasal, lacrimal, and vomer, in the facial skeleton are .
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 and .
The fenestrae (from Latin, meaning windows) are openings in the skull.
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The prefrontal bone is a bone that separates the lacrimal and frontal bones in many tetrapod skulls.
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, 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. (1977). 003910284X, Holt-Saunders International. 003910284X
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.
Although the skulls of fossil lobe-finned fish resemble those of the early tetrapods, the same cannot be said of those of the living . The skull roof is not fully formed, and consists of multiple, somewhat irregularly shaped bones with no direct relationship to those of tetrapods. The upper jaw is formed from the pterygoid bone and alone, all of which bear teeth. Much of the skull is formed from cartilage, and its overall structure is reduced.
In living tetrapods, a great many of the original bones have either disappeared or fused into one another in various arrangements.
At birth, the human skull is made up of 44 separate bony elements. During development, many of these bony elements gradually fuse together into solid bone (for example, the frontal bone). The bones of the skull roof 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 squamosal suture, one coronal suture, one lambdoid suture, 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. (2025). 9788123923321, CBS Publishers & Distributors. ISBN 9788123923321
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 . The condition is most common in children.
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-printed polymer 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 (NIH), suggested that instead of travelling via blood, there are "tiny channels" in the skull through which the immune cells combined with the bone marrow reach the areas of inflammation after an injury to the brain tissues.
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.
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.Other Sources:
However, other studies shows that men's skulls are slightly thicker in certain areas. Some studies show that females are more susceptible to 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 all have more prominent supraorbital ridges, glabella, and parietal bone. Female skulls generally have rounder orbits and narrower jaws. Male skulls on average have larger, broader , squarer orbits, larger , larger Paranasal sinus, and larger occipital condyles than those of females. Male mandibles typically have squarer chins and thicker, rougher muscle attachments than female mandibles.
Humans may be:
The vertical cephalic index refers to the ratio between the height of the head multiplied by 100 and divided by the length of the head.Humans may be:
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