Humans<unk>  in situ pericranium Human<unk>  from the front Side bones of<unk>  The human<unk>  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<unk> s of other vertebrates, it protects the brain from injury. The<unk>  consists of three parts, of different embryological origin—the neurocranium, the sutures, and the facial skeleton (also called the membraneous viscerocranium). The neurocranium (or braincase) forms the protective cranial cavity that surrounds and houses the brain and brainstem. The upper areas of the cranial bones form the calvaria<unk> cap). 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<unk>  are joined together 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. The human<unk>  is generally considered to consist of twenty-two bones—eight cranial bones and fourteen facial skeleton bones. In the neurocranium these are the occipital bone, two temporal bones, two parietal bones, the sphenoid, ethmoid and frontal bones. The bones of the facial skeleton (14) are the vomer, two inferior nasal conchae, two nasal bones, two maxilla, the mandible, two palatine bones, 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 or the three ossicles of the middle ear but the overall general consensus of the number of bones in the human<unk>  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 CT scan of a human<unk>  in 3D The<unk>  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<unk> , 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<unk> . The largest of these is the foramen magnum that allows the passage of the spinal cord as well as nerves and blood vessels. Processes The many processes of the<unk>  include the mastoid process and the zygomatic processes. Other vertebrates Fenestrae A Centrosaurus<unk>  Scheme of Spinosaurus<unk>  fenestrae in the<unk>  of the dinosaur Massospondylus The fenestrae (from Latin, meaning windows) are openings in the<unk> . * Antorbital fenestra * Mandibular fenestra * Quadratojugal fenestra * Subsquamosal fenestra, an opening between two parts of the squamosal bone in some rodents * Temporal fenestra The temporal fenestrae are anatomical features of the<unk> s 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<unk> , 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 later evolving the postorbital septum. Classification 258x258px Goat<unk> . There are four types of amniote<unk> , 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 *(Unranked) Sauropsida – reptiles and birds *Class Reptilia *Subclass Parareptilia *Infraclass Anapsida *Subclass Eureptilia *Infraclass Diapsida *Class Aves *Infraclass Euryapsida Bones The jugal is a<unk>  bone found in most reptiles, amphibians, and birds. In mammals, the jugal is often called the zygomatic bone or malar bone. The prefrontal bone is a bone separating the lacrimal and frontal bones in many tetrapod<unk> s. Fish Fish head parts, 1889, Fauna of British India, Sir Francis Day<unk>  of a swordfish The<unk>  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<unk>  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. Cartilaginous fish, such as sharks and rays, have also simple, and presumably primitive,<unk>  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<unk>  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, there has also been considerable modification from the primitive pattern. The roof of the<unk>  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<unk> , 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<unk> s of fossil lobe-finned fish resemble those of the early tetrapods, the same cannot be said of those of the living lungfishes. The<unk>  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<unk>  is formed from cartilage, and its overall structure is reduced. Tetrapods<unk>  of Tiktaalik, an extinct genus transitional between lobe-finned fish and early tetrapods The<unk> s of the earliest tetrapods closely resembled those of their ancestors amongst the lobe-finned fishes. The<unk>  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<unk>  in sharks and rays. The various separate bones that compose the temporal bone of humans are also part of the<unk>  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. In living tetrapods, a great many of the original
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