Skull

For other uses of "Skull", see Skull (disambiguation).

"Cranium" redirects here. For other uses, see Cranium (disambiguation).

A closeup of the front of a damaged human skull.

The skull is a bony structure found in the head of many animals. Bones are rigid organs that form part of the Endoskeleton of Vertebrates They function to move support and protect the various organs of the body produce The skull supports the structures of the face and protects the head against injury. The term face refers to the central sense organ complex for those animals that have one normally on the ventral surface of the head and can depending on the definition In Anatomy, the head of an Animal is the Rostral part (from Anatomical position that usually comprises the Brain, Eyes

The skull can be subdivided into two parts: the cranium and the mandible. A skull that is missing a mandible is only a cranium; this is the source of a very commonly made error in terminology. Those animals having skulls are called craniates. For the class of Brachiopods see Craniforma. Craniata (sometimes Craniota) is a proposed Clade of

Protection of the brain is only one part of the function of a bony skull. For example, a fixed distance between the eyes is essential for stereoscopic vision, and a fixed position for the ears helps the brain to use auditory cues to judge direction and distance of sounds. Stereopsis (from stereo meaning solidity and opsis meaning vision or Sight) is the process in Visual perception leading to the sensation In some animals, the skull also has a defensive function (e. g. horned ungulates); the frontal bone is where horns are mounted. Ungulates (meaning roughly "being Hoofed quot or "hoofed animal" are several groups of Mammals most of which use the tips of their toes usually The frontal bone is a Bone in the Human Skull that resembles a cockleshell in form and consists of two portions a vertical

1 Human skulls
2 Possible types of skull fractures
3 Other skulls
- 3.1 Temporal Fenestra
  - 3.1.1 Classification
4 See also
5 References
6 External links

Human skulls

Main article: Human skull

Human skull (front)

Human skull (side)

In humans, the adult skull is normally made up of 22 bones. In humans the adult skull is normally made up of 22 bones Except for the Mandible, all of the bones of the Skull are joined together by sutures, Bones are rigid organs that form part of the Endoskeleton of Vertebrates They function to move support and protect the various organs of the body produce Except for the mandible, all of the bones of the skull are joined together by sutures, rigid articulations permitting very little movement. The mandible (from Latin mandibula, "jawbone" or inferior maxillary bone forms the lower Jaw and holds the lower teeth in place This article is about joints in the bones of the cranium There is also an article about sutures as features of a wide range of animals. Eight bones form the neurocranium (braincase)—including the frontal, parietals, occipital bone, sphenoid, temporals and ethmoid—a protective vault surrounding the brain. The occipital bone, a saucer-shaped membrane bone situated at the back and lower part of the cranium, is trapezoid in shape and curved on itself The sphenoid bone (from Greek sphenoeides, "wedgelike" is a Bone situated at the base of the Skull in front of the Temporals and basilar The ethmoid bone (from Greek ethmos, "sieve" is a Bone in the Skull that separates the Nasal cavity from the Brain. The cranial vault is the space in the Skull within the neurocranium. Fourteen bones form the splanchnocranium, the bones supporting the face. Encased within the temporal bones are the six ear ossicles of the middle ears, though these are not part of the skull. The temporal bones are situated at the sides and base of the Skull. The ossicles (also called auditory ossicles) are the three smallest Bones in the human body The middle ear is the portion of the ear internal to the Eardrum, and external to the Oval window of the Cochlea. The hyoid bone, supporting the tongue, is usually not considered as part of the skull either, as it does not articulate with any other bones. The hyoid bone ( lingual bone) (Latin os hyoideum) is a Bone in the Neck, and is the only bone in the human skeleton not articulated to any The tongue is the large bundle of Skeletal muscles on the floor of the Mouth that manipulates Food for chewing and swallowing (deglutition The skull is a protector of the brain.

The skull contains the sinus cavities, which are air-filled cavities lined with respiratory epithelium, which also lines the large airways. Paranasal sinuses are air-filled spaces communicating with the nasal cavity within the bones of the Skull and face Respiratory Epithelium is a type of Epithelium found lining the Respiratory tract, where it serves to moisten and protect the airways The exact functions of the sinuses are unclear; they may contribute to decreasing the weight of the skull with a minimal decrease in strength,or they may be important in improving the resonance of the voice. In some animals, such as the elephant, the sinuses are extensive. Elephants ( family: Elephantidae) are large land Mammals of the order Proboscidea. The elephant skull needs to be very large, to form an attachment for muscles of the neck and trunk, but is also unexpectedly light; the comparatively small brain-case is surrounded by large sinuses which reduce the weight.

The meninges are the three layers, or membranes, which surround the structures of the nervous system. The meninges (singular meninx) is the system of membranes which envelops the Central nervous system. The nervous system is a Network of specialized cells that communicate information about an animal's surroundings and itself They are known as the dura mater, the arachnoid mater and the pia mater. The dura mater (from the Latin "hard mother" or pachymeninx, is the tough and inflexible outermost of the three layers of the Meninges surrounding the The arachnoid mater is one of the three Meninges, the membranes that cover the Brain and Spinal cord. The pia mater (Latin "tender mother" itself a translation from Arabic) is the delicate innermost layer of the Meninges - the membranes surrounding the Other than being classified together, they have little in common with each other.

In humans, the anatomical position for the skull is the Frankfurt plane, where the lower margins of the orbits and the upper borders of the ear canals are all in a horizontal plane. In fields of Anatomy, anatomical terms of location are descriptive terms to help identify relative positions or directions within a species The Frankfurt plane (also called the auriculo-orbital plane) was established at the World Congress on Anthropology in Frankfurt, Germany in In Anatomy, the orbital bone is the cavity or socket of the Skull in which the Eye and its appendages are situated The ear canal ( external auditory meatus, external acoustic meatus) is a tube running from the Outer ear to the Middle ear. This is the position where the subject is standing and looking directly forward. For comparison, the skulls of other species, notably primates and hominids, may sometimes be studied in the Frankfurt plane. A primate is a member of the biological order Primates ( Latin: "prime first rank" the group that contains Lemurs the Aye-aye A hominid is any member of the biological family Hominidae (the "great apes" including the extinct and extant Humans Chimpanzees However, this does not always equate to a natural posture in life.

Possible types of skull fractures

Main articles: Skull fracture, tripod fracture, and LeFort fracture

Other skulls

Temporal Fenestra

This Massospondylus skull shows the two temporal fenestrae typical of diapsids. A skull fracture is a break in one or more of the bones in the Skull caused by a Head injury. The tripod fracture, also called the zygomaticomaxillary complex or malar fracture, is composed of a set of fractures including the lateral orbital wall inferior LeFort fractures (also spelled as Le Fort fractures) are types of facial fractures that are classic in trauma Massospondylus (ˌmæsoʊˈspɒndɨləs from Greek, (massōn "longer" and (spondylos "vertebra" is a Genus of prosauropod Diapsids ("two arches" are a group of Reptiles that developed two holes ( Temporal fenestra) in each side of their Skulls about 300 Million

The temporal fenestra are anatomical features of the amniote skull, characterised by bilaterally symmetrical holes (fenestrae) in the temporal bone. The amniotes are a group of Tetrapod Vertebrates that include the Synapsida ( Mammals and Mammal-like reptiles and Sauropsida 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 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 The squamosal is a bone of the head of higher Vertebrates It is the principal component of the cheek region in the skull lying below the temporal series and 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 is 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 the more advanced sauropsids and synapsids did. As time progressed, sauropsids' and synapsids' temporal fenestrae became more modified and larger to make stronger bites and more jaw muscles. Dinosaurs, which are sauropsids, have large advanced openings and their descendants, the birds, have temporal fenestrae which have been modified. Mammals, which are synapsids, possess no fenestral openings in the skull, as the trait has been modified. They do, though, still have the temporal orbit (which resembles an opening) and the temporal muscles. It is a hole in the head and is situated to the rear of the orbit behind the eye.

Classification

Humans, despite having lost their fenestræ, are synapsids

There are four types of amniote skull, classified by the number and location of their fenestra. Synapsids ('fused arch' also known as theropsids ('beast face' are a class of Animals that includes Mammals and everything closer to mammals than 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. An anapsid is an Amniote whose skull does not have openings near the temples While "anapsid reptiles" or "anapsida" are traditionally Synapsids ('fused arch' also known as theropsids ('beast face' are a class of Animals that includes Mammals and everything closer to mammals than Euryapsida is a Polyphyletic (unnatural as the various members are not closely related group of Reptiles that are distinguished by a single temporal fenestra
Diapsida - two openings

Evolutionary, they are related as follows:

Amniota
- Class Synapsida
  - Order Therapsida
    - Class Mammalia - mammals
- Class Sauropsida - reptiles
  - Subclass Anapsida
  - (unranked) Eureptilia
    - Subclass Diapsida
      - (unranked) Euryapsida
      - Class Aves - birds