# Endocranium

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{{Short description|Lower and inner parts of the skull}}
{{For|the internal cast of the cranium|Endocast}}
{{Infobox bone
| Name        = Endocranium
| Latin       = endocranium
| Image       = Endocranium.jpg
| Caption     = Human endocranium (pink fields), inner surface.
}}

The '''endocranium''' in [comparative anatomy](/source/comparative_anatomy) is a part of the [skull base](/source/Base_of_skull) in [vertebrates](/source/vertebrates) and it represents the basal, inner part of the [cranium](/source/cranium). The term is also applied to the outer layer of the [dura mater](/source/dura_mater) in [human anatomy](/source/human_anatomy).<ref>The American Heritage Medical Dictionary, 2004. Houghton Mifflin Company, USA</ref>

==Structure==
Structurally, the endocranium consists of a boxlike shape, open at the top. The posterior margin exhibits the ''[foramen magnum](/source/foramen_magnum)'', an opening for the [spinal cord](/source/spinal_cord). The floor of the endocranium has several paired openings for the [cranial nerves](/source/cranial_nerves), and the anterior margin holds a spongy construction, allowing for the [external nasal nerve](/source/external_nasal_nerve)s to pass through.<ref name="Romer, A 1977">[Romer, A.S](/source/Alfred_Romer). & T.S. Parsons. 1977. ''The Vertebrate Body.'' 5th ed. Saunders, Philadelphia. (6th ed. 1985)</ref> All bones of the structure derive from the [cranial neural crest](/source/cranial_neural_crest) during [fetal development](/source/fetal_development).

===Endocranial elements in humans===
In humans and other [mammal](/source/mammal)s, the endocranium forms during [fetal development](/source/fetal_development) as a cartilaginous [neurocranium](/source/neurocranium), that ossifies from  several centers.<ref>Kent, G.C & Miller, L. (1997): Comparative Anatomy of the Vertebrates. Wm. C. Brown Publishers. {{ISBN|0-697-24378-8}}.</ref> Several of these bones merge, and in the adult [primate](/source/primate)s (including humans), the endocranium is composed of only five bony elements (from front to back):<ref>''[Colbert, E.H.](/source/Edwin_Harris_Colbert) & Morales, M. (2001): [Colbert's Evolution of the Vertebrates: A History of the Backboned Animals Through Time](/source/Evolution_of_the_Vertebrates)''. 4th edition. John Wiley & Sons, Inc, New York - {{ISBN|978-0-471-38461-8}}.</ref>
* The [ethmoid](/source/ethmoid) bone, lying behind the nose.
* The [sphenoid bone](/source/sphenoid_bone), underlying the forward portion of the brain
* Paired [petrous part of the temporal bone](/source/petrous_part_of_the_temporal_bone)s, containing the [inner ear](/source/inner_ear) structures
* Most of the [occipital bone](/source/occipital_bone), surrounding the ''foramen magnum''
[Sexual dimorphism](/source/Sexual_dimorphism) in the prenatal period is observed, for example in the area of the [anterior cranial fossa](/source/anterior_cranial_fossa): the angle of the anterior fossa in male fetuses is greater than in female fetuses.<ref>{{Cite book |last=Kedzia |first=Alicja |title=Computer-aided scientific research. =: Komputerowe wspomaganie badań naukowych |last2=Derkowski |first2=Wojciech |last3=Glonek |first3=Michal |date=2007 |publisher=Wrocław Scientific Society |isbn=978-83-7374-050-1 |location=Wrocław |pages=247-252 |language=pl, en |chapter=Studies of sexual dimorphism and geometry of human skull and brain development during the fetal period using computer image analysis. = Badania dymorfizmu płciowego i geometrii rozwoju czaszki i mózgu człowieka w okresie płodowym z wykorzystaniem komputerowej analizy obrazu.}}</ref>

==Other animals==

===Endocranial components in other tetrapods===
The endocranium in [mammal](/source/mammal)s is much reduced in relative size and number of bones compared to the condition in the ancestral [land vertebrates](/source/tetrapod), though the [occipital bone](/source/occipital_bone) occur as one or more stout bony elements in several mammal groups. The occipital bone is also found as several bony elements in [birds](/source/birds) and [reptiles](/source/reptiles), while the skull of modern [amphibian](/source/amphibian)s is generally reduced with a simplified endocranium. The skull of early [labyrinthodonts](/source/Labyrinthodontia) were rather complex, and contained in addition to the bones mentioned above several small cartilaginous components that are fused to temporal and occipital bones in mammals:<ref name="Romer, A 1977"/>
* Paired [prootic](/source/prootic_bone) and [opisthotic](/source/opisthotic) bones above each ''[fenestra ovalis](/source/fenestra_ovalis)'', fused to the petrous part of the temporal bones in mammals.
* Paired [exoccipital bone](/source/exoccipital_bone)s medially and a single [basioccipital bone](/source/basioccipital_bone) below the ''foramen magnum'', part of the occipital bone in mammals.

===The endocranium in fish===
[[File:FishKeyDay.jpg|thumb|right|200 px|The loosely connected skull of a [perch](/source/perch).]]
While the endocranium is an integral part of the skull in mammals, [birds](/source/birds) and [reptiles](/source/reptiles), its connection to the [roofing parts](/source/skull_roof) of the skull is more loose in the [lower vertebrates](/source/anamniotes). In [Agnathans](/source/Agnathans) and [Chondrichthyes](/source/Chondrichthyes), the skull lacks the [skull roof](/source/skull_roof) dermal elements, their whole cranium being composed of the endocranium, properly called a [chondrocranium](/source/chondrocranium). In most [Osteichthyes](/source/Osteichthyes), the skull is only loosely joined, and the endocranial elements do not form a unit with the skull roof.

===Fossilization===
{{Main|Endocast}}

An endocast or endocranial cast is a cast made of the mold formed by the impression the [brain](/source/brain) makes on the inside of the [neurocranium](/source/neurocranium) (braincase), providing a replica of the brain with most of the details of its outer surface. Endocasts can also form naturally, when sediments fill the empty [skull](/source/skull), after which the skull is destroyed and the cast [fossil](/source/fossil)ized. Scientists are increasingly utilizing [computerized tomography](/source/computerized_tomography) scanning technology to create digital endocasts without damaging valuable specimens.  This gives a 3D representation of the brain.  Brain size and complexity can then be determined.

Endocasts were used for looking at the brains of ''Homo sapiens'' to find hemispheric specialization.

==See also==
*[Dermatocranium](/source/Dermatocranium)
*[Splanchnocranium](/source/Splanchnocranium)

==References==
{{Reflist}}

Category:Human anatomy
Category:Vertebrate anatomy

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Adapted from the Wikipedia article [Endocranium](https://en.wikipedia.org/wiki/Endocranium) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Endocranium?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.