imported>Skunkiix at 03:52, 29 March 2025

2025-03-29T03:52:55Z

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{{short description|The 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]] is a part of the [[Base of skull|skull base]] in [[vertebrates]] and it represents the basal, inner part of the [[cranium]]. The term is also applied to the outer layer of the [[dura mater]] in [[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]]'', an opening for the [[spinal cord]]. The floor of the endocranium has several paired openings for the [[cranial nerves]], and the anterior margin holds a spongy construction, allowing for the [[external nasal nerve]]s to pass through.<ref name="Romer, A 1977">[[Alfred Romer|Romer, A.S]]. & 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]] during [[fetal development]].

===Endocranial elements in humans===
In humans and other [[mammal]]s, the endocranium forms during [[fetal development]] as a cartilaginous [[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]]s (including humans), the endocranium is composed of only five bony elements (from front to back):<ref>''[[Edwin Harris Colbert|Colbert, E.H.]] & Morales, M. (2001): [[Evolution of the Vertebrates|Colbert's Evolution of the Vertebrates: A History of the Backboned Animals Through Time]]''. 4th edition. John Wiley & Sons, Inc, New York - {{ISBN|978-0-471-38461-8}}.</ref>
* The [[ethmoid]] bone, lying behind the nose.
* The [[sphenoid bone]], underlying the forward portion of the brain
* Paired [[petrous part of the temporal bone]]s, containing the [[inner ear]] structures
* Most of the [[occipital bone]], surrounding the ''foramen magnum''

==Other animals==

===Endocranial components in other tetrapods===
The endocranium in [[mammal]]s is much reduced in relative size and number of bones compared to the condition in the ancestral [[tetrapod|land vertebrates]], though the [[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]] and [[reptiles]], while the skull of modern [[amphibian]]s is generally reduced with a simplified endocranium. The skull of early [[Labyrinthodontia|labyrinthodonts]] 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 bone|prootic]] and [[opisthotic]] bones above each ''[[fenestra ovalis]]'', fused to the petrous part of the temporal bones in mammals.
* Paired [[exoccipital bone]]s medially and a single [[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]].]]
While the endocranium is an integral part of the skull in mammals, [[birds]] and [[reptiles]], its connection to the [[skull roof|roofing parts]] of the skull is more loose in the [[anamniotes|lower vertebrates]]. In [[Agnathans]] and [[Chondrichthyes]], the skull lacks the [[skull roof]] dermal elements, their whole cranium being composed of the endocranium, properly called a [[chondrocranium]]. In most [[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]] makes on the inside of the [[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]], after which the skull is destroyed and the cast [[fossil]]ized. Scientists are increasingly utilizing [[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]]
*[[Splanchnocranium]]

==References==
{{Reflist}}

[[Category:Human anatomy]]
[[Category:Vertebrate anatomy]]

Endocranium - Revision history

imported>Skunkiix at 03:52, 29 March 2025