In human anatomy, theneurocranium, also known as thebraincase,brainpan,brain-pan,[1][2] orbrainbox, is the upper and back part of theskull, which forms a protective case around thebrain.[3] In the human skull, the neurocranium includes thecalvaria or skullcap. The remainder of the skull is thefacial skeleton.
Theossicles (three on each side) are usually not included as bones of the neurocranium.[6] There may variably also be extrasutural bones present.
Below the neurocranium is a complex of openings (foramina) and bones, including theforamen magnum which houses the neural spine. Theauditory bullae, located in the same region, aid in hearing.[7]
The size of the neurocranium is variable among mammals. The roof may contain ridges such as thetemporal crests.
The neurocranium arises fromparaxial mesoderm. There is also some contribution ofectomesenchyme. In Chondrichthyes and other cartilaginous vertebrates this portion of the cranium does not ossify; it is not replaced viaendochondral ossification.
The neurocranium is formed by the combination of theendocranium, the lower portions of thecranial vault, and theskull roof. Through the course ofevolution, the human neurocranium has expanded from comprising the back part of the mammalian skull to being also the upper part: during the evolutionary expansion of the brain, the neurocranium has overgrown thesplanchnocranium. The upper-frontmost part of the cranium also houses the evolutionarily newest part of the mammal brain, thefrontal lobes.
In other vertebrates, the foramen magnum is oriented towards the back, rather than downwards. The braincase contains a greater number of bones, most of which are endochondral rather than dermal:[8]
The singularbasioccipital is the rear lower part of the braincase, below the foramen magnum. It is homologous to thebasilar part of the occipital bone. In the ancestral tetrapod, the basioccipital makes up most of a large central knob-like surface, the occipital condyle, which articulates with the vertebrae as aball-and-socket joint. This plesiomorphic ("primitive") state is retained by modern reptiles and birds. The underside of the basioccipital may have a pair of large projections which act as neck muscle attachments: thebasitubera (also known as basioccipital tubera or basal tubera)
The paired exoccipitals (singular:exoccipital) are visible at the rear of the braincase, adjacent to the foramen magnum and above the basioccipital. They are homologous to thelateral parts of the occipital bone. Modern amphibians and mammals have independently acquired inflated exoccipitals, acting as pairedoccipital condyles while the basioccipital is reduced and loses its connection to the vertebrae.
The singularsupraoccipital is the rear upper part of the braincase, above the foramen magnum and below or behind the parietals orpostparietals. It is homologous to thesquamous part of the occipital bone, which is greatly enlarged in humans.
The paired opisthotics (singular:opisthotic) form most of the rear lateral part of the braincase, in front of the exoccipitals and above theforamen ovale. They also contribute to theparoccipital process, a lateral projection which acts as a buttress between the braincase and the outer skull bones. In many tetrapods, the opisthotic is fused to its corresponding exoccipital. Thejugular foramen is usually found near the point of fusion.
The paired prootics (singular:prootic) form the lateral part of the braincase, in front of the opisthotics. The front edge of the prootic is typically deeply notched by the exit hole for thetrigeminal nerve (V). Many other nerve exits are scattered among the prootic, opisthotic, and exoccipital. The prootic is homologous to thepetrous part of the temporal bone (in humans) or the petrosal bone (in other mammals).
The singularbasisphenoid forms the front lower part of the braincase, in front of the basioccipital and below the prootics. Each side of the basisphenoid hosts abasipterygoid process, a lateral rod which bends down and out to link to thepterygoid bones of the bony palate. The basisphenoid may also act as a component of the basitubera.
The singularparasphenoid is one of the few dermal components of the braincase, a flat plate below the basisphenoid. The parasphenoid acts as a component of the bony palate, wedging between the pterygoid bones and often ornamented with small tooth-like denticles. In many vertebrates the parasphenoid and basisphenoid are fused into a single bone, theparabasisphenoid. The front part of the parabasisphenoid is a blade-like structure, thecultriform process, which extends much further forward than the rest of the braincase.
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