# Sphenoid bone

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{{Short description|Bone of the neurocranium}}
{{Anatomy-terms}}
{{Infobox bone 
| Name = Sphenoid bone 
| Latin = os sphenoidale 
| Image = File:Sphenoid bone - lateral view.png
| Caption = Position of the sphenoid bone
| Image2 = File:Sphenoid bone - animation 02.gif
| Caption2 = Animation of the sphenoid bone
| Width = 300 
| Articulations =
}}

The '''sphenoid bone'''{{refn|name=note|group=note|According to most dictionaries, the word ''sphenoid'' ({{IPAc-en|ˈ|s|f|iː|n|ɔɪ|d}}<ref>''[OED](/source/OED)'' 2nd edition, 1989.</ref><ref>[http://www.merriam-webster.com/dictionary/sphenoid Entry "sphenoid"] in ''[http://www.merriam-webster.com/ Merriam-Webster Online Dictionary]''.</ref>) derives from Greek ''sphenoeides'', "wedgelike". Thieme Atlas of Anatomy<ref>Thieme Atlas of Anatomy, Head and Neuroanatomy 2011</ref> disagrees and says that the sphenoid bone was originally called ''os sphecoidale'', meaning "bone resembling a wasp", and that the word was later written 'sphenoidale' by a transcription error. As an anterior view of the bone resembles more the body of a wasp or a bat<ref name="Human Anatomy Volume Three">{{cite book|last1=Chaurasia|title=Human Anatomy Volume Three|date=31 January 2013|publisher=CBS Publishers & Distributors|isbn=978-81-239-2332-1|pages=43–45}}</ref> with wings than a wedge.}} is an unpaired [bone](/source/bone) of the [neurocranium](/source/neurocranium). It is situated in the middle of the [skull](/source/skull) towards the front, in front of the [basilar part of the occipital bone](/source/basilar_part_of_occipital_bone). The sphenoid bone is one of the seven bones that articulate to form the [orbit](/source/orbit_(anatomy)). Its shape somewhat resembles that of a [butterfly](/source/butterfly), [bat](/source/bat) or [wasp](/source/wasp) with its wings extended. The name presumably originates from this shape, since {{Lang|grc-latn|sphekodes}} ({{Lang|grc|σφηκώδης}}) means {{Gloss|wasp-like}} in [Ancient Greek](/source/Ancient_Greek).

==Structure==
[[File:Orbital bones.png|thumb|left|200px|Seven bones articulate to form the [orbit](/source/orbit_(anatomy)). The sphenoid bone is in red (directly in the middle of the [orbital cavity](/source/orbital_cavity))]]
thumb|right|200px|Wedge-shaped sphenoid bone seen laterally
It is divided into the following parts:
* a median portion, known as the [body of sphenoid bone](/source/body_of_sphenoid_bone), containing the [sella turcica](/source/sella_turcica), which houses the [pituitary gland](/source/pituitary_gland) as well as the paired paranasal sinuses, the [sphenoidal sinuses](/source/sphenoidal_sinuses)<ref>{{cite book |title=Human Anatomy |last=Jacob |publisher=Elsevier |year=2008 |page=211 |isbn=978-0-443-10373-5 }}</ref>
* two [greater wings](/source/Greater_wing_of_sphenoid_bone) on the lateral side of the body and two [lesser wings](/source/Lesser_wing_of_sphenoid_bone) from the anterior side.
* [Pterygoid processes of the](/source/Pterygoid_processes_of_the_sphenoid) sphenoid, directed downwards from the junction of the body and the greater wings. <ref name="Human Anatomy Volume Three">{{cite book|last1=Chaurasia|title=Human Anatomy Volume Three|date=31 January 2013|publisher=CBS Publishers & Distributors|isbn=978-81-239-2332-1|pages=43–45}}</ref>

Two [sphenoidal conchae](/source/sphenoidal_conchae) are situated at the anterior and inferior part of the body.

=== Intrinsic ligaments of the sphenoid ===
The more important of these are: 
* the [pterygospinous](/source/Pterygospinous_ligament), which stretches between the [spina angularis](/source/spina_angularis) and the [lateral pterygoid plate](/source/lateral_pterygoid_plate), superiorly attached to the root of the lateral pterygoid plate anteriorly; 
* the interclinoid ligament, a band of [dura mater](/source/dura_mater) that connects the [anterior clinoid process](/source/anterior_clinoid_process) and [posterior clinoid process](/source/posterior_clinoid_process) of the sphenoid bone;
* the caroticoclinoid, connecting the anterior to the [middle clinoid process](/source/middle_clinoid_process).

These ligaments occasionally [ossify](/source/Ossification), though the incidence of ligamentous ossification (both partial and complete) varies according to the ligament type, with the interclinoid ligament being most commonly identified as having ossified and the [pterygoalar ligament](/source/pterygoalar_ligament) least commonly identified. <ref>Touska, P., Hasso, S., Oztek, A. et al. Skull base ligamentous mineralisation: evaluation using computed tomography and a review of the clinical relevance. Insights Imaging 10, 55 (2019). https://doi.org/10.1186/s13244-019-0740-8</ref>

===Features===
* [pterygoid notch](/source/pterygoid_notch)
* [pterygoid fossa](/source/pterygoid_fossa)
* [scaphoid fossa](/source/scaphoid_fossa)
* [pterygoid hamulus](/source/pterygoid_hamulus)
* [pterygoid canal](/source/pterygoid_canal)
* [pterygospinous process](/source/pterygospinous_process)
* [sella turcica](/source/sella_turcica)

===Articulations===
The sphenoid articulates with the [frontal](/source/Frontal_bone), [parietal](/source/Parietal_bone), [ethmoid](/source/Ethmoid_bone), [temporal](/source/Temporal_bone), [zygomatic](/source/Zygomatic_bone), [palatine](/source/Palatine_bone), [vomer](/source/vomer_bone), and [occipital](/source/Occipital_bone) bones and helps to connect the [neurocranium](/source/neurocranium) to the [facial skeleton](/source/facial_skeleton).

==Body of sphenoid==

===Superior or cerebral surface===

Articulates with [ethmoid bone](/source/ethmoid_bone) anteriorly and basilar part of [occipital bone](/source/occipital_bone) posteriorly.
It shows:
# [Jugum sphenoidale](/source/Os_sphenoidale)
# [Sulcus chiasmaticus](/source/Sulcus_chiasmaticus)
# [Tuberculum sellae](/source/Tuberculum_sellae)
# [Sella turcica](/source/Sella_turcica)
# [Dorsum sellae](/source/Dorsum_sellae)
# [Clivus](/source/Clivus_(anatomy))<ref name="Human Anatomy Volume Three">{{cite book|last1=Chaurasia|title=Human Anatomy Volume Three|date=31 January 2013|publisher=CBS Publishers & Distributors|isbn=978-81-239-2332-1|pages=43–45}}</ref>

===Inferior surface===

# [Rostrum](/source/Rostrum_(anatomy)) of sphenoid
# [Sphenoidal conchae](/source/Sphenoidal_conchae)
# Vaginal processes of [medial pterygoid plate](/source/medial_pterygoid_plate)

===Anterior surface===

Sphenoidal crest articulates with the perpendicular plate of [the ethmoid,](/source/ethmoid) leading to the formation of a part of the septum of nose.

===Posterior surface===

[Basilar part of occipital bone](/source/Basilar_part_of_occipital_bone)

===Lateral surface===

[Carotid sulcus](/source/Carotid_sulcus) lodging [cavernous sinus](/source/cavernous_sinus) and [internal carotid artery](/source/internal_carotid_artery)

==Sphenoidal sinuses==
Sphenoidal or [sphenoid sinus](/source/sphenoid_sinus)es are asymmetrical air sinuses in the body of the sphenoid, closed by [sphenoidal conchae](/source/sphenoidal_conchae).

==Greater wings==
{{See also|Greater wing of the sphenoid bone}}

===Superior or cerebral surface===

This forms the floor of the [middle cranial](/source/middle_cranial_fossa) fossa. It presents (starting from the front):
* [foramen rotundum](/source/foramen_rotundum)
* [foramen ovale](/source/Foramen_ovale_(skull))
*[Sphenoidal emissary foramen](/source/Sphenoidal_emissary_foramen)
* [foramen spinosum](/source/foramen_spinosum)<ref name="Human Anatomy Volume Three">{{cite book|last1=Chaurasia|title=Human Anatomy Volume Three|date=31 January 2013|publisher=CBS Publishers & Distributors|isbn=978-81-239-2332-1|pages=43–45}}</ref>

===Lateral surface===

This is divided into (by [infratemporal crest](/source/infratemporal_crest)):
* Upper or [temporal surface](/source/temporal_surface)
* Lower or [infratemporal surface](/source/infratemporal_surface)<ref name="Human Anatomy Volume Three">{{cite book|last1=Chaurasia|title=Human Anatomy Volume Three|date=31 January 2013|publisher=CBS Publishers & Distributors|isbn=978-81-239-2332-1|pages=43–45}}</ref>

[Foramen](/source/Foramen) pierce it:
* [Foramen ovale](/source/Foramen_ovale_(skull))
* [Foramen spinosum](/source/Foramen_spinosum)<ref name="Human Anatomy Volume Three"></ref>

===Orbital surface===
This forms the posterior wall of the [orbit](/source/Orbit_(anatomy))<ref name="Human Anatomy Volume Three">{{cite book|last1=Chaurasia|title=Human Anatomy Volume Three|date=31 January 2013|publisher=CBS Publishers & Distributors|isbn=978-81-239-2332-1|pages=43–45}}</ref>

==Lesser wings==
These are two triangular wings projecting laterally from the anterosuperior part of the body.  Each consists of:
* A base forming medial end of the wing.
* Tip forming the lateral end of the wing.
* Superior surface forming the floor of [anterior cranial fossa](/source/anterior_cranial_fossa).
* Inferior surface forming upper boundary of [superior orbital fissure](/source/superior_orbital_fissure).
* Posterior surface projects into the [Sylvian point](/source/Sylvian_point).
* Medially, terminates in the anterior clinoid process. <ref name="Human Anatomy Volume Three">{{cite book|last1=Chaurasia|title=Human Anatomy Volume Three|date=31 January 2013|publisher=CBS Publishers & Distributors|isbn=978-81-239-2332-1|pages=43–45}}</ref>

===Development===
thumb|230px|'''Figure 4 :''' Sphenoid bone at birth, posterior aspect.
Until the seventh or eighth month of [fetal development](/source/prenatal_development), the body of the sphenoid consists of two parts: one in front of the [tuberculum sellae](/source/tuberculum_sellae), the presphenoid, with which the small wings are continuous; the other, consisting of the [sella turcica](/source/sella_turcica) and [dorsum sellae](/source/dorsum_sellae), the postsphenoid, with which are associated the great wings, and pterygoid processes.

The greater part of the bone is ossified in cartilage. There are fourteen centers in all, six for the presphenoid and eight for the postsphenoid.

==== Presphenoid ====
By about the ninth week of [fetal development](/source/prenatal_development) an ossific center appears for each of the [small wings](/source/Lesser_wing_of_sphenoid_bone) (orbito-sphenoids) just lateral to the [optic foramen](/source/optic_foramen); this is followed by the appearance of two nuclei in the [presphenoid](/source/presphenoid) part of the body.

The sphenoidal conchae are each developed from a center that makes its appearance about the fifth month; at birth they consist of small triangular laminae, and it is not until the third year that they become hollowed out and coneshaped; about the fourth year they fuse with the labyrinths of the [ethmoid bone](/source/ethmoid_bone), and between the ninth and twelfth years they unite with the sphenoid bone.

==== Postsphenoid ====
The first ossific nuclei are those for the great wings ([alisphenoid](/source/alisphenoid)s). One makes its appearance in each wing between the [foramen rotundum](/source/foramen_rotundum) and [foramen ovale](/source/Foramen_ovale_(skull)) about the eighth week. The orbital plate and that part of the sphenoid, which is found in the temporal fossa, as well as the lateral pterygoid plate, are ossified in membrane (Fawcett).

Soon after, the centers for the [postsphenoid part of the body](/source/basisphenoid) appear, one on either side of the sella turcica, and become blended together about the middle of fetal life.

Each [medial pterygoid plate](/source/pterygoid_bone) (except its hamulus) is ossified in membrane, and its center probably appears about the ninth or tenth week; the hamulus becomes chondrified during the third month, and almost at once ossifies (Fawcett).

The medial joins the lateral pterygoid plate about the sixth month.

About the fourth month, a center appears for each lingula and speedily joins the rest of the bone.

The [presphenoid](/source/presphenoid) is united to the postsphenoid about the eighth month, and at birth the sphenoid is in three pieces [Fig. 4]: a central one, consisting of the body and small wings, and two lateral, each comprising a great wing and pterygoid process.

In the first year after birth the great wings and body unite, and the small wings extend inward above the anterior part of the body and, meeting with each other in the middle line, form an elevated smooth surface, termed the jugum sphenoidale.

By the twenty-fifth year the sphenoid and occipital are completely fused.

Between the pre- and postsphenoid there are occasionally seen the remains of a canal, the canalis cranio-pharyngeus, through which, in early fetal life, the hypophyseal diverticulum of the buccal [ectoderm](/source/ectoderm) is transmitted.

The sphenoidal sinuses are present as minute cavities at the time of birth (Onodi), but do not attain their full size until after puberty.

==Function==
This bone assists with the formation of the base and the sides of the skull and the floors and walls of the orbits. It is the site of attachment for most of the muscles of [mastication](/source/mastication). Many foramina and fissures are located in the sphenoid that carry nerves and blood vessels of the head and neck, such as the [superior orbital fissure](/source/superior_orbital_fissure) (with [ophthalmic nerve](/source/ophthalmic_nerve)), [foramen rotundum](/source/foramen_rotundum) (with [maxillary nerve](/source/maxillary_nerve)) and [foramen ovale](/source/Foramen_ovale_(skull)) (with [mandibular nerve](/source/mandibular_nerve)).<ref>{{cite book |title=Illustrated Anatomy of the Head and Neck |last1=Fehrenbach |last2=Herring |publisher=Elsevier |year=2012 |page=52 |isbn=978-1-4377-2419-6 }}</ref>

==Other animals==

The sphenoid bone of humans is [homologous](/source/homology_(biology)) with a number of bones that are often separate in other animals, and have a somewhat complex arrangement.

In the early [lobe-finned fish](/source/lobe-finned_fish)es and [tetrapod](/source/tetrapod)s, the pterygoid bones were flat, ribbon-like bones forming the major part of the roof of the mouth. Above the pterygoids were the epipterygoid bones, which formed part of a flexible joint between the braincase and the palatal region, as well as extending a vertical bar of bone towards the roof of the skull. The basisphenoid bone formed part of the floor of the braincase. Above them, the orbitosphenoid forms the interorbital wall. <ref name=VB>{{cite book |author=Romer, Alfred Sherwood|author2=Parsons, Thomas S.|year=1977 |title=The Vertebrate Body |publisher=Holt-Saunders International |location= Philadelphia, PA|pages= 220–244|isbn= 0-03-910284-X}}</ref>

Aside from the loss of the flexible joint at the rear of the palate, this primitive pattern is broadly retained in [reptile](/source/reptile)s, albeit with some individual modifications. In [bird](/source/bird)s, the epipterygoids are absent. Living [amphibian](/source/amphibian)s have a relatively simplified skull in this region; a broad parasphenoid forms the floor of the braincase, the pterygoids are relatively small, and all other related bones except the sphenethmoid are absent. <ref name=VB/>

In [mammal](/source/mammal)s, these various bones are often (though not always) fused into a single structure, the sphenoid. The basisphenoid forms the posterior part of the base, while the pterygoid processes represent the pterygoid bones. The epipterygoids have extended into the wall of the cranium; they are referred to as [alisphenoid](/source/alisphenoid)s when separate in mammals and form the greater wings of the sphenoid when fused into a larger structure. The [orbitosphenoid](/source/orbitosphenoid)s bone forms the lesser wings and a new separate bone, the presphenoid, forms the anterior part of the base. <ref name=VB/>

In the [dog,](/source/dog) the sphenoid is represented by eight bones: basisphenoid, alisphenoids, presphenoid, orbitosphenoids, and pterygoids. These bones remain separate and are the:
*2 [Alisphenoid](/source/Alisphenoid)s: each greater wing
*2 [Orbitosphenoid](/source/Orbitosphenoid)s: each lesser wing
*[Basisphenoid](/source/Basisphenoid): back part of body
*[Presphenoid](/source/Presphenoid): front part of body
*2 [Pterygoids](/source/Pterygoid_processes_of_the_sphenoid): medial pterygoid plate

==Additional images==
<gallery>
File:Sphenoid bone - animation.gif|Position of sphenoid bone (shown in green). Animation.
File:Sphenoid bone - inferior view animation.gif|Seen from below ([mandible](/source/mandible) is removed)
File:Sphenoid bone - superior view animation2.gif|Seen from above ([parietal bones](/source/Parietal_bone) are removed)
File:Sphenoid bone - close-up - animation.gif|Shape of sphenoid bone.
File:Illu facial bones.jpg|Facial bones.
File:Gray153.png|Lateral wall of nasal cavity, showing ethmoid bone in position.
File:Gray187.png|Base of skull. Inferior surface.
File:Gray188.png|Lateral view of the skull.
File:Gray191.png|Horizontal section of nasal and orbital cavities.
File:Gray193.png|Floor of the skull.
File:Gray196.png|Roof, floor, and lateral wall of left nasal cavity.
File:Gray190.png|The skull from the front. The sphenoid is labeled with yellow to the left of the picture, both in the orbit and behind the zygomatic process
File:Cranium 4.jpg|Sphenoid bone
File:Sphenoid bone - superior view.jpg|Sphenoid bone superior view
File:Sphenoid and temporal bones.jpg|Sphenoid bone and temporal bones
</gallery>

==See also==
{{Commons category|Sphenoid bones}}
*[Sphenoidal sinus](/source/Sphenoidal_sinus)
*[Pterygospinal ligament](/source/Pterygospinal_ligament)
*[Basilar skull fracture](/source/Basilar_skull_fracture)

==Notes==
{{Reflist|group=note}}

==References==
{{Reflist}}

{{Gray's}}

==External links==
*{{SUNYAnatomyFigs|22|01|06}} - "Lateral view of skull."

{{Cranium}}
{{Orbital anatomy}}
{{Portal bar|Anatomy}}
{{Authority control}}

Category:Bones of the head and neck
Category:Otorhinolaryngology

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