The sphenoid bone is an unpaired
bone
A bone is a Stiffness, rigid Organ (biology), organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red blood cell, red and white blood cells, store minerals, provid ...
of the
neurocranium
In human anatomy, the neurocranium, also known as the braincase, brainpan, or brain-pan is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calvaria (skull), ...
. It is situated in the middle of the
skull
The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...
towards the front, in front of the
basilar part of the occipital bone. The sphenoid bone is one of the seven bones that articulate to form the
orbit
In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...
. Its shape somewhat resembles that of a
butterfly
Butterflies are insects in the macrolepidopteran clade Rhopalocera from the Order (biology), order Lepidoptera, which also includes moths. Adult butterflies have large, often brightly coloured wings, and conspicuous, fluttering flight. The ...
or
bat
Bats are mammals of the order Chiroptera.''cheir'', "hand" and πτερόν''pteron'', "wing". With their forelimbs adapted as wings, they are the only mammals capable of true and sustained flight. Bats are more agile in flight than most bi ...
with its wings extended.
Structure
![Orbital bones](https://upload.wikimedia.org/wikipedia/commons/8/8d/Orbital_bones.png)
It is divided into the following parts:
* a median portion, known as the
body of sphenoid bone
The body of the sphenoid bone, more or less cubical in shape, is hollowed out in its interior to form two large cavities, the sphenoidal sinuses, which are separated from each other by a septum.
Superior surface
The superior surface of the body ...
, containing the
sella turcica
The sella turcica (Latin for 'Turkish saddle') is a saddle-shaped depression in the body of the sphenoid bone of the human skull and of the skulls of other hominids including chimpanzees, gorillas and orangutans. It serves as a cephalometric la ...
, which houses the
pituitary gland
In vertebrate anatomy, the pituitary gland, or hypophysis, is an endocrine gland, about the size of a chickpea and weighing, on average, in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain. The ...
as well as the paired paranasal sinuses, the
sphenoidal sinuses
The sphenoid sinus is a paired paranasal sinus occurring within the within the body of the sphenoid bone. It represents one pair of the four paired paranasal sinuses.Illustrated Anatomy of the Head and Neck, Fehrenbach and Herring, Elsevier, 2012, ...
* two
greater wings on the lateral side of the body and two
lesser wings from the anterior side.
*
Pterygoid processes of the sphenoid
The pterygoid processes of the sphenoid (from Greek ''pteryx'', ''pterygos'', "wing"), one on either side, descend perpendicularly from the regions where the body and the greater wings of the sphenoid bone unite.
Each process consists of a medi ...
es, directed downwards from the junction of the body and the greater wings.
Two
sphenoidal conchae
The sphenoidal conchae (sphenoidal turbinated processes) are two thin, curved plates, situated at the anterior and lower part of the body of the sphenoid. An aperture of variable size exists in the anterior wall of each, and through this the sphen ...
are situated at the anterior and inferior part of the body.
Intrinsic ligaments of the sphenoid
The more important of these are:
* the pterygospinous, stretching between the
spina angularis
The sphenoidal spine (Latin: "''spina angularis''") is a downwardly directed process at the apex of the great wings of the sphenoid bone that serves as the origin of the sphenomandibular ligament.
Additional images
File:Spine of sphenoid bone. ...
and the
lateral pterygoid plate
The pterygoid processes of the sphenoid (from Greek ''pteryx'', ''pterygos'', "wing"), one on either side, descend perpendicularly from the regions where the body and the greater wings of the sphenoid bone unite.
Each process consists of a medi ...
(see
cervical fascia
The cervical fascia is fascia found in the region of the neck.
It usually refers to the deep cervical fascia. However, there is also a superficial cervical fascia Superficial cervical fascia is a thin layer of subcutaneous connective tissue that ...
);
* the interclinoid, a fibrous process joining the
anterior
Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
to the
posterior clinoid process
In the sphenoid bone, the anterior boundary of the sella turcica is completed by two small eminences, one on either side, called the anterior clinoid processes, while the posterior boundary is formed by a square-shaped plate of bone, the dorsum sel ...
;
* and the caroticoclinoid, connecting the anterior to the
middle clinoid process
The anterior boundary of the sella turcica is completed by two small eminences, one on either side, called the middle clinoid processes. It is found lateral to the sella turcica.
Etymology
Clinoid likely comes from the Greek root ''klinein'' or ...
.
These ligaments occasionally ossify.
Features
*
pterygoid notch
Pterygoid notch (incisura pterygoidea) is a notch on the inferior portion of the pterygoid processes
The pterygoid processes of the sphenoid (from Greek ''pteryx'', ''pterygos'', "wing"), one on either side, descend perpendicularly from the re ...
*
pterygoid fossa
The pterygoid fossa is an anatomical term for the fossa formed by the divergence of the lateral pterygoid plate and the medial pterygoid plate of the sphenoid bone.
Structure
The lateral and medial pterygoid plates (of the pterygoid process of ...
*
scaphoid fossa
In the pterygoid processes of the sphenoid, above the pterygoid fossa is a small, oval, shallow depression, the scaphoid fossa, which gives origin to the Tensor veli palatini
The tensor veli palatini muscle (tensor palati or tensor muscle of the ...
*
pterygoid hamulus
The pterygoid hamulus is a hook-like process at the lower extremity of the medial pterygoid plate of the sphenoid bone of the skull. It is the superior origin of the pterygomandibular raphe, and the levator veli palatini muscle.
Structure
The p ...
*
pterygoid canal
The pterygoid canal (also vidian canal) is a passage in the sphenoid bone of the skull leading from just anterior to the foramen lacerum in the middle cranial fossa to the pterygopalatine fossa.
Structure
The pterygoid canal runs through the medi ...
*
pterygospinous process
Pterygospinous process, also known as the Civinini process or processus pterygospinosus, is a sharp spine on the posterior edge of the lateral pterygoid plate
The pterygoid processes of the sphenoid (from Greek ''pteryx'', ''pterygos'', "wing"), ...
*
sella turcica
The sella turcica (Latin for 'Turkish saddle') is a saddle-shaped depression in the body of the sphenoid bone of the human skull and of the skulls of other hominids including chimpanzees, gorillas and orangutans. It serves as a cephalometric la ...
Articulations
The sphenoid articulates with the
frontal
Front may refer to:
Arts, entertainment, and media Films
* ''The Front'' (1943 film), a 1943 Soviet drama film
* ''The Front'', 1976 film
Music
* The Front (band), an American rock band signed to Columbia Records and active in the 1980s and e ...
,
parietal,
ethmoid
The ethmoid bone (; from grc, ἡθμός, hēthmós, sieve) is an unpaired bone in the skull that separates the nasal cavity from the brain. It is located at the roof of the nose, between the two orbits. The cubical bone is lightweight due to a ...
,
temporal,
zygomatic,
palatine
A palatine or palatinus (in Latin; plural ''palatini''; cf. derivative spellings below) is a high-level official attached to imperial or royal courts in Europe since Roman times. ,
vomer
The vomer (; lat, vomer, lit=ploughshare) is one of the unpaired facial bones of the skull. It is located in the midsagittal line, and articulates with the sphenoid, the ethmoid, the left and right palatine bones, and the left and right maxill ...
, and
occipital
The occipital bone () is a cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone overlies the occipital lobes of the cereb ...
bones and helps to connect the
neurocranium
In human anatomy, the neurocranium, also known as the braincase, brainpan, or brain-pan is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calvaria (skull), ...
to the
facial skeleton
The facial skeleton comprises the ''facial bones'' that may attach to build a portion of the skull. The remainder of the skull is the braincase.
In human anatomy and development, the facial skeleton is sometimes called the ''membranous viscerocr ...
.
Body of sphenoid
Superior or cerebral surface
Articulates with
ethmoid bone
The ethmoid bone (; from grc, ἡθμός, hēthmós, sieve) is an unpaired bone in the skull that separates the nasal cavity from the brain. It is located at the roof of the nose, between the two orbits. The cubical bone is lightweight due to a ...
anteriorly and basilar part of
occipital bone
The occipital bone () is a neurocranium, cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone overlies the occipital lobe ...
posteriorly.
It shows:
#
Jugum sphenoidale
#
Sulcus chiasmaticus
#
Tuberculum sellae
The tuberculum sellae (or the tubercle of the sella turcica) is a part of the sphenoid bone
The sphenoid bone is an unpaired bone of the neurocranium. It is situated in the middle of the skull towards the front, in front of the basilar part of ...
#
Sella turcica
The sella turcica (Latin for 'Turkish saddle') is a saddle-shaped depression in the body of the sphenoid bone of the human skull and of the skulls of other hominids including chimpanzees, gorillas and orangutans. It serves as a cephalometric la ...
#
Dorsum sellae
The dorsum sellae is part of the sphenoid bone in the skull. Together with the basilar part of the occipital bone it forms the clivus.
In the sphenoid bone, the anterior boundary of the sella turcica is completed by two small eminences, one on e ...
#
Clivus
Inferior surface
#
Rostrum
Rostrum may refer to:
* Any kind of a platform for a speaker:
**dais
**pulpit
* Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects
* Rostrum (ship), a form of bow on naval ships
* Ros ...
of sphenoid
#
Sphenoidal conchae
The sphenoidal conchae (sphenoidal turbinated processes) are two thin, curved plates, situated at the anterior and lower part of the body of the sphenoid. An aperture of variable size exists in the anterior wall of each, and through this the sphen ...
# Vaginal processes of
medial pterygoid plate
The pterygoid processes of the sphenoid (from Greek ''pteryx'', ''pterygos'', "wing"), one on either side, descend perpendicularly from the regions where the body and the greater wings of the sphenoid bone unite.
Each process consists of a me ...
Anterior surface
Sphenoidal crest articulates with the perpendicular plate of
ethmoid
The ethmoid bone (; from grc, ἡθμός, hēthmós, sieve) is an unpaired bone in the skull that separates the nasal cavity from the brain. It is located at the roof of the nose, between the two orbits. The cubical bone is lightweight due to a ...
leading to formation of a part of the septum of nose.
Posterior surface
Basilar part of occipital bone
The basilar part of the occipital bone (also basioccipital) extends forward and upward from the foramen magnum, and presents in front an area more or less quadrilateral in outline.
In the young skull this area is rough and uneven, and is joined ...
Lateral surface
Carotid sulcus
The carotid groove is an anatomical groove in the sphenoid bone located above the attachment of each great wing of the sphenoid bone. The groove is curved like the italic letter f, and lodges the internal carotid artery and the cavernous sinus
Th ...
lodging
cavernous sinus
The cavernous sinus within the human head is one of the dural venous sinuses creating a cavity called the lateral sellar compartment bordered by the temporal bone of the skull and the sphenoid bone, lateral to the sella turcica.
Structure
The cave ...
and
internal carotid artery
The internal carotid artery (Latin: arteria carotis interna) is an artery in the neck which supplies the anterior circulation of the brain. In human anatomy, the internal and external carotids arise from the common carotid arteries, where these b ...
Sphenoidal sinuses
Sphenoidal sinus
The sphenoid sinus is a paired paranasal sinus occurring within the within the body of the sphenoid bone. It represents one pair of the four paired paranasal sinuses.Illustrated Anatomy of the Head and Neck, Fehrenbach and Herring, Elsevier, 2012, ...
es are asymmetrical air sinuses in the body of the sphenoid, closed by
sphenoidal conchae
The sphenoidal conchae (sphenoidal turbinated processes) are two thin, curved plates, situated at the anterior and lower part of the body of the sphenoid. An aperture of variable size exists in the anterior wall of each, and through this the sphen ...
.
Greater wings
Superior or cerebral surface
This forms the floor of the
middle cranial fossa
The middle cranial fossa, deeper than the anterior cranial fossa, is narrow medially and widens laterally to the sides of the skull. It is separated from the posterior fossa by the clivus and the petrous crest.
It is bounded in front by the pos ...
. It presents (starting from the front):
*
foramen rotundum
The foramen rotundum is a circular hole in the sphenoid bone of the skull. It connects the middle cranial fossa and the pterygopalatine fossa. It allows for the passage of the maxillary nerve (V2), a branch of the trigeminal nerve.
Structure
T ...
*
foramen ovale
*
Sphenoidal emissary foramen
In the base of the skull, in the great wings of the sphenoid bone, medial to the foramen ovale, a small aperture, the sphenoidal emissary foramen, may occasionally be seen (it is often absent) opposite the root of the pterygoid process. When prese ...
*
foramen spinosum
The foramen spinosum is a hole located in the greater wing of the sphenoid. It is located posterolateral to the foramen ovale and anterior to the sphenoidal spine. It allows the passage of the middle meningeal artery, middle meningeal vein and ...
Lateral surface
This is divided into (by
infratemporal crest
The lateral surface of the greater wing of the sphenoid is convex, and divided by a transverse ridge, the infratemporal crest, into two portions.
The superior or temporal portion, convex from above downward, concave from before backward, forms a ...
):
* Upper or
temporal surface
In the human skull, the zygomatic bone (from grc, ζῠγόν, zugón, yoke), also called cheekbone or malar bone, is a paired irregular bone which articulates with the maxilla, the temporal bone, the sphenoid bone and the frontal bone. It is s ...
* Lower or
infratemporal surface
pierce it:
*
Foramen ovale
*
Foramen spinosum
The foramen spinosum is a hole located in the greater wing of the sphenoid. It is located posterolateral to the foramen ovale and anterior to the sphenoidal spine. It allows the passage of the middle meningeal artery, middle meningeal vein and ...
Orbital surface
This forms the posterior wall of the
orbit
In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...
Lesser wings
These are two triangular wings projecting laterally from 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 floor of
anterior cranial fossa
The anterior cranial fossa is a depression in the floor of the cranial base which houses the projecting frontal lobes of the brain. It is formed by the orbital part of frontal bone, orbital plates of the Frontal bone, frontal, the cribriform plate ...
.
* Inferior surface forming upper boundary of
superior orbital fissure
The superior orbital fissure is a foramen or cleft of the skull between the lesser and greater wings of the sphenoid bone. It gives passage to multiple structures, including the oculomotor nerve, trochlear nerve, ophthalmic nerve, abducens ner ...
.
* Posterior surface projects into the
Sylvian point
The Sylvian point is the point on the human skull nearest the Sylvian fissure and is located about 30 millimeters behind the zygomatic process of frontal bone. It is the name given to the stem of the lateral sulcus of the brain. It is named after ...
.
* Medially, terminates in the anterior clinoid process.
Development
![Gray148](https://upload.wikimedia.org/wikipedia/commons/d/d3/Gray148.png)
Until the seventh or eighth month of
fetal development
Prenatal development () includes the development of the embryo and of the fetus during a viviparous animal's gestation. Prenatal development starts with fertilization, in the germinal stage of embryonic development, and continues in fetal devel ...
, the body of the sphenoid consists of two parts: one in front of the
tuberculum sellæ, the presphenoid, with which the small wings are continuous; the other, consisting of the
sella turcica
The sella turcica (Latin for 'Turkish saddle') is a saddle-shaped depression in the body of the sphenoid bone of the human skull and of the skulls of other hominids including chimpanzees, gorillas and orangutans. It serves as a cephalometric la ...
and
dorsum sellae
The dorsum sellae is part of the sphenoid bone in the skull. Together with the basilar part of the occipital bone it forms the clivus.
In the sphenoid bone, the anterior boundary of the sella turcica is completed by two small eminences, one on e ...
, 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
Prenatal development () includes the development of the embryo and of the fetus during a viviparous animal's gestation. Prenatal development starts with fertilization, in the germinal stage of embryonic development, and continues in fetal devel ...
an ossific center appears for each of the
small wings (orbito-sphenoids) just lateral to the
optic foramen
The ''optic foramen'' is the opening to the optic canal. The canal is located in the sphenoid bone; it is bounded medially by the body of the sphenoid and laterally by the lesser wing of the sphenoid.
The superior surface of the sphenoid bone is b ...
; this is followed by the appearance of two nuclei in the
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
The ethmoid bone (; from grc, ἡθμός, hēthmós, sieve) is an unpaired bone in the skull that separates the nasal cavity from the brain. It is located at the roof of the nose, between the two orbits. The cubical bone is lightweight due to a ...
, 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
The greater wing of the sphenoid bone, or alisphenoid, is a bony process of the sphenoid bone; there is one on each side, extending from the side of the body of the sphenoid and curving upward, laterally, and backward.
Structure
The greater wi ...
s). One makes its appearance in each wing between the
foramen rotundum
The foramen rotundum is a circular hole in the sphenoid bone of the skull. It connects the middle cranial fossa and the pterygopalatine fossa. It allows for the passage of the maxillary nerve (V2), a branch of the trigeminal nerve.
Structure
T ...
and
foramen ovale 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 appear, one on either side of the sella turcica, and become blended together about the middle of fetal life.
Each
medial pterygoid plate
The pterygoid processes of the sphenoid (from Greek ''pteryx'', ''pterygos'', "wing"), one on either side, descend perpendicularly from the regions where the body and the greater wings of the sphenoid bone unite.
Each process consists of a me ...
(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 is united to the postsphenoid about the eighth month, and at birth the sphenoid is in three pieces
ig. 4 a central, 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
The ectoderm is one of the three primary germ layers formed in early embryonic development. It is the outermost layer, and is superficial to the mesoderm (the middle layer) and endoderm (the innermost layer). It emerges and originates from t ...
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
Chewing or mastication is the process by which food is crushed and ground by teeth. It is the first step of digestion, and it increases the surface area of foods to allow a more efficient break down by enzymes. During the mastication process, th ...
. 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
The superior orbital fissure is a foramen or cleft of the skull between the lesser and greater wings of the sphenoid bone. It gives passage to multiple structures, including the oculomotor nerve, trochlear nerve, ophthalmic nerve, abducens ner ...
(with
ophthalmic nerve
The ophthalmic nerve (V1) is a sensory nerve of the face. It is one of three divisions of the trigeminal nerve (CN V). It has three branches that provide sensory innervation to the eye, the skin of the upper face, and the skin of the anterior sca ...
),
foramen rotundum
The foramen rotundum is a circular hole in the sphenoid bone of the skull. It connects the middle cranial fossa and the pterygopalatine fossa. It allows for the passage of the maxillary nerve (V2), a branch of the trigeminal nerve.
Structure
T ...
(with
maxillary nerve
In neuroanatomy, the maxillary nerve (V) is one of the three branches or divisions of the trigeminal nerve, the fifth (CN V) cranial nerve. It comprises the principal functions of sensation from the maxilla, nasal cavity, sinuses, the palate a ...
) and
foramen ovale (with
mandibular nerve
In neuroanatomy, the mandibular nerve (V) is the largest of the three divisions of the trigeminal nerve, the fifth cranial nerve (CN V). Unlike the other divisions of the trigeminal nerve (ophthalmic nerve, maxillary nerve) which contain only aff ...
).
Other animals
The sphenoid bone of humans is
homologous with a number of bones that are often separate in other animals, and have a somewhat complex arrangement.
In the early
lobe-finned fish
Sarcopterygii (; ) — sometimes considered synonymous with Crossopterygii () — is a taxon (traditionally a class or subclass) of the bony fishes known as the lobe-finned fishes. The group Tetrapoda, a mostly terrestrial superclass includ ...
es and
tetrapod
Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids (pelycosaurs, extinct theraps ...
s, the pterygoid bones were flat, wing-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. Between the pterygoids lay an elongated, narrow parasphenoid bone, which also spread over some of the lower surface of the braincase, and connected, at its forward end, with a
sphenethmoid bone helping to protect the
olfactory nerve
The olfactory nerve, also known as the first cranial nerve, cranial nerve I, or simply CN I, is a cranial nerve that contains sensory nerve fibers relating to the sense of smell.
The afferent nerve fibers of the olfactory receptor neurons tr ...
s. Finally, the basisphenoid bone formed part of the floor of the braincase and lay immediately above the parasphenoid.
Aside from the loss of the flexible joint at the rear of the palate, this primitive pattern is broadly retained in
reptile
Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates (lizards and snakes) and rhynchocephalians ( ...
s, albeit with some individual modifications. In
bird
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...
s, the epipterygoids are absent and the pterygoids considerably reduced. Living
amphibian
Amphibians are tetrapod, four-limbed and ectothermic vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terres ...
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.
[
In ]mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
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
The greater wing of the sphenoid bone, or alisphenoid, is a bony process of the sphenoid bone; there is one on each side, extending from the side of the body of the sphenoid and curving upward, laterally, and backward.
Structure
The greater wi ...
s when separate in mammals, and form the greater wings of the sphenoid when fused into a larger structure. The sphenethmoid bone forms as three bones: the lesser wings and the anterior part of the base. These two parts of the sphenethmoid may be distinguished as orbitosphenoid
The lesser wings of the sphenoid or orbito-sphenoids are two thin triangular plates, which arise from the upper and anterior parts of the body, and, projecting lateralward, end in sharp points ig. 1
In some animals they remain as separate bones c ...
s and presphenoid, respectively, although there is often some degree of fusion. Only the parasphenoid appears to be entirely absent in mammals.[
In the ]dog
The dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated descendant of the wolf. Also called the domestic dog, it is derived from the extinct Pleistocene wolf, and the modern wolf is the dog's nearest living relative. Do ...
the sphenoid is represented by 8 bones: basisphenoid, alisphenoids, presphenoid, orbitosphenoids, pterygoids. These bones remain separate and are the:
*2 Alisphenoid
The greater wing of the sphenoid bone, or alisphenoid, is a bony process of the sphenoid bone; there is one on each side, extending from the side of the body of the sphenoid and curving upward, laterally, and backward.
Structure
The greater wi ...
s: each greater wing
*2 Orbitosphenoid
The lesser wings of the sphenoid or orbito-sphenoids are two thin triangular plates, which arise from the upper and anterior parts of the body, and, projecting lateralward, end in sharp points ig. 1
In some animals they remain as separate bones c ...
s: each lesser wing
* Basisphenoid: back part of body
* Presphenoid: front part of body
*2 Pterygoids: medial pterygoid plate
Additional images
File:Sphenoid bone - animation.gif, Position of sphenoid bone (shown in green). Animation.
File:Sphenoid bone - inferior view animation.gif, Seen from below (mandible
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...
is removed)
File:Sphenoid bone - superior view animation2.gif, Seen from above (parietal bones
The parietal bones () are two bones in the skull which, when joined at a fibrous joint, form the sides and roof of the cranium. In humans, each bone is roughly quadrilateral in form, and has two surfaces, four borders, and four angles. It is named ...
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
See also
*Sphenoidal sinus
The sphenoid sinus is a paired paranasal sinus occurring within the within the body of the sphenoid bone. It represents one pair of the four paired paranasal sinuses.Illustrated Anatomy of the Head and Neck, Fehrenbach and Herring, Elsevier, 2012, ...
* Pterygospinal ligament
*Basilar skull fracture
A basilar skull fracture is a break of a bone in the base of the skull. Symptoms may include bruising behind the ears, bruising around the eyes, or blood behind the ear drum. A cerebrospinal fluid (CSF) leak occurs in about 20% of cases and m ...
Notes
References
External links
* - "Lateral view of skull."
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Bones of the head and neck