Sphenoid bone

Os sphenoideum

The unpaired, butterfly-shaped bone across the centre of the skull base, linking the braincase to the face and cradling the pituitary gland.

At a glance

English: Sphenoid bone
Latin (TA2): Os sphenoideum
System: Bone
Region: Head
Side: Single, on the midline
Muscles on it: Temporalis

About the sphenoid bone

The sphenoid lies across the middle of the skull base, wedged between the frontal and ethmoid bones in front and the occipital and temporal bones behind. Seen from in front it looks like a butterfly or bat with spread wings. It has a cube-shaped central body, a greater wing sweeping out from each side, a lesser wing from the top of the front, and a pterygoid process hanging down from each side below. Its neighbours are the occipital, temporal, parietal and frontal bones of the braincase and the ethmoid, zygomatic, palatine and vomer of the face, so it ties the cranium to the facial skeleton.

The body is hollowed by the two sphenoidal sinuses, separated by a septum. On its upper surface, from front to back, lie the flat sphenoidal yoke, the chiasmatic sulcus, the tuberculum sellae and the saddle-like sella turcica, whose deep hypophysial fossa holds the pituitary gland; the dorsum sellae closes it behind and slopes into the clivus. Along each side a groove carries the internal carotid artery through the cavernous sinus. In front, the sphenoidal crest meets the ethmoid's perpendicular plate within the nasal septum.

Each lesser wing is a thin triangle that floors part of the anterior cranial fossa and ends medially in the anterior clinoid process; the optic canal passes through its root, and the superior orbital fissure opens between it and the greater wing. The greater wing floors the middle cranial fossa and is pierced in a curve by the foramen rotundum, foramen ovale and foramen spinosum, for the maxillary nerve, the mandibular nerve and the middle meningeal artery. Its other faces form the back of the lateral orbital wall and parts of the temporal and infratemporal fossae. Each pterygoid process has a medial and a lateral plate with the pterygoid fossa between them.

Most of the bone forms in cartilage. At birth it consists of three separate pieces: a central body with the lesser wings and two side pieces of greater wing and pterygoid process, which join during the first year; the body fuses with the occipital bone by about the twenty-fifth year. Clinically, surgeons reach the pituitary through the nose and the sphenoidal sinus. A pituitary tumour can enlarge the sella and press upward on the optic chiasm, typically narrowing the outer halves of both visual fields.

Function and supply

Function: Forms the central floor of the cranium and parts of the orbits and temporal fossae, carries the main nerves and vessels of the orbit and face through its openings, and anchors the pterygoid muscles and part of temporalis for chewing.
Nerve supply: Not supplied as a muscle is; the optic, oculomotor, trochlear and abducens nerves and all three divisions of the trigeminal nerve pass through its canals, fissure and foramina, and trigeminal meningeal branches supply the dura on it.
Blood supply: Branches of the maxillary artery, including the middle meningeal and deep temporal arteries, supply its outer surfaces, and small branches of the internal carotid artery supply the bone around the sella.

Parts of the sphenoid bone

Each number is marked on the model. Press one, here or on the model, to see it named in place.

Anterior clinoid processProcessus clinoideus anteriorThe rounded backward point at the inner end of each lesser wing, overhanging the sella turcica. The free edge of the tentorium cerebelli is fixed to it, and the internal carotid artery turns upward just beside it.
Body of sphenoid boneCorpus ossis sphenoideiThe central, roughly cube-shaped part of the bone. It is hollowed by the two sphenoidal sinuses and carries the sella turcica on its upper surface.
Carotid sulcusSulcus carotidisA curved groove along each side of the body, above the root of the greater wing. It carries the internal carotid artery as it runs through the cavernous sinus.
Cerebral surface of greater wingFacies cerebralis alae majorisThe deeply hollowed upper face of each greater wing, which makes up the front and much of the base of the middle cranial fossa. The temporal lobe moulds it, and the foramina rotundum, ovale and spinosum pierce it.
Chiasmatic sulcusSulcus chiasmaticusA narrow groove running across the upper body between the two optic canals, just in front of the tuberculum sellae. Despite its name the optic chiasm usually lies above and behind it rather than in it.
Dorsum sellaeThe square plate of bone that forms the back wall of the sella turcica. Its upper corners make the posterior clinoid processes, and its back slopes down into the clivus with the basilar occipital.
Foramen ovaleA large oval hole near the back of the greater wing, behind and outside the foramen rotundum. It carries the mandibular nerve, the accessory meningeal artery and often an emissary vein down to the infratemporal fossa.
Foramen rotundumA round hole near the root of the greater wing, leading forward from the middle cranial fossa into the pterygopalatine fossa. The maxillary nerve passes through it.
Foramen spinosumA small round hole behind and outside the foramen ovale, just in front of the sphenoidal spine. The middle meningeal artery enters the skull through it, with a meningeal branch of the mandibular nerve.
Frontal margin of greater wingMargo frontalis alae majorisThe rough, triangular upper front edge of the greater wing. It meets the frontal bone at the sphenofrontal suture.
Greater wingAla majorThe broad curved plate that extends outward and upward from each side of the body. It helps form the middle cranial fossa, the outer wall of the orbit and the temporal and infratemporal fossae.
Groove of pterygoid hamulusSulcus hamuli pterygoideiA smooth groove on the outer side of the hamulus at the lower end of the medial pterygoid plate. The tendon of tensor veli palatini turns around it on its way into the soft palate.
Hypophysial fossaFossa hypophysialisThe deepest part of the sella turcica, between the tuberculum sellae in front and the dorsum sellae behind. It holds the pituitary gland, and its enlargement on imaging can be the first sign of a pituitary tumour.
Infratemporal surface of greater wingFacies infratemporalis alae majorisThe lower part of the outer face of the greater wing, below the infratemporal crest. It roofs the infratemporal fossa, is pierced by the foramina ovale and spinosum, and gives origin to the upper head of lateral pterygoid.
Lateral pterygoid plateLamina lateralis processus pterygoideiThe broad, thin outer plate of the pterygoid process, turned slightly outward. Its outer face gives origin to the lower head of lateral pterygoid and its inner face to the deep head of medial pterygoid.
Lesser wingAla minorThe thin triangular plate that projects sideways from the upper front of the body to a sharp tip. Its upper surface helps floor the anterior cranial fossa, its lower edge borders the superior orbital fissure and its root surrounds the optic canal.
Limbus of sphenoidLimbus sphenoideusThe ridge along the back edge of the sphenoidal yoke, in front of the chiasmatic sulcus. It runs out on each side towards the anterior clinoid process.
Maxillary surface of greater wingFacies maxillaris alae majorisA small area at the front of the root of the greater wing that faces into the pterygopalatine fossa, towards the maxilla. The foramen rotundum opens on it.
Medial pterygoid plateLamina medialis processus pterygoideiThe narrower inner plate of the pterygoid process, forming the side wall at the back of the nasal cavity. It ends below in the pterygoid hamulus, and the superior constrictor of the pharynx attaches along its lower edge.
Optic canalCanalis opticusThe short channel between the body and the two roots of the lesser wing, leading from the middle cranial fossa into the orbit. It carries the optic nerve and the ophthalmic artery.
Orbital surface of greater wingFacies orbitalis alae majorisThe smooth, four-sided face turned forward and inward, making the rear of the orbit's outer wall. It borders both the superior and inferior orbital fissures.
Parietal margin of greater wingMargo parietalis alae majorisThe top tip of the greater wing. It meets the sphenoidal angle of the parietal bone at the pterion.
Posterior clinoid processProcessus clinoideus posteriorA small knob at each upper corner of the dorsum sellae. The attached edge of the tentorium cerebelli is fixed to it.
Pterygoid canalCanalis pterygoideusA narrow tunnel through the root of the pterygoid process, running from near the foramen lacerum forward into the pterygopalatine fossa. It carries the nerve of the pterygoid canal, formed by the greater and deep petrosal nerves, with a small artery.
Pterygoid fossaFossa pterygoideaThe hollow at the back between the diverging medial and lateral pterygoid plates. The deep head of medial pterygoid arises from it.
Pterygoid hamulusHamulus pterygoideusThe small hook at the lower tip of the medial pterygoid plate. The tendon of tensor veli palatini turns round it, and the pterygomandibular raphe is fixed to its tip.
Pterygoid notchIncisura pterygoideaThe gap between the lower ends of the medial and lateral pterygoid plates. The palatine bone's pyramidal process fits into it.
Pterygospinous processProcessus pterygospinosusA sharp spur projecting backward from the lateral pterygoid plate. A ligament runs from it to the sphenoidal spine and sometimes turns to bone, which can trap branches of the mandibular nerve.
Scaphoid fossaFossa scaphoideaA small, shallow, boat-shaped dip above the pterygoid fossa at the top of the medial plate. Part of tensor veli palatini arises from it.
Sella turcicaThe saddle-shaped hollow on the upper surface of the body, named after a Turkish saddle. It comprises the tuberculum sellae in front, the hypophysial fossa in the middle and the dorsum sellae behind.
Sphenoidal crestCrista sphenoideaA thin vertical ridge down the middle of the front of the body. It meets the ethmoid's perpendicular plate and forms a small part of the nasal septum.
Sphenoidal lingulaLingula sphenoideaA small tongue of bone at the back of the carotid groove, in the angle between body and greater wing. It overhangs the start of the groove where the internal carotid artery enters the cranial cavity.
Sphenoidal yokeJugum sphenoideumThe smooth, flat plate on top of the front of the body that joins the two lesser wings. It helps floor the anterior cranial fossa, in front of the optic groove.
Spine of sphenoid boneSpina ossis sphenoideiA downward spike at the back corner of each greater wing, behind the foramen spinosum. The sphenomandibular ligament and some fibres of tensor veli palatini attach to it.
Squamosal margin of greater wingMargo squamosus alae majorisThe back edge of the greater wing. It meets the squamous part of the temporal bone at the sphenosquamosal suture.
Sulcus of auditory tubeSulcus tubae auditivaeA groove on the underside of the skull base between the back edge of the greater wing and the petrous temporal bone. It lodges the cartilaginous part of the auditory tube, which runs from the middle ear to the nasopharynx.
Temporal surface of greater wingFacies temporalis alae majorisThe upper part of the outer face of the greater wing, above the infratemporal crest. It lines part of the temporal fossa, where fibres of temporalis arise from it.
Tuberculum sellaeA small rise behind the chiasmatic sulcus, forming the front edge of the sella turcica. Small middle clinoid processes may project from its ends.
Vaginal process of sphenoid boneProcessus vaginalis ossis sphenoideiA thin plate projecting inward from the root of the medial pterygoid plate, under the body. It meets the vomer and the palatine bone and helps form the small palatovaginal canal.
Zygomatic margin of greater wingMargo zygomaticus alae majorisThe front edge of the greater wing, in the orbit's lateral wall. It meets the zygomatic bone.

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At a glance

About the sphenoid bone

Function and supply

Related structures

See the sphenoid bone where it really sits, with every layer of the body around it.