Sphenoid bone

The sphenoid bone (os sphenoidale)is an unpaired bone resembles a bat or a flying insect, which explains the naming of its parts (pterygoid processes – pterygion = wing).

The sphenoid bone has the following parts:

Body of sphenoid (corpus ossis sphenoidalis) is cuboidal in shape. It has an air space inside, called the sphenoid sinus (sinus sphenoidalis).The sinus is divided into two halves by the septum of the sphenoid sinus (septum sinuum sphenoidalium). The body of the sphenoid has six surfaces:

Superior surface has two parts.

The anterior part is the flat upper part with the:

  • Sphenoid jugum (iugum sphenoidale), which is a flat proximal, upper part, related to the gyri recti.
  • Limbus of sphenoid (limbus sphenoidalis).
  • Prechiasmatic groove (sulcus prechiasmaticus) is hollow and is situated between two optic canals. Neurologically it is the place for the optic chiasm.

The posterior part is depressed like a horse saddle and forms the sella turcica (sella turcica)with a central depression for the hypophyseal fossa (fossa hypophysialis). In the front of the posterior part there are:

  • Tuberculum sellae (tuberculum sellae) which projects upwards
  • Middle clinoid process (processus clinoideus medius)
  • Dorsum sellae (dorsum sellae) which is the posterior part of the sella turcica. It projects forward and has posterior Clinoid process (processus clinoideus posterior) on both sides.

Lateral surface has the:

  • Carotid groove (sulcus caroticus) for the internal carotid artery. It is located on both sides of sphenoid body.
  • Sphenoid lingula (lingula sphenoidalis) projects laterally to the artery.

Anterior surface has the:

  • Crest of the sphenoid (crista sphenoidalis) which is part of the superior wall of the nasal cavity. The crest continues down to become a vertical prominence. The sphenoidal crest articulates in the front with the perpendicular plate of the ethmoid bone.
  • Rostrum of the sphenoid (rostrum sphenoidale) which is a part of the nasal septum
  • Sphenoidal concha (concha sphenoidalis) is a paired plate, forming main part of the anterior wall of the sphenoidal sinuses and the roof of the nasal cavity. It is also called sphenoturbinal bone or Bertin’s bone.  In its central part are located the:
  • Apertures of the sphenoidal sinus (aperturae sinus sphenoidalis) which are seen on both sides of the  crest. They open into the sphenoidal sinus, which is an air cavity.

Inferior surface has the:

  • Vaginal process (processus vaginalis) which is a small inferior projection stemming from the inferior wall. It separates the:
  • Palatovaginal canal (canalis palatovaginalis) which is located laterally to the process.
  • Vomerovaginal canal (canalis vomerovaginalis) which is located medially to the process.

Posterior surface together with the basilar part of the occipital bone forms the clivus.

Greater wing (ala maior) is a paired plate located at the lateral sides of the body. Each wing has five surfaces:

Cerebral surface (facies cerebralis) with the:

  • foramen rotundum (foramen rotundum) circular in shape which is located anteriorly to the foramen ovale.
  • foramen ovale (foramen ovale) which is located between the foramen rotundum and spinosum
  • sphenoid spine (spina ossis sphenoidalis) with the:

* foramen spinosum (foramen spinosum) which is the smallest one and it is located posteriorly to the foramen ovale.

Infratemporal surface (facies infratemporalis)has the same features as the cerebral one except the fora- men rotundum. It has the:

  • infratemporal crest (crista infratemporalis), which is the borderline between the temporal and infra- temporal surfaces
  • groove for auditive tube (sulcus tubae auditive) located on the posterior margin of the infratemporal surface

Temporal surface (facies temporalis)with the:

  • zygomatic margin (margo zygomaticus)
  • frontal margin (margo frontalis)
  • parietal margin (margo parietalis)
  • squamous margin (margo squamosa)

Maxillary surface (facies maxillaris)which forms the posterior wall of the pterygopalatine fossa.

Orbital surface (facies orbitalis) which forms the lateral wall of the orbit and separates the superior and inferior orbital fissure (fissura orbitalis superior et inferior).

Lesser wing (ala minor) is a paired, thin triangular plate that arises from the upper and lateral part of the body of the sphenoid bone. The inferior surface forms the roof of the orbit and the upper border of the foramen rotundum. The medial part of the lesser wing forms the anterior clinoid process (processus clinoideus anterior).

Pterygoid processes (processus pterygoideus) descend perpendicularly down uniting the greater wing and the body. Each process consists of the:

  • Medial plate (lamina medialis processus pterygoidei).
  • Lateral plate (lamina lateralis processus pterygoidei) with pterygospinous process.
  • Pterygoid notch (incisura pterygoidea) which is the space located inferiorly between the endings of the medial and lateral plate.
  • Pterygoid fossa (fossa pterygoidea) which is localized above pterygoid notch between the medial and lateral plate. It is a place attachment for the medial pterygoid muscle.
  • Scaphoid fossa (fossa scaphoidea) which is a small hollow in the root of the pterygoid process where the cartilaginous part of auditory tube is localized. Its lateral part is a place for the tensor veli palatini attachment.
  • Pterygoid hamulus (hamulus pterygoideus) which is on the inferior end of medial plate of pterygoid process.
  • Pterygoid canal (canalis pterygoideus) also known as Vidian or Vidius canal pass horizontaly from posterior to anterior through the root of the pterygoid process.
  • Pterygospinous process (procesus pterygospinosus) which is a small process on the posterior margin of  the lateral plate.