Sphenoid Bone Markings.
The sphenoid bone (os sphenoidale; Gr., sphen - wedge + eidos - form) is a butterfly-shaped cranial bone that is located in the middle of the skull between the frontal and temporal bones.
It primarily consists of a centrally positioned body, which surrounds and protects the pituitary gland, and two sets of lateral, wing-like extensions called the greater and lesser wings.
A pair of pterygoid processes (processus pterygoideus) extend from inferior surface of the sphenoid bone, near the junction of the body and greater wings. They provide attachment for some of the chewing and swallowing muscles.
a. Body (corpus sphenoidalis) is the cuboid-shape center portion of the sphenoid bone. It contains the sphenoid sinuses and a large despression for the pituitary gland.
Lesser wing (ala minor sphenoidalis) is the smaller of two wing-like lateral extensions that arise from the sides of the sphenoid body. The lesser wings are flattened, triangular in shape, and located above and anterior to the greater wings.
c. Greater wing (ala major sphenoidalis) is the larger of two wing-like lateral extensions that arise from the sides of the sphenoid body. The greater wings curve upward, laterally, and backwards to form a portion of the prominent middle cranial fossa.
d. Orbital surface of the greater wing (facies orbitalis sphenoidalis) is the smooth, anterior portion the greater wing. It is quadrilateral-shaped (four sides) and forms a portion of the posterior wall of the orbit.
e. Optic canal or foramen (canalis opticus or foramen opticum sphenoidalis) is an opening in the lesser wing that transmits the optic nerve and ophthalmic artery.
f. Superior orbital fissure (Fissura orbitalis superior sphenoidalis) is an narrow opening between the lesser and greater wings in the posterior orbit. It transmits the oculomotor, trochlear, trigeminal, and abducen nerves.
g. Foramen rotundum (foramen ovale sphenoidalis) is a round hole in the antero-medial portion of the greater wing. It gives passage to the maxillary nerve branch of the trigeminal nerve.
h. Foramen ovale (foramen ovale sphenoidalis) is an oval hole in posterior portion of the greater wing. It is the passageway for the mandibular nerve (branch of the trigeminal nerve), accessory meningeal artery, lesser petrosal nerve, and emissary veins.
i. Foramen spinosum (foramen spinosum sphenoidalis) is a small opening posterior to the foramen ovale that transmits the middle meningeal artery and the meningeal branch of the mandibular nerve.
j. Chiasmatic groove or sulcus (sulcus chiasmaticus or sulcus prechiasmaticus sphenoidalis) is a narrow, transverse depression that runs between the optic canals. The optic nerves pass along this groove before they partially decussate (cross or intersect) at the optic chiasm.
k. Anterior clinoid process (processus clinoideus anterior sphenoidalis) is a pos-terior projection from each lesser wing. They are attachment sites for the tentorium cerebelli (dura mater), which separates the cerebellum from the inferior occipital lobes of the brain. The processes also help enclose and protect the pituitary gland.
l. Sella turcica (sella turcica sphenoidalis; L. Turkish saddle) is a depression on the upper part of the body. It houses the pituitary gland (hypophysis) and consists of the hy-pophyseal fossa, dorsum sellae, tuberculum sellae, and posterior clinoid processes.
m. Hypophyseal fossa (fossa hypophysialis sphenoidalis) is the depression in which the pituitary gland sits.
n. Tuberculum sellae (tuberculum sellae sphenoidalis) is the raised anterior edge of the sella turcica, which is located just posterior the chiasmatic groove.
o. Dorsum sellae( dorsum sallae sphenoidalis) is the square-shaped posterior wall of the sella turcica.
p. Posterior clinoid process (processus clinoideus posterior sphenoidalis) is a small, lateral extension from each side of the dorsum sellae. The left and right clinoid processes help enclose the posterior wall of the sella turcica around the pituitary gland and give attachment to the tentorium cerebelli region of the dura mater.
q. Pterygoid process (processus pterygoideus sphenoidalis) is an inferior extension from the junction of the sphenoid body and greater wing. Each pterygoid process consists of two, thin, vertical plates (Gr., pterygodes - wing shaped). The plates are fused anteriorly and separated by a cleft posteriorly.
r. Lateral pterygoid plate (lamina lateralis processus pterygoidei sphenoidalis) is the lateral of two plates that form the pterygoid proces. It is the attachment point for the lateral and medial pterygoid muscles, which move the mandible while chewing.
s. Medial pterygoid plate (lamina medialis processus pterygoidei sphenoidalis) is the narrower, longer plate of pterygoid process. Its medial surface gives support to the posterior opening of the nasal cavity.
t. Pterygoid hamulus (hamulus pterygoideus sphenoidalis) is a hook-like inferior extension of the medial pterygoid plate. The hamulus acts like a pulley for the gliding movements of the tendon for the tensor veli palatini muscle. This muscle tenses or elevates the soft palate during the swallowing procees so food does not enter the nasopharynx.