The Sphenoid bone of Ox is placed at the base of the skull. In the calf at birth and some months after it consists of two pieces.
The posterior part lies next to the basilar part of the occipital, being termed post-sphenoid and the anterior part pre-sphenoid. Though the two parts fuse later in life it is convenient to describe them separately.
Post-sphenoid
The post-sphenoid has a body, two temporal wings and two pterygoid (subsphenoidal)processes.
The external face of the bodypresents close to its junction with the pterygoid avidian groove for the nerve of the pterygoid canal (vidian nerve).
The internal surface presents the hypophyseal or pituitary fossa (sella turcica) for the pituitary gland. The dorsum sellae is a transverse projection at the posterior end of the body and bears posterior clinoid processes.
The wings diverge outward from the body.
Each is perforated about its middle by foramen ovale for the mandibular nerve and middle meningeal artery.
The internal surface presents a longitudinal groove leading to foramen orbito rotundum.
The posterior borderforms the anterior margin of the foramen lacerum.
The anterior border presents a notch medially which with a similar one on the wing of pre-sphenoid forms the foramen orbito-rotundum for III, IV, VI cranial nerves and maxillary and ophthalmic division of V cranial nerves.
It is free antero-laterally to form the pterygoid crest.
The subspheniodal or pterygoid processes spring from the anterior part of the wing and is directed downward and forward.
It’s medial face is covered by the pterygoid and the palatine bones.
Pre-sphenoid
The pre-sphenoidlies at a higher level, has a body and two orbital wings.
The anterior part of the external face of the body is concealed mostly by the vomer and laterally by the pterygoid bones.
The vidian groove is continued by a vidian canal at the junction of the wing with the body and opens into the pterygo-palatine fossa.
The cranial surface of the body presents anteriorly a median ethmoid spine, which joins the crista galli of the ethmoid. Posteriorly and at a lower level is the optic groove which supports the optic commissure in life and the groove on either side leads to the optic foramen.
In the adult, the body of pre-sphenoid is slightly excavated to form the sphenoidal sinus.
The orbital wings are larger than the temporal wings.
They curve dorsolaterally from the sides of the body.
External surface forms a part of the orbital wall. It is overlapped by the frontal in such a manner that it appears to divide into two branches.
The anterior one of these joins the ethmoid and perpendicular part of palatine at the spheno-palatine foramen. At its junction with the body it is pierced by the optic foramen.
The posterior border forms with the wings of post-sphenoid, the foramen orbito-rotundum. The internal face lodges the cerebrum.
Horse
The posterior border of the wing of the post-sphenoid forms the anterior border of foramen lacerum and presents three notches –carotid, oval and spinous from within outward.
The foramen lacerum is a large triangular gap in the dry skull and is largely closed in life by dense fibrous tissue with a posterior opening i.e. foramen lacerum posterius or jugular foramen for the IX, X and XI cranial nerves and anteriorly the notches referred to above are converted into the carotid artery, mandibular nerve and the middle meningeal artery respectively.
The dorsum sellae and post clinoid processes are absent.
The anterior border of the wing meets the wings of pre-sphenoid above and below it, free and forms the pterygoid crest, which is continued on the pterygoid process.
On or under the upper part of the crest there is usually a small trochlear parvum, which communicates with the alar canal.
The wing presents close to its anterior border the foramen rotundum (for the maxillary division of V cranial nerve) and with the pre-sphenoid wing, it forms the foramen orbitale which is separated from the foramen rotundum by a thin plate of bone.
The foramen orbitale serves for the passage of III, VI cranial and ophthalmic division of V cranial nerves.
The pterygoid processes project downward and forward and curve outward at its lower part. The root of the process is perforated by alar (subsphenoidal) canal for the passage of the internal maxillary artery.
The wingsof pre-sphenoid form the foramen orbitale with the wing of post-sphenoid. In front and above this is the optic foramen. Anteriorly, the wings meet the cribriform plate of ethmoid and orbital plates of frontal to form the ethmoidal foramen. The sphenoidal sinus in the body of pre-sphenoid communicates with the palatine sinus in the vertical part of palatine bone.
Dog
The body of both pre and post sphenoid is dorsoventrally flattened. Dorsum sellae and posterior clinoid processes are better developed.
Anterior clinoid processes project from the roots of the orbital wings.
Temporal wings are extensive and articulate with the parietals dorsally.
Foramen orbitale is at the junction of the wings a little lower to the optic foramen.
An alar canal is present and the foramen rotundum opens into it.
Foramen ovale is as in the ox.
The carotid notch with a similar notch on the temporal forms the carotid from the foramen.
The sphenoidal sinus is absent.
Fowl
The sphenoid is concealed largely by a large triangular basitemporal or sub-sphenoid bone.
