Sphenoid Bone

Sphenoid bone anatomy

Sphenoid bone is made up of several projections and features, allowing you to view it in many different ways in the skull.  It consists of only one bone that cuts via the middle sagittal face and facilitates the link between the facial skeleton and the skull.

The body of the sphenoid bone is hollow and is made up of Sphenoid Sinus as well as six projections that are situated in pairs. These are:

  • Lesser Wings, which is a more advanced one.
  • The transitional Greater Wings
  • Pterygoid Processes, which is less accessible than these other two

Lesser wings of sphenoid bone

On the inside of the body, rests Sella Turcica which hosts the pituitary gland.  The Optic Foramen is also housed in the minor lesser wings. The optic nerve goes via it before linking to the eye.

These lesser wings and the transitional greater wings are divided by the Supra-orbital fissure. This can be appropriately observed through the posterior side of every orbit of the two eyes.

Sphenoid Bone Picture


Picture 1 – Sphenoid Bone

Greater wings of sphenoid bone

The greater wings of each side help in the creation of the posterior face that lines the two eye orbits thereby giving rise to the orbital plate. Moreover, the peripheral face of these greater wings may be observed via the side of the skull in a section referred to as Pterion region.

Immediately close to the aforementioned supra orbital fissure and the location of the sphenoid body, the two greater wings are made up of the Foramen Rotundum. This feature spreads the maxillary subdivisions of the cranial, trigeminal or fifth nerve.

Besides these features, the two greater wings consist of a greatly enlarged Foramen Ovale as far as lateral features are taken into account. It helps to spread the mandibular subdivision of this nerve.

Advancing to the posterior end, least enlarged of all the 6 foramena, we encounter the foramen spinosum. This foramenum spreads the central meningial nerves and vessels towards all the brain tissues.

Pterygoid process of the sphenoid bone

The two pterygoid processes extend sparingly from a location close to the connection between the two greater wings and the sphenoid body.

The pterygoid processes are transversely situated next to the posterior segment of nasal opening near the palate. The two processes are created within lateral and medial pterygoid plate.

These two are attached by the corresponding lateral and medial pterygoid plate muscles in the course of life. These two muscles spread from each of these features to join the medial or interior plate of the adjacent mandible found in the gonial region. In the course of life, these muscles facilitate the formation of the crushing action important for the success of the chewing process.

The sphenoid bone is joined by an interconnection of bones. These include Palatines Zygomatic, Temporals, Parietals, Occipital, Frontal, Ethmoid and Vomer Bones

The palatines bone is found on the back side of the nasal passage connecting the pterygoid process and the maxilla.

The zygomatic is also referred to as malar bone or the cheekbone. It consists of pairs that articulate with the frontal bone, temporal bone and maxilla besides the sphenoid bone.

The temporals are located at the base and sides of the cranium. They appear tangential to the temporal cerebrum lobes. The function of the temporal bone is to provide support to the temple which is an area of the face.

When interconnected, the parietal bones outline the crown and the sides of the skull. Every parietal bone consists of 4 angles, 4 borders and 2 faces.

The vomer is one slightly sloping bone found at the center of the sagittal plane. This makes it to articulate appropriately with the vertical face referred to as the ethmoid and the two assists on the creation of the nasal septum. Although it is often deflected little to the right or left the nasal septum is positioned vertically and separates the right and the left nasal openings. Additionally, the vomer mushrooms divide two matching Alae in a dominant manner. Alae articulate and end with the sphenoid bone forming a heart-shaped feature. The vomer is situated on top of both the palatines and the maxillae.

The ethmoid bone consists of several projections and features. However, when compared with the Sphenoid bone it is difficult to observe from various sides of the cranium. It is made up of several plates as well as mutually situated projections

Margins of the sphenoid bone

Going back to the sphenoid bone, that segment of the circular greater wing is uneven and stretches from the bone body towards the back. The medial segment makes the anterior divide of the projection known as foramen lacerum. It shows the end aperture for the entry of the matching artery and nerve.

The lateral segment articulates with the temporal using a synchondrosis. Connecting the two bones is a channel referred to as sulcus tubae. On the front part of the rear side of the bone margin is a hollow with serrated edges. At the end of this wing comes a triangular segment, appropriately situated for the articulation with parietal bone at a sphenoid angle.

The superior plate of the sphenoid bone is flat. Its function is to hold the frontal lobe that extends to the central nervous system. The inferior plate of the sphenoid bone is a part of the crown of the eye orbit and the elevated margin of the orbital fissure, which is a triangular feature that transverses from the cranium cavity to the orbit opening. It is surrounded by the small wing, body and the medial circumference of the orbit plate of the greater wing.

Some of the nerves that it spreads include the abducent nerves, trochlear nerves, and oculomotor nerves. There are 3 segments of the ophthalmic portion that form the trigeminal nerve, a number of filaments that form the cavernous plexus, the orbit segment of the mid-meningeal artery , as well as the recurring section of the lacrimal vessels towards the dura mater. It also consists of the ophthalmic vein.

Borders of the sphenoid bone

The anterior border of the sphenoid bone is jagged to provide easy connection with the frontal bone.

The posterior border of the sphenoid bone is flat and circular and joins into the brain via the lateral tissue. The medial terminal of the posterior border makes the clinoid process of the anterior region. This part provides easy connection to the tentorium cerebelli. Ocasionaly, it is attached to the center clinoid process via a bone spicule. This occurrence leads to the formation if the foramen due to the extinction of the hollow so that the interior carotid artery can be converted ionto the carotico clinoid.

Pictures of Sphenoid Bone
Picture 2 – Sphenoid Bone Image

The smaller wing of the sphenoid bone is attached to the main body via dual roots. The upper root is lean and smooth while the lower one is triangular and thicker. Just occurring in between these roots is an optic foreman, which is responsible for the spread of the ophthalmic artery and optic nerves.

The pterygoid processes slant vertically from the areas where the great wings and the main body join. All the processes comprise of a lateral and medial surfaces while the upper sections are joined at a point that comprises the pterygopalatine a perpendicular and sucus. These two slant to a point of connection.  The surfaces divided underneath by a cleft that is strategically placed at an angle. This gives rise to the pterygoid fissure whose borders are rough so as to offer easy connection with the palatine’s pyramidal process. The dual planes deviate such that they leave a v-shaped fossa behind them this structure is known as the pterygoid fossa and consists of the Tensor veli and the internus. Immediately over this feature is a tiny, oval groove. While the anterior surface of the pterygoid process is wide and triangle-shaped close to its source, it creates a posterior surface and gives the anterior chops known as the pterygoid canal.

The lateral surface of the pterygoid process is wide and thin while its lateral plane is part of the medial surface of the fossa infratemporal. This gives easy articulation surface with the pterygoideus externus. The medal plane creates room for the articulation with the internus.

Presphenoid

Just before childbirth, the ossific position arises for all the small wings immediately laterally with the optic foramen.   The sphenoidal conchae arise from a central location that emerges   nearly the 5th month of the fetal stage of life.

At childbirth, they are made up of tiny triangular-shaped laminae. The actual developement start in the third year when the turn out to be cone-shaped and grooved. It’s in the 12th year that these feature become distinguishable as parts of the sphenoid.

Sphenoid bone in animals

While the human sphenoid bone is similar to several other bones, other animals have sphenoid bones that are frequently divided and have slightly complicated structures.

In the previous species of the tetrapods and lobe fishes, the sphenoid bones had flat and wing-like pterygoid processes being a major section of the mouth crown. Over these pterygoid processes included the epopterygoids that were part of an elastic junction between the palatial area and the braincase in addition to the perpendicular section off bone extending towards the cranial roof. In between these pterygoids, stretched and thin parasphenoids lay there. This bone also extended to some sections of the brain and articulated with a feature known as the sphenethmoid at the front end. This helps to safeguard the olfactory nerves. Lastly, the basisphenoid bone was part of the braincase crown and rested near the parasphenoid.

Apart from the extinction of the flexible junction at the back of the palate, almost all other primitive features are evidenced in reptiles even though there are certain alterations.

When it comes to birds, there are also key modifications. For instance, the pterygoid is greatly minimized while the epipterygoid feature is missing. Amphibians have a comparatively simple cranium. They only consist of a wide parasphenoid being the braincase while the pterygoid processes are comparatively small. Aside from the sphenethmoid, all the other associated bones are missing.

When it comes to mammals, all these variety of bones are frequently connected to form a single network known as the sphenoid. However, this is not the case at all times. The basisphenoid is a key part of the posterior bases whereas the pterygoid processes stands for the pterygoid bones.

The epipterygoids consists of extensions that reach the cranial wall and are known as alisphenoids if they are divisive in the animals and represent the greater wings section of the sphenoid if it is connected to form a large network. The sphenethmoid bone is produced as 3 different bones consisting of the anterior section of the base and the lesser wings. These sections may be separated through the use of the terms presphenoid and orbitoispneoid in that order.


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