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Sphenoid bone

German: Os sphenoidale

1 Definition

The sphenoid bone is a skull bone, which is located at the skull base frontal to the two temporal bones and the occipital bone. From dorsal perspective, it has the form of a butterfly with the body (corpus ossis sphenoidalis), two wings (major and minor alae) radiating laterally, and the pterygoid processes radiating caudally.

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2 Corpus ossis sphenoidalis (body of the sphenoid bone)

The body of the sphenoid bone has a more or less square base. In its interior, you can find two cavities separated by a septum, the sphenoidal sinuses.

2.1 Facies superior

From ventral-to-dorsal perspective, the superior surface of the body of the shpenoid bone shows a number of important anatomical structures:

2.2 Facies laterales

Both lateral surfaces of the body off the sphenoid bone are the origin of the two greater wings of the sphenoid bone (Alae majores). Directly above their insertion, there is a s-curved groove (carotid sulcus), which accommodates the internal carotid artery and the cavernosus sinus. It is laterally delimitated from the wing by a bony crest, the lingula.

2.3 Facies posterior

The posterior surface of the body of the sphenoid bone articulates with the occipital bone. During childhood, this connection is formed by a cartilage plate, which ossificates between the 18th and 25th year of life.

2.4 Facies anterior

The front surface of the body of the sphenoid bone shows a bony crest in the middle, the sphenoidal crest, which articulates with the perpendicular lamina of the ethmoid bone and forms a part of the nasal septum. Further parts of the front surface articulate with the ethmoid bone, the frontal bone and the palatine bone. On both sides, irregularly shaped openings lead into the sphenoidal sinuses. They are both shaped highly individual and can be further divided by small bony septums. Ventrally, they communicate with the superior and posterior nasal cavity and are partly closed by the sphenoidal conchae.

2.5 Facies inferior

On the inferior surface of the body of the sphenoid bone, a triangular bony crest called rostrum of the sphenoid is protruding. It continues the sphenoidal crest in dorsal direction and caudally enters into an articulation with the vomer via the perpendicular lamina of the ethmoid bone, and thus forms the bony nasal septum.

3 Alae ossis sphenoidalis (wings of the sphenoid bone)

The wings of the sphenoid bone are planar paired bone processes of the sphenoid bone. One can differentiate between:

The greater wings of the sphenoid bone are two sturdy bone processes on both sides of the body of the sphenoid bone. They are concavely curved towards cranial direction. Its posterior part articulates with the angle between the petrosal part of the temporal bone and the squamous part of the temporal bone (squama ossis temporalis). On its backside, you can see a prominent bone crest pointing below, the angular spine, where the sphenomandibular ligament inserts and the tensor veli palatini muscle has its origin.

The lesser wings of the sphenoid bone are two thin, triangular bone plates that insert up front at the body of the sphenoid. They draw to the lateral side and end in a sharply terminating tip.

4 Pterygoid process (wing process)

The pterygoid process originates at the connection between the body of the sphenoid bone and its greater wing on both sides. It points in caudal direction like a pendulum.

The pterygoid process consists of two bone lamellas, the medial and lateral lamina. Both its superior part fuse on the anterior face and form the posterior wall of the pterygopalatine fossa, which contains the pterygoid canal. Caudally, it continues as a vertically running bone canal, the greater palatine groove.

In posterior direction, the two lamella are diverging and enclose a v-shaped bony hollow, the pterygoid fossa, which accommodates the medial pterygoid muscle and the tensor veli palatini muscle. Above the fossa, you can find a small, flat and oval hollow, the scaphoid fossa. It is the origin of the tensor veli palatini muscle.

Further caudally, both lamella are separated by an extensive cleft, the pterygoid fissure. The edges of the fissure are rough, since the pterygoid process articulates here with the pyramidal process of the palatine bone.

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Specialties: Anatomy

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