Sphenoid bone

The sphenoid bone (os sphenoidale) occupies a central position at the base of the skull. It participates in the formation of the base of the skull, its lateral sections and a number of cavities and pits. In the sphenoid bone, the body, pterygoid processes, large and small wings are distinguished.

The body of the sphenoid bone (corpus sphenoidale) has an irregular shape and six surfaces: the upper, lower, posterior, fused (in an adult) with the basilar part of the occipital bone, anterior and two lateral surfaces. On the upper surface of the body there is a depression - the Turkish saddle (sella turcica) with a deep pituitary fossa (fossa hypophysialis). Back in the Turkish saddle, the back of the saddle (dorsum sellae) is distinguished, and in the front is the tuberculum of the saddle (tuberculum sellae). On either side of the body of the bone, a carotid sulcus (sulcus caroticus) is visible - the trail of the inner carotid artery. On the front surface of the body of the sphenoid bone there is a wedge-shaped crest (crista sphenoidalis). On the sides of the ridge are irregularly shaped wedge-shaped conchae (conchae sphenoidales), bounding the apertures of the sphenoid sinus. The sinus sphenoidalis (sinus sphenoidalis) is an air-filled cavity that communicates with the nasal cavity.

The lateral surfaces of the body of the sphenoid bone are directly transformed into paired small and large wings.

The small wing (ala minor) is a directed laterally flattened bone plate, at the base of which there is a visual canal (canalis opticus) leading to the orbit. The posterior free margin serves as a boundary between the anterior and posterior cranial fossae. The anterior margin joins the orbital part of the frontal bone and the trellis plate of the trellis. Between the small wing at the top and the upper edge of the large wing is an elongated hole - the upper orbital fissure (fissura orbitalis superior), which connects the cranial cavity with the orbit.

The large wing (ala major) starts from the lateral surface of the body of the sphenoid bone with a wide base and, like the small wing, is directed laterally. It has four surfaces: the cerebral, ophthalmic, temporal and maxillary. The concave medulla is turned into the cavity of the skull. It has three holes through which blood vessels and nerves pass. A round hole (foramen rotundum), located closer to the base of the large wing, leads to the pterygoid palatine fossa. At the middle of the wing there is an oval foramen ovale opening on the base of the skull, and behind it is a small spinous foramen (foramen spinosum). The facial surface (facies orbitalis) is smooth, participates in the formation of the orbital wall of the orbit. On the temporal surface {facies temporalis) there passes the trailing crest (crista infratemporalis), oriented in the anteroposterior direction and delimiting the temporal fossa from the transverse on the lateral surface of the skull.

The maxillary surface (facies maxillaris) faces forward - into the pterygo-palatine fossa.

The pterygoid processus (processus pterygoideus) is paired, moving downward from the body of the sphenoid bone. In the process, the medial and lateral plates (lamina medialis et lamina lateralis) are isolated. Behind between the plates is the pterygoid fossa (fossa pterygoidea). At the base of the pterygoid process, a narrow winglike (canalis) canalis (canalis pterygoideus) in front of it, which connects the pterygoid-palatine fossa on the whole skull to the region of the lacerated hole, lies ahead.

The occipital bone (os occipitale) is located in the posterior part of the brain area of the skull. In this bone, the basilar part, the two lateral parts and the occipital scales, which surround the large (occipital) foramen (foramen magnum), are distinguished.

The basilar part (pars basilaris) lies in front of the large (occipital) opening. From the front, it joins the body of the sphenoid bone, together with which it forms a clavus. On the lower surface of the basilar part there is an elevation - pharyngeal tuberculum (tuberculum pharyngeum), and along the lateral margin there is a furrow of the lower stony sinus (sulcus sinus petrosi inferioris).

The lateral part (pars lateralis) is paired, behind it passes into the scales of the occipital bone. Bottom on each lateral part there is an ellipsoidal elevation - the occipital condyle (condylus occipitalis), at the base of which is the canalis nerve hypoglossi canal. Behind the condyle is a condylar fossa (fossa condylaris), and on its bottom - a condylar canal opening (canalis condylaris). On the side of the occipital condyle is the jugular incision (incisura jugularis), which, together with the jugular cutting of the pyramid of the temporal bone, forms a jugular opening. Next to the jugular notch on the cerebral surface is a sigmoid sinus groove (sulcus sinus sigmoidei).

Occipital scales (squama occipitalis) - wide, convex to the outside plate, the edges of which are strongly jagged. On the whole skull they connect with the parietal and temporal bones. In the center of the external surface of the scales, the external occipital protrusion (protuberantia occipitalis externa) is visible, from which a slightly outlined upper line (linea nuchae superior) departs in both directions. Down from the ledge to the large (occipital) opening, the external occipital crest (crista occipitalis externa) passes. From its middle, to the right and to the left, is the lower, different line (hinea nuchae inferior). Over the outer occipital protrusion, the highest line (linea nuchae suprema) is sometimes seen.

On the inner side of the occipital scales is a cruciform elevation (eminentia cruciformis), dividing the cerebral surface of the scales into 4 pits. The center of the cruciform elevation forms the internal occipital protrusion (protuberantia occipitalis interna). To the right and to the left of this projection there is a furrow of the transverse sinus (sulcus sinus transversus). Upward from the protrusion there is a furrow of the superior sagittal sinus (sulcus sinus sagittalis superioris), and downward, to the large (occipital) opening, is the internal occipital crest (crista occipitalis interna).

[1], [2], [3], [4], [5]