Sphenoid bone

The sphenoid ( sphenoid ) is one of the bones of the cranium. It is located relatively deep in the middle cranial area. It forms the rear of the eye socket (orbit ) and together with the occipital bone of the skull base.

The name of the sphenoid bone ( v. greek sphenoid ) is probably caused by the typo of a monk in the Middle Ages. By Os was from the sphenoid bone sphekoidale (Greek wasp leg). The sphenoid looks with its wings more like a wasp than a wedge.

History of development

Developmentally, arises the sphenoid bone of two, the front and rear of the sphenoid ( basisphenoid and Präsphenoid ). Both parts merge but in humans before birth. In many other mammals can be both, by a cartilage connection ( synchondrosis ) differ significantly associated units to the juvenile animal yet. Only in the adult animal they merge bony ( synostosis ).

Both cuneiform bones are similar in their structure nor a vortex (especially the Atlas ) and arise, in contrast to most other cranial bones, from a cartilaginous precursor by endochondral ossification. Both have run out a body ( corpus ) of the two wing- like extensions ( alae ).

Outdoor relief

The wings on both sides of the anterior sphenoid (ala parva or Ala ossis praesphenoidalis, in humans Ala minor) in humans are relatively small, more expansive and most other animals and form a large part of the posterior orbit. They are each pierced by the optic canal, which serves for the passage of the optic nerve ( optic nerve ). In humans, they run medially and behind each in an appendix, the anterior clinoid process, from. These extensions which belongs to the dura mater cerebellum tent ( tentorium cerebelli ) is attached.

The two wings of the posterior sphenoid (ala magna or Ala ossis basisphenoidalis, human sphenoid ), however, are relatively large in humans. In each wing is pierced by the foramen ovale, the mandibular nerve (one of the three main branches of the 5th cranial nerve ) is the nerve to the exit. In some animals, the foramen ovale is a cut ( notch ovalis ) a larger hole ( foramen lacerum ) at the skull base. In man also the foramen rotundum is in great wing of the sphenoid delineated. It contains the maxillary nerve (another main branch of the 5th cranial nerve ). At the far end of the great wing of the sphenoid foramen spinosum is that the entry of the middle meningeal artery is used in the cranial cavity in humans, horses and dogs.

Between the two wings of the sphenoid bone in primates a relatively large, slit-like opening, the superior orbital fissure remains open, simply and most other mammals as orbital fissure. Through this opening, get some cranial nerves in the eye socket ( oculomotor nerve, nervus abducens, trochlear, ophthalmic nerve ). In the even-toed ungulates orbital fissure merges with the foramen rotundum foramen orbitorotundum and serves as in humans the foramen rotundum to the passage of the maxillary nerve.

From the body of the sphenoid rear springs after rostroventral the wing extension ( pterygoid process, see figure at right). This limited together with the palatine bone the posterior nares. Medial to the wing extension is in most mammals but not in humans, the small clasp-like wing bone (os pterygoideum ). The origin of the pterygoid process is pierced by a thin channel in the longitudinal direction. This pterygoid canal serves for the passage of the nerve of the pterygoid canal ( VIDI nerve) to the pterygopalatine fossa (wing - palate - pit). In dogs and horses of the pterygoid process is still characterized by a larger longitudinal channel. This canal serves alaris the passage of the maxillary artery.

Internal relief

The wings of the posterior sphenoid (ala magna or Ala ossis basiphenoidalis ) form the middle cranial fossa ( fossa media), located in the central and mid-brain.

The body of the sphenoid bone forms the back skull cave side, a saddle-shaped structure, which is referred to as Turks saddle ( sella turcica ). Turks this saddle is characterized by a central hole, in the pituitary gland and which is therefore as Hypophysengrube ( pituitary fossa ) is referred to. The pit is covered by a removal of the dura mater, the diaphragm sellae, pituitary and brain which separates and is pierced only by their connection, the pituitary stalk.

Before the Turks saddle a groove is for the crossing of the optic nerve ( optic chiasm ), which is called the sulcus chiasmatis.

Sphenoid sinus

In the body of the anterior sphenoid bone in humans and some animal species the cancellous bone ( diploe ) is replaced by a ballooning of the nasal cavity. This sinus is called the sphenoid sinus ( sphenoidal sinus ).

Literature and sources

F.-V. Salomon: Boney skeleton. In: Salomon, F.-V. et al (eds): Anatomy for veterinary medicine. Enke Verlag, Stuttgart 2004, ISBN 3-8304-1007-7, pp. 37-110.
J. Fanghänel (ed.): Waldeyer human anatomy. de Gruyter 2003, 17th edition, ISBN 3-11-016561-9, pp. 192-195.

Skull: occipital bone | sphenoid | parietal | ethmoid | prefrontal

Nasal bone Posterior nasal apertures

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