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Atlas - Sphenoid bone

The sphenoid bone, also known as the "wasp bone" on account of its shape, makes up most of the base of the skull. It contributes to the floor of the middle cranial fossa and is the most complex bone in the human body.

It is made up of four main parts:
1. The body of the sphenoid bone is the most centrally positioned portion of the bone and houses the sphenoidal sinuses. The sella turcica, the hypophysial fossa and the dorsum sellae are all found on the superior aspect of the body of the sphenoid bone. At the anterior boundary of the sella turcica are two eminences which are the attachment site for the tentorium cerebelli, known as the anterior clinoid processes. While on the posterior boundary of the dorsum sellae are the posterior clinoid processes to which the tentorium cerebelli also attaches.

2. The lesser wings of the sphenoid bone, which participates in the formation of the lateral margin of the orbit inferiorly, contains the optic canal through which the optic nerve (CN II) and ophthalmic artery are transmitted.

3. The greater wings of the sphenoid bone contain foramen rotundum which transmits the maxillary nerve (CN V2), foramen ovale which transmits the mandibular nerve (CN V3) and the accessory meningeal artery, and foramen spinosum which transmits the middle meningeal vessels and the spinous nerve. The greater wings have a zygomatic margin, a parietal margin and squamous margin. In addition, it also has a cerebral surface, a maxillary surface, an orbital surface and a temporal surface.

4. The pterygoid processes, which are basically extensions of the base of the body of the sphenoid bone, contain the pterygoid canal, the palatovaginal canal and the pterygoid hamulus. They are also composed of a medial plate and a lateral plate.

Other structures of the sphenoid bone include, the sphenoidal conchae, the infratemporal crest, the sphenoidal crest, the pterygoid fissure, the pterygoid and sphenoidal fossae, the sphenoidal rostrum, spine of the sphenoid bone, the carotid sulcus and the sulcus of the auditory tube.

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