Sphenoid (bone)

by Abdullah Arif · June 13, 2024

Sphenoid . It is an odd, central and symmetrical bone, which occupies the anterior and middle part of the base of the bone cavity . It is located between the ethmoid and the frontal , which are in front, and the occipital , which is behind.

At first glance, the sphenoid appears as a very complex bone. As a whole, the sphenoid is composed of a cubic-shaped body, two minor wings attached to the upper part of the body, two major wings attached to the lateral surfaces of the body, two pterygoid processes as landing gear and two hooks, for example. behind these.

Summary

[ disguise ]

1 Body
2 Minor wings
3 Greater wings
4 Pterygoid process
5 Sources

Body

It has a cubic shape and shows two cavities (like front windows of the spacecraft), the sphenoidal sinuses, separated by a median septum (sphenoidal intersinusal septum). This septum tapers forward to form the sphenoidal crest (like the prow of the spaceship) which is extended by the sphenoidal beak or rostrum. The upper surface of the body is endocranial. From front to back there are the following structures:

The quadrilateral lamina, the sella turcica (which houses the pituitary gland) and then the optic canal that ends at its ends with the optic canals. In turn, the sella turcica is limited by the clinoid processes, two anterior and two posterior.
On the underside, the body has in the center the middle crest that is housed in the vomer canal. It is prolonged by a spur called the rostrum or beak of the sphenoid.
The anterior aspect of the sphenoid articulates with the posterior aspect of the ethmoid. In its center it shows the anterior crest that joins with the crest of the underside to form the beak. On both sides are the entrance holes to the sphenoid sinuses.
The posterior face articulates with the occipital.
The lateral faces serve as the implantation point for the greater wings. These are separated from the sella turcica by the cavernous canals through which the internal carotid artery and some nerves destined for the orbit run.

Lesser wings

Also called Ingrassia processes, they have a triangular shape with two more or less flat faces. The base, welded to the body of the sphenoid, is crossed by the optic canal.

Greater wings

They have the shape of 3-pointed stars, with three faces distinguished. The anterior surface is part of the external wall of the orbit. In the greater wings there are a series of holes and slits for the passage of nerves and vessels. The most important are: Foramen rotundum , through which the upper maxillary nerve passes, the spheno-spinous foramen through which the middle meningeal artery passes, and the foramen ovale, which gives way to the lower maxillary nerve. The Foramen of Arnold or innominate canal of Arnold gives way to the lesser superficial petrosal nerve, while the Foramen of Vesalius gives way to an emissary vein that puts the intracranial circulation in communication with the pterygoid venous plexus.

Pterygoid process

They appear as two bony columns located at the bottom of the bone. It has a quadrangular shape. Recent studies suggest the hypothesis according to which changes (due to mutation) in the position of the sphenoid have implied transformations in brain capacity and, transitively, advances in cognitive and intellectual abilities.

Within the phylogenetic line that leads to Homo sapiens, the following stages are periodized:

60 million years ago, prosimians had a flat, horizontal sphenoid like the vast majority of other animals with brains.
About 40 million years ago, in apes the sphenoid had an initial downward inclination which allowed an increase in brain capacity. The occipital lobes obtained more space and thus an improvement in stereoscopic vision and probably visual memory was achieved.
Less than 12 million years ago there was a new downward inclination, this in the evolutionary line gave rise to anthropoids, which implies an even larger brain in proportion to the rest of the body.
About 6 million years ago, with the Australopithecus, the inclination of the sphenoid was accentuated again, and with this the neurocranial capacity increased.
2 million years ago the same downward inclination of the sphenoid occurred, coinciding with total bipedalism. Such bipedalism implies the need for a voluminous brain with complex neural networks to maintain that position opposite to gravity. It is also likely that this new position of the sphenoid allowed rudimentary speech, whose phonemes were clicks and guttural tones.
Between 200,000 and 160,000 years ago the sphenoid obtained the inclination found in Homo sapiens. This fact coincides with an increase in brain capacity (especially the frontal lobes) and greater blood supply to the brain.