Sphenoids . 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. Altogether, the sphenoid consists of a cubic body, two smaller wings attached to the upper body, two larger wings attached to the lateral sides of the body, two pterygoid processes as a landing gear, and two hooks, for behind these.
Summary
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- 1 Body
- 2 minor wings
- 3 Greater Wings
- 4 Pterygoid process
- 5 Sources
Body
It has a cubic shape and shows two cavities (like the front windows of the spacecraft), the sphenoid sinuses, separated by a middle septum (sphenoid intersinusal septum). This septum tapers forward to form the sphenoid crest (much like the bow of the spacecraft) that is prolonged by the sphenoid beak or rostrum. The upper face of the body is endocranial. From front to back are the following structures:
- The quadrilateral plate, the sella turcica (which houses the pituitary gland) and then the optical channel that ends at its ends with the optical channels. In turn, the Turkish chair is limited by the clinoid processes, two anterior and two posterior.
- On the underside, the body presents in the center the middle crest that is housed in the vomer channel. Prolonged is a spur called the rostrum or sphenoid peak.
- The anterior aspect of the sphenoid articulates with the posterior part of the ethmoid. At its center it shows the anterior ridge that joins with the ridge on 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 an implantation point for the greater wings. These are separated from the sella turcica by the cavernous channels through which the internal carotid artery and some nerves destined for the orbit run.
Minor wings
Also called apophysis of Ingrassias, 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 optical conduit.
Greater wings
They have the shape of 3-pointed stars, with three faces being distinguished. The anterior face 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 the nerves and vessels. The most important are: Round hole , through which the upper maxillary nerve passes, the spinous sphene hole through which the middle meningeal artery passes, the oval hole that leads to the lower maxillary nerve. The Arnold’s Hole or Arnold’s unnamed canal gives way to the minor superficial petrous nerve, while the Vesalian’s Hole gives way to an emissary vein that connects the intracranial circulation 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 that changes (by mutation) in the position of the sphenoid have implied transformations in brain capacity and, transitively, advances in cognitive and intellectual capacities.
Within the phylogenetic line leading to Homo sapiens, the following stages are periodized:
- 60 million years ago prosimians had a flat, horizontal sphenoid like the vast majority of other brain animals.
- About 40 million years ago, in the apes the sphenoid had a first downward inclination which allowed an increase in brain capacity. The occipital lobes gained more space and thus improved stereoscopic vision and probably visual memory.
- Less than 12 million years ago there was a new downward tilt, 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 Australopithecus, the inclination of the sphenoid was accentuated again, and with it the neurocranial capacity was increased.
- 2 million years ago the same downward tilt 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 probable that this new position of the sphenoid allowed rudimentary speech, the phonemes of which 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 in the frontal lobes) and an increased blood supply to the brain
