Foramen magnum

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The foramen magnum (Latin: big hole ) is a large oval opening ( foramen ) in the skeletal occipital bone in humans and various other animals. This is one of several oval or circular openings ( foramina ) at the base of the skull. The spinal cord, an extension of the medulla , passes through the foramen magnum as it exits the skull cavity.

Regardless of the transmission of the medulla oblongata and its membrane, the foramen magnum transmits the vertebral artery, the anterior and posterior spinal arteries, the tectorial membrane and the ligaments of the alar. It also transmits components of the accessory nerve spine to the skull.

The opisthion is the midpoint of the posterior margin of foramen magnum and is a cephalometric landmark. The other marker is basion located at the midpoint of the anterior margin of foramen magnum .

The foramen magnum is a very important feature in bipedal mammals. One of the attributes of the bipedal animal foramen magnum is the forward shift of the anterior border; this is due to the cranial base shortening. Studies on the foramen magnum position show a relationship with the functional effects of posture and body movement. The forward shift of the foramen magnum is evident in bipedal hominins, including modern humans, Australopithecus africanus , and Paranthropus boisei . A common feature of bipedal hominins is the driving argument used by Michel Brunet that Sahelanthropus tchadensis is also bipedal, and perhaps the earliest known bipedal ape. The discovery of this feature has given scientists another form of identification of bipedal mammals.

Video Foramen magnum

Compartment

The ligament of the altar attached to each side to the tuberkul of the occipital condyle on each side of the foramen magnum divides it into smaller compartments and larger compartments;

Structures that pass through the osseo-ligament (anterior) compartment are:

• Apical ligament and nest end
• Ribbon over Cruciatum ligament
• Membrana tectoria

Structures that pass through the neuro-vascular compartment (posterior) are:

• Bottom end medulla oblongata with meninges
• The fourth part of the vertebral artery surrounded by a sympathetic nerve plexus
• The spinal root of the accessory nerve
• Anterior and posterior spinal arteries
• Tonsils from cerebellum (sometimes)

Maps Foramen magnum

Other animals

In humans, the foramen magnum is further below the head than in the other great apes. Thus, in humans, the neck muscles (including occipitofrontalis muscle) do not have to be strong to hold the head upright. The comparison of foramen magnum positions in early hominid species is useful for determining how comfortable a particular species is while walking on two limbs (bipedalism) rather than four (quadrupedalism).

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Additional images

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See also

• Posterior cranial fossa

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References

This article combines text in the public domain of page 129 of the 20th edition of Gray's Anatomy (1918)

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External links

• "Anatomical diagram: 34257.000-1". Roche Lexicon - illustrated navigator . Elsevier. Archived from the original in 2014-01-01.
• Diagram 1
• Diagram 2
• 3D animation that shows the position of basion on YouTube

Source of the article : Wikipedia