foramen magnum

Bone: Foramen magnum
Occipital bone. Inner surface.
Gray's	subject #31 129
MeSH	Foramen+Magnum

In anatomy, in the occipital bone, the foramen magnum (Latin: 'great hole') is one of the several oval or circular apertures in the base of the skull (the foramina), through which the medulla oblongata (an extension of the spinal cord) enters and exits the skull vault.

Apart from the transmission of the medulla oblongata and its membranes, the foramen magnum transmits the Spinal Accessory nerve, vertebral arteries, the anterior and posterior spinal arteries, the membrana tectoria and alar ligaments.

Importance

In humans, the foramen magnum is farther underneath the head than in other great apes. Thus, in humans, the neck muscles do not need to be as robust in order to hold the head upright. Comparisons of the position of the foramen magnum in early hominid species are useful to determine how comfortable a particular species was when walking on two limbs (bipedality) rather than four.

The foramen magnum is the border line above which is the brain, and below, the spinal cord.

Additional images

Occipital bone. Outer surface.

Base of skull. Inferior surface.

Base of the skull. Upper surface.

Human brain dura mater (reflections)

See also

• Posterior cranial fossa

External links

• SUNY Figs 22:4b-10
• cranialnerves at The Anatomy Lesson by Wesley Norman (Georgetown University) (XI)
• Roche Lexicon - illustrated navigator, at Elsevier 34257.000-1

This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained herein may be outdated.

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