Foramen magnum

Bone: Foramen magnum
Upper surface of base of the skull. The hole indicated by an arrow is foramen magnum
Occipital bone. Inner surface.
Latin	Foramen magnum
Gray's	subject #31 129
MeSH	Foramen+Magnum

In anatomy, the foramen magnum (Latin: "great hole") is a large opening in the occipital bone of the cranium. It 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 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 great apes. Thus, in humans, the neck muscles (including the occipitofrontalis muscle) 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 (bipedalism) rather than four (quadrupedalism).

Additional images

Skull seen from below. The hole through which medulla(shown in red) is passing is foramen magnum.  Skull seen from above (parietal bones removed). Foramen magnum is shown in red.  Occipital bone. Foramen magnum shown in red.  Foramen magnum  Occipital bone. Outer surface.  Base of skull. Inferior surface.  Base of the skull. Upper surface.  Human brain dura mater (reflections)  Tympanic cavity. Facial canal. Internal carotid artery.

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 incorporates text from a public domain edition of Gray's Anatomy.