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What is the Foramen Magnum?

Katriena Knights
Katriena Knights

Anatomically, a foramen is a hole or passage, usually through a bone. The foramen magnum, or "great hole," is the hole in the bottom of the skull through which the spinal cord passes in order to connect to the brain by merging with the brain's lowermost portion, the medulla oblongata. Passing through the occipital bone, it is the largest opening in the base of the skull, though there are several others. Several other nerves, blood vessels and tendons also pass through the hole.

When evaluating skeletons, the angle of the foramen magnum tells scientists whether the head of the animal in question was carried in a horizontal position, as in most four-legged creatures, or in a more vertical position, as in bipedal animals. Anthropologists also have used this measurement of the position of the hole to determine the ability of human ancestors to walk upright. In modern humans, the passage is located more toward the back of the head than in the great apes, so that less heavy musculature in the neck is required to support the skull.

The foramen magnum is the hole in the bottom of the skull through which the spinal cord passes in order to connect to the brain.
The foramen magnum is the hole in the bottom of the skull through which the spinal cord passes in order to connect to the brain.

Occasionally, congenital issues lead to a condition called foramen magnum stenosis, in which the opening is not large enough for the spinal cord to easily pass through. This most often happens in conjunction with achondroplasia, a condition in which bones and cartilage do not form properly, causing a form of dwarfism. In all children who have this condition, the opening is smaller than normal. This often does not present a danger to the patient's overall health, but in about 5% of children with achondroplasia who suffer from an abnormally small passage, the reduced size causes compression to the spinal column, which can be dangerous and even fatal.

Achondroplasia is a disorder associated with cartilage that typically results in dwarfism.
Achondroplasia is a disorder associated with cartilage that typically results in dwarfism.

In cases of achondroplasia that include spinal cord compression, surgery is necessary to prevent long-term disability or death. Considerations of this surgery can be complex because of the special needs of children born with the condition that leads to the malformation of the foramen. The best results usually can be expected from surgeons who have had experience not only with the stenosis, but also with achondroplasia.

Surgery can prevent long-term disability or death in children with achondroplasia who also develop foramen magnum.
Surgery can prevent long-term disability or death in children with achondroplasia who also develop foramen magnum.

Children with achondroplasia have a much higher mortality rate than the general population. A large percentage of these deaths are believed to be related to spinal cord compression. Because of the danger of sudden death, it is important that these children be treated as soon as possible to correct the problem.

Discussion Comments

sherlock87

I think it's fascinating that this one skull cavity can tell us so much about the way than a species may have walked and moved. I have heard before about things like teeth showing what animals ate, and arm and leg sizes showing how they walked or stood, but this is even more surprising to me.

Denha

I mentally always associate the word "magnum" with a gun. It is very strange how much popular culture affects our word usage and mental association. I know even less about guns than I do about human anatomy and brain function.

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    • The foramen magnum is the hole in the bottom of the skull through which the spinal cord passes in order to connect to the brain.
      By: Gufh
      The foramen magnum is the hole in the bottom of the skull through which the spinal cord passes in order to connect to the brain.
    • Achondroplasia is a disorder associated with cartilage that typically results in dwarfism.
      By: Nolte Lourens
      Achondroplasia is a disorder associated with cartilage that typically results in dwarfism.
    • Surgery can prevent long-term disability or death in children with achondroplasia who also develop foramen magnum.
      By: Patrick Hermans
      Surgery can prevent long-term disability or death in children with achondroplasia who also develop foramen magnum.
    • Surgery will be required to treat cases of achondroplasia that include spinal cord compression.
      By: Photographee.eu
      Surgery will be required to treat cases of achondroplasia that include spinal cord compression.