What is the Calvaria?

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  • Written By: Daniel Liden
  • Edited By: Jenn Walker
  • Last Modified Date: 15 June 2017
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The calvaria, also known as the skullcap or the calvarium, is the upper or superior part of the skull. It does not contain the bones that make up the jaw or the parts of the skull that make up the face. The calvaria is made up of four primary bone structures: the frontal bone, the two parietal bones, the two temporal bones, and the occipital bone. It is a thick and hard structure that primarily exists to protect the brain from harm. Its shape varies from person to person; in some people, the skullcap takes the shape of an oval, while in others it is almost perfectly circular.

The frontal bone part of the skullcap makes up the forehead and the tops of the eye sockets and nasal cavities. The two parietal bones together make up the sides and the top of the cranium, or upper part of the skull, excluding the lower jaw. The two temporal bones are lower on the sides of the skull; they support the temples on the sides of the face. The occipital bone is situated at the lower back section of the skull. Together, these bone structures make up the calvaria.

In infants, the skullcap is formed through a process referred to as intramembranous ossification in which bone develops from a tissue or membrane structure. The word ossification specifically refers to any process that involves a substance or structure changing into bone. The term intramembranous refers to the fact that the substance being turned into bone is some form of connective tissue as opposed to cartilage. Many bones, including much of the lower part of the skull, are formed through endochondral ossification, which is the formation of bone from cartilage. All of the different parts of the calvaria, however, start as soft and vulnerable membranous tissue that hardens into solid bone.

One feature of the calvaria that is present on the skulls of infants is the presence of fontanels, or soft spots. These allow the skull to flex and bend to some degree, allowing the infant to fit through the birth canal. Many parents are often concerned that their infant is at significant risk of harm because of the existence of the soft fontanels. This is not the case as the membranes that make up the fontanels are very durable and strongly resistant to damage. There are some conditions in which the fontanels are exceptionally large; sometimes, these never completely transition to hard bone.

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bythewell
Post 3

@Mor - Actually this practice was relatively common once upon a time. The Mayans and the Aztecs both did it, to flatten the forehead.

And they think that the Ancient Egyptians did it as well, although to a lesser degree. If you've ever thought that paintings of some of the pharaohs looked like they had strangely shaped skulls, well, in fact they did.

Actually if you look up pictures of the skulls, it's amazing how different they look. It actually makes you wonder if extraterrestrial, or fairy stories came from people digging up the skulls of ancestors who practiced this, because they look very alien.

They think it might have been done to show status, but they aren't really sure. I don't think, thank goodness, that any groups currently practice it.

Mor
Post 2

@pleonasm - While it's true that those spots are stronger than people think they are, they are still weaker than bone, so it does pay to be careful.

One of the things I find interesting (and kind of grotesque) about it is that there have been cultures in the world who used to shape the baby's calvaria while it was still malleable like that. They would fit a mold around the head so it would grow narrower, for example, so the adult would end up with a long skull.

I'm not sure if it actually damaged the brain or not. I suppose if the brain was just forming it might not do much damage, as the brain would just adapt.

But still it seems really scary by our cultural standards.

pleonasm
Post 1

I was one of those people who was always terrified of the fontanels. My parents told me, when my sister was a baby, that I should never, ever touch the top of her head, because there was a soft spot there and if I touched it the wrong way, I could kill her.

Of course, now that I think about it, if that were really true of baby skulls, we all would probably have died off as a species by now. I know when my sister was a toddler she was always bumping into things and the "spot spots" aren't supposed to completely close up until baby is a couple of years old.

But, when they first told me that I was utterly convinced that if I wasn't extremely vigilant about not touching her skull, I would accidentally kill her.

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