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In America, we do love our dogs. A culturally common way for us to show our dogs affection is this: we pet them, while saying Who’s a good boy? (or Who’s a good girl?, depending on gender). In my family, we do it a little differently: we pet the dog while saying Who’s got a sagittal crest? Dogs don’t look at you with any more or less puzzlement regardless of which one you pick, so: feel free to go crazy with this one.
What’s a sagittal crest? The next time you run into a dog, run your hand along the center of the top of his skull. That ridge that you feel is his sagittal crest. Sagittal means along a plane that runs from the front to the back of the body. A sagittal crest runs along that plane. This sense of crest means something sticking out of the top of the head–think the plume on top of a knight’s helmet. Many animals have a sagittal crest, but not us modern humans. You see them in species that have really strong jaw muscles. A sagittal crest serves as one of the points of the attachment of the temporalis muscle, which is one of the main muscles used for chewing. If you have a sagittal crest, you can have a bigger temporalis muscle, which means that you can bite/chew harder.
If you look at relatively close relatives to humans, you see sagittal crests on some of them. To the left, you see a gorilla. You wouldn’t want to get bitten by this guy. (Note that some gorilla species, especially their males, have really enormous sagittal crests–this is actually a pretty modest one, for a gorilla.)
Here’s (an excellent replica of) a Pan troglodytes (common chimpanzee) skull. This guy (I think it was a guy) had more of a sagittal crest than you (you don’t have any), but he didn’t have much, compared to that gorilla. Other chimps vary. Monkey species vary pretty widely regarding the presence or absence of a sagittal crest.
Some hominids that were ancestral to us had sagittal crests, but they disappeared pretty early in the course of our evolution. Here is a picture of the “Black Skull,” about 2.5 million years old. It’s from a type of Australopithecus robustus. By the time Homo erectus comes along (starting about 1.9 million years ago and lasting until about 70,000 years ago), the sagittal crest is gone. Picture below.
So: feel free to express your affection for your dog any way you want–you can’t possibly be any geeker than my son and me. Scroll down past the picture for French vocabulary.
Relevant French vocabulary (see the Comments section for more):
- la crête sagittale: sagittal crest
- le muscle masticatoire: chewing muscle (note: the “c” in muscle is pronounced in French)
- le muscle temporal: temporalis muscle
- la morsure (action de mordre): bite (noun)
- la morsure (marque de dents): teeth marks