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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
Zipf's Law 
No problem with masticatoire, adjectives ending with an “e” are identical at the masculine and feminine forms .
From the same root in French there is “le mors”, that is called in English the bit, the piece put in horses mouth . And the expression “prendre le mors aux dents”, to fly off the handle .
Mordant is an adjective used figuratively : un froid mordant, as in English a biting cold, and also “une critique mordante”, “un commentaire mordant”, again as in English .
You could have mentioned la mandibule, the mandible .
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Thanks for the additional words, and the feedback on the adjective.
I’m working on a post on the mandible. 🙂 Lots of picture-formatting problems with WordPost lately, and that’s slowing me down quite a bit.
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I confirm that French bulldogs don’t have one. Thanks for the interesting anatomy lesson!
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I was puzzled by all this, maybe because I’m not a pet person…. ?
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Rub your head along the center of a few dogs’ heads when you get a chance. Some of them will have a sagittal crest. Or, stop by my office–I keep a racoon skull around. 🙂
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Joking or did you hunt it or something?
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“Or something.” 🙂 I have two skulls in my office:
1) I brought a pig head home from a picnic once. Trying to deflesh it, I boiled it frantically, ’cause I knew that if my wife came home and found pork in our pork-free home, she was gonna be PISSED. Meanwhile, my dogs danced about frantically–I’m not sure I’ve ever seen them so excited. I managed to avoid horrible accidents with canines and boiling water. Then I left it under my barbecue grill for a year and let the bugs take care of the rest.
2) I bought a racoon skull in an amazing store in San Francisco. I try not to own anything, and I mostly don’t, but this just was not resistable.
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You have a fascinating existence …
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I have a crest beginning just above the curve of the top of my forehead and ending at the curv down the back of my head. Could this be the results of forceps birth or do any modern humans have a true sagittal crest?
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Remarkable how you learnt how to stand up on two feet !
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I tend to avoid words like “always,” “never,” and their relatives, since in science (and life), they’re not true very often. I’ll say just that I’ve looked at a lot of modern human skulls, and I’ve never seen a sagittal crest on one, nor have I ever read a description of a modern human skull with a sagittal crest. If you run across such a thing: I would love to hear about it!
Regarding forceps deliveries: I spent a little while looking at recent publications on forceps deliveries, and didn’t find anything suggesting that a forceps delivery could lead to the development of something like a sagittal crest. On the other hand, I didn’t spend very long searching for it, either, primarily because I can’t think of any mechanism that could lead to it–confirmation bias, perhaps. I’ll also point out that the studies that I have found talked only about immediate perinatal effects, so something like a later skull deformity wouldn’t be reported in those papers anyway. As I said, though: truly, I can’t think of a way that anything that you could do with forceps to a neonate’s skull could lead to a sagittal crest later. Bear in mind that in the neonate, the parietal bones (the ones that join at the sagittal suture in the adult) are not yet touching.
If you come across data that suggests otherwise: I would love to hear about it!
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I got. so does my brother and father. I have read that it is not a true sagittal crest when it appairs on sapiens, but i can’t help to think if it excisted amongst homo erectus it can on some.
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