As we learn the bones of the skull, some structures that you're very likely going to need to know about are the sinuses. Now, sinuses are just air-filled cavities that are lined with mucosa, and mucosa is just a tissue that produces mucus. So, these air-filled cavities are going to be really moist inside. They are going to be found inside of bones, but they're also going to be connected to the nasal cavity. So sometimes, these are called the paranasal sinuses. Now, these are doing a few things for you. First off, they are going to lighten the skull. And by that, I just mean bone is a heavy tissue and air is lighter than bone. So if you have a cavity in the bone that's not filled with bone tissue, but instead it's filled with air, your head is just going to be lighter. And so, to signify that, we have a little image here of some hot air balloons, showing how that makes your skull lighter. Next, we are going to say that they work to warm and humidify the air, and to show that, we have a little stove here with a fire showing it's warming, and then a little humidifier next to it. Now, when you breathe in, you're breathing air down into your lungs, which is really sensitive tissue. So the more surface area that you can get along the way that is warm and moist, well, the more evaporation into that air is going to happen, and just the warmer and more conditioned that air will be when it makes it down into your lungs. And the sinuses are doing some of that for you, as well as the rest of your nasal cavity. Finally, it is going to enhance vocal resonance. And by this, I mean, if you've ever seen like an acoustic guitar, it has this box on the back with a hole in it. That gives an acoustic guitar that nice, loud, rich sound. That box is a resonator box. If you compare that to an electric guitar that's not plugged in when you play it, it really doesn't sound very good. Now that's pretty similar to your voice. And to illustrate this, we have a guy singing here. But, if you've ever tried to talk with a really bad cold where your nasal cavity is all blocked up, you can't use those resonance chambers of the sinuses. And so when you talk like this and you say you have a really nasally voice, it's because you're not getting the resonance of the nasal cavity and of the sinuses. Okay. So let's name our paranasal sinuses here. They're going to be found in these four bones. First off, we have some in the frontal bone, and those are aptly named the frontal sinuses. And we can see here we have a picture of a woman showing the different sinuses that are color-coded. And here we have the frontal sinuses in the frontal bone, that bone of the forehead sort of in your brow ridge right up here. Next, we have the ethmoid bone has the ethmoid air cells, and that's these little marks here in green. Remember, the ethmoid bone, technically a cranial bone, but it makes up a lot of that internal architecture of the nasal cavity. Now, these are called the air cells because you see over here; there are a few of them. They're not just one cavity. The ethmoid air cells are a bunch of smaller little sinuses within this bone. After that, we have the maxillary sinus in the maxilla, and you see over here in purple, filling up a lot of the front of the cheek here, all in here, the maxilla, those bones are hollow. They have these big sinuses in them. Lastly, we have the sphenoid bone has the sphenoid sinus, and you see in yellow here well, remember the sphenoid bone is a cranial bone. It's that bat-shaped bone at the front of the cranium, so all the way in the back of the facial bone. So this is going to be at the back of the nasal cavity. Now to remember these, we have just a real quick little word here. You can say fems. Where are my sinuses? Fems. They are in the frontal bone, the ethmoid bone, the maxilla, and the sphenoid bone. Alright. With that, those are the sinuses. We'll see you in the next video.