We're going to finish up the axial skeleton by talking about the thoracic cage. The thoracic cage, or what you probably just know as the rib cage, is there to protect the thoracic cavity. Remember, the thoracic cavity is that cavity inside your chest that houses, importantly, your lungs and your heart. Now it's also going to provide structure for your body, and really importantly, structure for the lungs. Your lungs do not work without ribs. We'll talk more about that in the respiratory unit.
So, the thoracic cage consists of the thoracic vertebrae—those 12 vertebrae that articulate with ribs, the ribs, the sternum, and the intercostal cartilage. We have those things color-coded over here in our image. You can see the thoracic cage and the vertebrae. We also have the collarbones and the shoulder blades drawn on here for reference.
Now, let's talk about the ribs. The ribs are 12 pairs of flat bones that wrap around the chest. Quick little misconception check: I've heard some people say before that females have one less rib or one less pair of ribs. That comes from the Adam and Eve story. However, there's no difference between sexes in terms of numbered ribs. Some people have an extra pair of ribs, but that's just a rare bit of human variation. You have 12 pairs of ribs, and we can number them just like we did the vertebrae, counting down from the top: 1, 2, 3, 4, 5, and so on down to 12. The first seven ribs—ribs 1 through 7—we're going to call the true ribs because they attach to the sternum directly via their own piece of costal cartilage. You can see on the image, those first seven ribs, which are a little bit darker pink, have a piece of costal cartilage going straight over to the sternum without connecting to any other piece of cartilage.
This is going to be different for the 5 bottom ribs. We call the five bottom ribs the false ribs, and they attach to the sternum either indirectly or not at all. The first three false ribs have costal cartilage attachments, but the costal cartilage connects to other costal cartilage before it connects to the sternum. The last two false ribs we call floating ribs because they have no sternal attachment. Like all ribs, they articulate with the vertebrae posteriorly, but these last two ribs, shown in dark pink and labeled 1c, have no connection anteriorly to the sternum. Knowing the difference between true, false, and floating ribs is a question that you'll often see, so I'd really familiarize yourself with it.
Next up, we have the sternum, which we've been talking about a little bit. Your sternum, also called your breastplate sometimes, is a flat bone that can be seen in purple here in the drawing. It kind of looks like a necktie. This bone, this flat necktie, is actually made up of three bones that fuse together, and you're probably going to need to know those individual bones. The knot of the necktie up here at the top, that's the manubrium. The long part of the necktie, that’s the body, and then this little tip sticking down off the bottom there, that’s the xiphoid process, which can be felt sticking down a bit. It kind of hurts to press on and serves as an attachment point. To help remember those, here's a little memory tool: you can say, "Mark the body with an X," referring to the manubrium, the body, and the xiphoid process.
Lastly, we're going to talk about the intercostal cartilage, which we've already discussed somewhat. This connects ribs 1 through 10 to the sternum, comprising the seven true ribs plus the first three false ribs. It provides a flexible and strong connection. You do have a little bit of flexibility in your rib cage, and a lot of that comes from the flexibility of the costal cartilage and those joints, but it also has to be really strong because it’s protecting what’s inside your thoracic cavity and providing structure to your body.
With that, that's the thoracic cage. Like always, examples and practice problems to follow. I'll see you there.
