7. The Skeletal System
The Thoracic Cage
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Our example tells us that the image below shows 2 ribs. 1 is rib 10 while the other is rib 11. How can you tell which is which? Alright. On its surface, this sounds like a really hard question, and you should not need to be able to just pick up a random rib and say what number rib it is, 1 through 12. But think for a second, what is different between rib 10 and rib 11? Well, when we count the ribs, we count the pairs of ribs from the top. So rib pair number 1 is at the top, ribs 12, they're at the bottom. As we count down, remember those first 7 ribs, those were your true ribs. And those pairs of ribs connect to the sternum directly with their own little piece of costal cartilage that connects them to the sternum. The last five pairs of ribs we call the false ribs, and that's because they do not connect to the sternum directly or they don't connect at all. Either they have costal cartilage that comes up and connects to other costal cartilage before running into the sternum, or they don't have any costal cartilage attachment to the sternum at all. It's those last two ribs, which we call the floating ribs, that have no costal cartilage attachment. So with that in mind, what do you think is different between 1011? And take a look at the picture What cues you in to which is which? Well, as I look at the picture, I see here this rib in the front, it has this sort of blunt section and it looks like it has some cartilage there, where this one just comes to a point. Well, rib 10 is going to be a false rib, but it's gonna have costal cartilage that runs up and connects to other cartilage and eventually runs into the sternum. So when I see this blunt end in that cartilage there, that tells me this one must be rib 10. And my reasoning, I'm gonna say it has cartilage attachment. Now in contrast, I look at over here, this rib ends in a point. It's not attaching to any cartilage. So that must be one of my floating ribs. A floating rib is gonna be rib 11 or 12, but here it tells us it's rib 11. So my reasoning, no cartilage attachment. Again, you shouldn't have to be able to just pick up a single rib and say what number it is, 1 through 12, but you should be familiar enough with ribs that you can describe the difference between those true ribs, the false ribs, and then among the false ribs, what's different about the floating ribs? There we go.
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