Our example tells me that the shoulder joint is the most mobile joint in the body, and it wants me to describe how the structures of the pectoral girdle aid in making the shoulder so mobile. And what it wants me to talk about, the glenoid cavity, the scapula, and the clavicle. Now as a visual aid, it shows me the pectoral girdle right here. It also shows me the humerus and the thoracic cage as a reference.

Alright. So first off, let's talk about the glenoid cavity. Do you remember how the glenoid cavity contributes to shoulder mobility? Well, we said the glenoid cavity, that's the socket in the ball and socket joint. And when we look at the scapula, we see it's really shallow. I said it's more like a golf tee than like a real socket. And when you take the humerus there, that means that it has a ton of mobility. It doesn't sit way in that that socket itself doesn't bind the humerus. So the glenoid cavity, we're going to start off just by saying that it is a shallow socket, and it being shallow allows that humerus to move around a lot.

Next, though, we want to just talk about the scapula in general. What about the scapula in general aids that shoulder mobility? Well, we said the scapula moves around a lot. Right? It's only articulated to the axial skeleton directly through the clavicle, and the attachment point's way out here at the acromion process. So when you move your arms, your scapula moves. Right? You can pinch it back. You can bring it forward. And when you're doing that, you're changing the angle of the glenoid cavity, which adds more mobility to that shoulder joint. So I'm going to say the scapula itself, I'm just going to sort of say that it is a mobile bone. It moves around a lot, and as it moves, it changes the orientation of that shoulder so you can move your arm even more.

Finally, it wants us to talk about the clavicle. So what about the clavicle aids in this mobility? Well, remember the clavicle, as you move your shoulder around, if you have your arm on it, you can feel the clavicle moving. So the clavicle itself, we said it has 2 mobile joints. And it again is going to allow that shoulder to change its orientation, to change the way that the glenoid cavity faces, to allow you to move your arm a lot.

Now this is all going to be in contrast to the pelvic girdle, which we haven't talked about yet. But the pelvic girdle where your legs attach, it's got a really deep socket and those bones aren't mobile. They don't move around. That's why you can swing your arm all around and you can't do it nearly as much with your leg. So next time you're raising your arm up above your head in class, remember you can put it up that high because of the glenoid cavity, the scapula, and the clavicle.