 So the great vessels are blood vessels that enter and exit the heart itself. Now, if you look at our diagram here, I've only drawn the great vessels. I've only drawn vessels that directly enter or exit the heart. If you look at this drawing, you'll notice that we actually have some branches, and of course we have branches. The whole thing is going to branch, and we're going to have mad branches everywhere. And the branches are what we're going to talk about in the next piece. In the next lecture, we're going to figure out, like, what is the name of this branch? And where does it go? And what does it turn into when? And we'll follow it all the way through and be able to fill in some of the details. But the great vessels, all we're going to worry about today are just the vessels that directly come in and leave the heart. So if we have our super simple body boxes and lung boxes, that's all we need. We just need to know that this is going to take us to the lungs. You know that we're going to have all sorts of branching and naming of those branches on our way to the lungs and back from the lungs. But all we care about are the ones that come in and out of the heart themselves. So we're going to start thinking through the great vessels that are involved in the systemic circulation, as opposed to the great vessels that are involved in pulmonary circulation. And what I want you to think about is, if we're associated with body, that's systemic. That's part of the systemic circulation, circulatory system, systemic. And if it's associated with the lungs, if the vessel, the great vessel is going to or from the lungs, that's part of the pulmonary system. And really, I mean, your heart really does have two pieces. Part of the circulatory system that we're going to talk about today is the actual names of the vessels that feed the heart itself, and that's the coronary circulation. And then next time we'll deal with all the details in both of these branches. Okay, so let's talk about the systemic system first.