 Our lungs are protected by our ribcage. Beneath the ribs and above the diaphragm, we call this space the thorax. The lungs occupy the majority of this space. The right lung has three lobes. The left only has two because it has to share its space in the thorax with the heart, which sits in this pocket here. To mark out the fissures between the lobes, we're going to bring down the complexity of the models so that their borders are nice and distinct. And now that we've done that, let's draw the borders between the lobes which we call the fissures of the lungs. We'll start with the right lung. Both lungs have oblique fissures, so let's draw that one out first. Around the front, it separates the lower lobe from the middle lobe. Let's draw that one in. Going around the side, the middle lobe finishes, so the oblique fissure now separates the lower lobe from the upper lobe. The horizontal fissure separates the middle lobe from the upper lobe. So let's draw that one in too. Barely straight or horizontal around the front, and then it meets up with the oblique fissure around the side. Okay, now let's smooth our models out and see if these lines match what you might have learnt in anatomy class. So we can still see our fissure lines underneath our rib cage. And we're told that the oblique fissure in black corresponds to the sixth costal cartilage at the front. So let's find that. One, two, three, four, five, six. That's great. It crosses the fifth intercostal space laterally, so that's the space between rib six and rib five. And then it finishes around the spinous process of the fourth thoracic vertebra. So that's T1, T2, 3, 4, and there's its spinous process. And that's pretty damn close. Now for the horizontal fissure. That's supposed to start at the fourth costal cartilage. One, two, three, four. Yep, and then it traces around to hit the oblique fissure. Great. I should mention that around this side, they all end up back at the hilum of the lung, which is roughly this area here, where all the vessels and the bronchi plug in. Okay, let's move on to the left lung now. We'll get rid of the right lung and its associated lines. The oblique fissure on the left lung starts down here, moves steeply toward the posterior lung and continues to move superiorly on that surface. Let's smooth out our models and admire our handiwork for a second. Now in context, let's find out if our line was accurate. The left oblique fissure corresponds pretty well with the same on the right. So this should be our sixth costal cartilage. Yep, then the fifth intercostal space again. Then just a bit higher than where we ended up on the right hand side, bringing everything back in. Yep, we can see that pretty well there. If you found this video useful, hit the subscribe button below. I've put a link to this model in the video description. So have a look around yourself if you'd like further clarification. Thank you very much for watching and we will see you next time.