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• In the last episode we learned the anatomy of the rib cage. If you haven’t seen that

• one yet, make sure you don’t miss it.

• In this episode, I’ll show you how to draw the forms of the rib cage step by step.

• I always like to start my drawings with the biggest shapes first. In this case it will

• be the egg-like shape. It’s thinner at the top where the neck attaches, and thickest

• aboutfrom the bottom. Try not to draw the entire shape with one stroke. Construct

• the shape with many segments, analyzing the angle of each line as you go. Constructing

• a shape from many angles like this allows you to visualize the shape and spend more

• time making sure it’s the correct shape. Rather than doing it in one stroke hoping

• your hand lands in the right spot.

• You can see how with this shape I established the angle of the top plane, front plane, the

• angle between the corners of the rib cage, and the curve of the bottom and back. I’m

• being specific about each section of the shape while maintaining the tilt and the width to

• height relationship of the overall shape.

• The top plane of the rib cage tilts forward, so keep that in mind as you try to visualize

• the planes.

• Find the bottom of the sternum. Remember, it’s about half way between the pit of the

• neck and the bottom of the rib cage.

• The cartilage that defines the thoracic arch starts from the bottom of the sternum. So,

• from there I’ll extend the thoracic arch shape, while considering the way perspective

• would affect that shape.

• I like to relate one side to the other and make sure that the angle of that line follows

• the angle of the front plane as if this was a box. I’ll do a simplified version of the

• rib cage after this to show you what I mean.

• This side of the bottom plane is covered up, but I’ll ghost it in anyway so I can visualize

• these forms better.

• Indicate the edges of the sternum, curving over the front plane.

• A little notch in here for the xiphoid process

• And we need an indication for the edge between the front plane and side plane. This is like

• the edge on the box.

• Everything on the front or back plane will be at this angle, like a box in perspective.

• Let me show you what I mean when I talk about the rib cage being a box.

• Well think of the front of the rib cage as this flat plane that’s rotated slightly

• to the left and downward.

• The widest part of the rib cage isfrom the bottom, so from there I’ll extend a

• plane inward. Still part of the front plane just getting narrower.

• From that, we can complete the box with a side plane and top plane.

• So, we have the big simplified volume of the rib cage, and we can just draw the shape of

• the thoracic arch right on it. Start by finding the bottom of the sternum and then some major

• angles downward toward the corners.

• And since the thoracic arch is an opening, we can see the bottom edge on the far side.

• It will be parallel to the other bottom edge.

• Let’s clean up this back side.

• Ok, so that’s the front of the rib cage. The major structure from the back is very

• similar, but the wedge shape at the spine is a bit tricky, so I want to show you how

• to do that.

• Start the major shape in the same way I do for the front. Constructing that shape in

• parts.

• For this bottom edge of the back plane, I’m observing the angle here on his back and trying

• to imagine what it would look like of it was a box. And then it transitions to the angle

• of the side plane.

• Find the edge between the side plane and back plane. At this point it should look like a

• simple 3 dimensional form. Notice that even though he is leaning back and toward us a

• bit, were not seeing the top plane of the rib cage. That’s because the top plane tilts

• forward, so in most back poses the top plane will be hidden behind the back plane.

• The 12th rib actually connects to the spine up here and then angles downward. So, I like

• to define that edge. It’s the same edge that we ghosted in from the front view in

• the previous drawing. It’s a continuation of the thoracic arch as it curves around the

• bottom corner of the ribcage and comes back up to connect to the spine.

• Ok, this is the part that I wanted to go over. Remember in the previous video I mentioned

• that the back plane has a concave wedge that holds the spine. To cut this wedge shape out,

• we can think of 3 planes. One center plane, and 2 side planes. The center plane just follows

• the curvature of the thoracic vertebrae.

• I want to point out that this S curve is highly exaggerated by the trapezius muscles. The

• spine will curve a little bit, but the curve were seeing here is the muscle pushing

• in past the center line.

• Thoracic spine rotation does affect the rib cage, but not nearly as much as this pose

• might suggest. Ok, let’s get back to that wedge.

• On each side of this center plane, well have a inward facing side plane.

• This might just look like 4 vertical lines to you, but try to imagine the cross contour

• of this surface. This plane angles like this. And this plane angles like this. This is part

• of the back plane. And this is also part of the back plane.

• If a trail of ants marched across this surface, that ant trail would be the cross contour

• line. Around the side plane, across the back plane, down the wall of the wedge, across

• the center, then back up the other wall of the wedge, and across the rest of the back

• plane.

• Keep practicing drawing the forms until you have them memorized. If youre struggling

• with perspective, go back and rewatch my video on structure. Practice drawing boxes in perspective.

• Once you can easily draw a box, then you can start making that box more complicated by

• cutting out wedges.

• I hope you guys enjoyed this lesson! If you want to see more drawing examples go to proko.com/anatomy.

• I have 8 more examples, which serve as the answers to the assignment from the last lesson.

• Youll also find 3d models of the rib cage and the simplified rib cage, that you can

• rotate and draw from any angle. proko.com/anatomy

• If you’d like to win a free membership to the premium anatomy course, go to facebook.com/prokotv

• and share the post for this video. I’ll choose a random winner next Friday. Good luck!

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