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  • Ribcage

  • Hello, welcome to Proko my name is Stan Prokopenko. So, were done with the pelvis and now were

  • going to move our way up to the rib cage. In this episode well learn about the simple

  • structure of the rib cage. Then look at some of the detailed anatomical parts.

  • Simplified Structure

  • The rib cage is often simplified as an oval shape. For a gesture drawing, that’s good

  • enough. But for an anatomy study, it’s not. The rib cage is more like an egg because the

  • top is narrower than the bottom. And more specifically, the rib cage is more like an

  • egg with planes. It has clear front, side, and back planes. The front plane is composed

  • of the sternum and costal cartilage. The front plane transitions to side plane right where

  • the costal cartilage connects to the ribs. From there the ribs continue backward in a

  • subtle convex curve. Then they reach the angle of the ribs where they take a sudden turn

  • medially for the back plane. The back plane actually has a concave wedge where the ribs

  • curve forward to connect to the spine.

  • This is unique to humans, allowing us to lie on our backs comfortably. Quadrupeds like

  • dogs and horses have pointed spinesthe spinous processes of the vertebrae extend

  • way up. That might explain why Skelly’s always being so lazy!

  • Now don’t miss this. The top plane actually slants forward. From side view, you can see

  • how the rib cage connects to the neck at this angle. The neck curves back to hold up the

  • head vertically. Ignoring this will result in the infamouslollipop neck’. It tastes

  • good. But it doesn’t look good.

  • Oh, the bottom plane. It’s complicated. It curves. In the front, from the bottom of

  • the sternum, the costal cartilage angles outward creating the upside down V shape called the

  • thoracic arch. The cartilage of the 10th rib has a sharpcorner of the ribcage”, which

  • you can see and feel on the surface. From that corner, the bottom plane curves around

  • to the back and then up to the 12th thoracic vertebra.

  • Parts of the rib cage

  • The Rib Cage is made up of the thoracic vertebrae, which we already covered, twelve pairs of

  • ribs, each connected to a vertebra, the costal cartilage, and the sternum.

  • Do we really need to know how many ribs there are?”

  • It may seem like overkill, but when you invent poses or sculpt the figure, you may want to

  • know where to attach the muscles of the torso. The rib cage is an origin and insertion area

  • for many muscles. So, let’s learn the ribs so we can attach the muscles in the right

  • place.

  • But there’s so many of them!”

  • Well, not really. Only 12. But don’t worry, if you understand the simple structure of

  • the planar egg and the general pattern of the ribs, youll find it easy to place the

  • ribs in that egg structure.

  • From the back, the ribs angle down slightly. As they reach the side plane, they dive diagonally

  • at about 45 degrees and stay at that angle until they reach the costal cartilage in the

  • front. The costal cartilage of the top half stays close to horizontal. The bottom half

  • curve upward toward the sternum.

  • Do women have an extra rib?”

  • Nope! There is an abnormality in a very small percentage of people who have an additional

  • cervical rib (that’s in the neck). This happens more often in females, but also occurs

  • in males.

  • So what parts of the rib cage show up on the surface? On a muscular person when the muscles

  • stretch, we see some of the lower ribs in the front and also in the back.

  • On a lean person it doesn’t take much of a stretch to reveal the ribs in the front

  • and back, and theyre much more obvious.

  • I’ve invented this x-ray pad to help us. With some x-ray paint and a simple canvas

  • I was able to jerry-rig one of these bad boys! Cool huh?

  • Now, how do we figure out where the rib cage is in poses where we can’t see the ribs?

  • Well, we can use our knowledge of where the muscles attach. Rib number 5 is an important

  • one. The bottom of the pec aligns with the level of 5th rib. The first digit of the external

  • oblique originates at the 5th rib. And the first visible digit of the serratus originates

  • at the 5th rib. The 3 most prominent serratus digits originate at the 6th, 7th, and 8th

  • ribs.

  • Costal Cartilage

  • The Costal Cartilages connect the ribs to the sternum. They also make the ribcage more

  • flexible and elastic.

  • On a very lean person with thin pec muscles, youll see the first few costal cartilages

  • connecting to the sternum in the front. A bit lower and to the side, the muscle and

  • breast tissue (on a female) will cover the ribs even on a very lean person.

  • The lower front edge of the rib cage is the Thoracic Arch. It’s made up of the cartilages

  • from the 7th to 10th ribs. Starting from where the Costal Cartilages of the 7th ribs attach

  • to the Sternum, down to the corner of the 10th rib. This corner often stands out in

  • the figure, especially when the model is inhaling or leaning back.

  • Because the thoracic arch is made of cartilage, it will have more variation than bone. Artists

  • tend to idealize this shape to be 90 degrees on males and a narrower 60 degrees on females.

  • And, a more masculine arch will curve outward and a feminine arch will curve inward.

  • But the shape of the thoracic arch is more of an idealization than a rule. In this example

  • we can see a wide arch on a female.

  • Sternum

  • Also known as the Breastbone, the Sternum is made up of three pieces and looks like

  • a downward facing dagger or necktie. You can think of these pieces like the sword of a

  • Roman Gladiator. The top piece is the Manubrium, which meanshandle’, the Body is the

  • Gladiolus which means blade, and the tip of the sternum is called the Xiphoid process.

  • Xiphos, means sword.

  • The top corners of the Manubrium are where the clavicles attach, forming the pit of the

  • neck.

  • The body of the sternum is the longer bone, thinner at the top and thicker at the bottom.

  • It’s about twice the height of the Manubrium. On a male, the lower end of the Body is usually

  • located below the nipples and above the level of the lower border of the Pecs. On a female,

  • the placement of the nipple and bottom of the breast varies greatly.

  • At the lower tip of the Sternum is the Xiphoid Process, or the dagger! It’s about the size

  • of the tip of your thumb. Sometimes the xiphoid process sticks out from the surface, and sometimes

  • it digs in and makes a depression, surrounded by thick costal cartilage.

  • Check out proko.com/anatomy for extended anatomy lessons and more examples of the assignments.

  • That’s proko.com/anatomy

  • Assignments

  • For our assignment this week, let’s build on the assignment from the Spine lesson. Now

  • that we know more about the structure of the pelvis and rib cage, we can do a more precise

  • version. Construct a Robo Skelly rib cage and the pelvis using the bucket method. Try

  • to be as accurate as you can with them. Don’t just draw a generic rib cage shape in there.

  • Look for clues from landmarks and muscle attachments that will tell you exactly where the rib cage

  • is. I’ve uploaded a bunch of model photos, which you can find in the description below.

  • That’s it, thanks for watching! If youre posting your drawings, use hashtag #proko

  • and don’t forget to follow me on Facebook and Instagram. If you like this video, share

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Ribcage

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B2 中上級

肋骨ケージの解剖学 - アーティストのための (Anatomy of the Rib Cage - for Artists)

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    vulvul に公開 2021 年 01 月 14 日
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