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  • Anatomy of the Pelvis Hello, in this episode of Proko were going

  • to learn the anatomy of the Pelvis. Well explore the structure of the parts, the difference

  • between a male and female pelvis, and how to simplify the structure to make it manageable

  • to draw. Let’s take a look at the Parts of the Pelvis.

  • The Parts of the Pelvis The 2 hip bones, along with the sacrum and

  • coccyx of the spine form what's known as the pelvis. Each hip bone consists of 3 parts.

  • These 3 parts actually start out as 3 separate bones at birth and fuse together throughout

  • puberty. On the top half stands a wing-like wall called the ilium. Under the ilium, in

  • the front is the pubis. And behind the pubis is the ischium. You can remember that there’s

  • all sorts ofickystuff that happens in the ischium.

  • These 3 bones fuse together right in the middle of the acetabulum - a deep socket of the ball

  • and socket joint of the hip. The femur sits right in there and rotates in all directions

  • to move the leg.

  • Ilium The Ilium is the largest of the 3 parts. The

  • 2 curved walls converge in the back, connected by the sacrum. The part of the ilium that

  • is visible in the surface is the top edge known as the iliac crest, so let’s take

  • a closer look at it. The iliac crest starts in the front at the

  • ASIS, that’s Anterior Superior Iliac Spine . And it ends in the back at the PSIS or Posterior

  • Superior Iliac Spine. Dont miss this. I mention these two landmarks a lot. And I use them

  • a lot when drawing the figure. From top view, the crest curves outward from

  • the ASIS for a short distance to the tubercle. Then curves back for a longer distance, and

  • then almost straight backward for a short distance to the PSIS.

  • From side view, the crest creates a half circle arc. This arc shape will vary, from a smooth

  • curve in some people, to a sharp corner at the top point in other people. This high point

  • is somewhat back from center. Men tend to have a more angular high corner, while women

  • have a smoother curve.

  • Only the front 1/4 of the crest is actually visible on surface, starting from this tubercle.

  • The rest is covered by the external oblique muscle on the sides and flank fat in the back.

  • Here’s a good example where you can clearly see the ASIS in the front and the external

  • oblique covering the side portion. On a more muscular or overweight body type, it appears

  • as a sharp edge, indicating the bottom border of the external oblique. If the torso bends

  • laterally, the external oblique is stretched up, sometimes exposing the middle section

  • of the crest. On a very lean person, the ASIS pokes out as a visible protrusion. It pokes

  • out even farther when the spine is extended, and the muscles around the ASIS are stretched.

  • The visible portion curves downward and inward.

  • Try to feel it on yourself.. In the back the Posterior Superior Iliac Spines

  • are surrounded by muscles and flank fat. They are usually seen as two dimples where connective

  • tissue attached to the spines pull the skin inward. You might see a subtle indication

  • of the crest in men, though mostly softened by the flank fat. In women it can be so softened

  • that the hips appear to continue all the way to the top of the waist. In some poses when

  • a lean model stretches her back muscles, the bones push out and appear as protrusions instead

  • of a dimple.

  • Pubis Ok, let’s move on to the pubis. The two

  • sides are joined by a cartilaginous disc at the pubic symphysis. This is a commonly used

  • landmark, but you won’t actually see a bony point because it’s covered by pubic fat.

  • You can find it by following the trail of the inguinal ligament. A thin string-like

  • ligament stretching from the ASIS to the pubic tubercle just lateral of the pubic symphysis.

  • It defines the lower border of the abdominal mass called the "furrows of the groin" and

  • appears deeper in men. The pubic symphysis aligns with the level

  • of the tailbone, although this varies. In men, it’s also on the same vertical plane

  • with the ASIS. Another useful alignment, is the pubic symphysis tends to be the vertical

  • center of the whole body. In the back, the vertical center is between

  • the bottom of the sacral triangle and the bottom of the buttocks, right in the middle

  • of where the glutes meet.

  • Gender Differences The pelvis has the most divergence between

  • male and female of the entire skeleton. Mainly because a female pelvis is built to allow

  • a woman to give birth. Skelly, I’d like you to meet, Skella!

  • What makes Skelly so attracted to Skella’s pelvis? Well, the female pelvis has lighter

  • and thinner parts. It’s about 2 finger widths wider and 2 finger widths shorter than a male

  • pelvis. The walls of the ilium are more vertical, but not as tall. The pelvis is tilted forward

  • more on a female. The ASIS protrude forward more and don't align with the pubic symphysis.

  • On a man, the ASIS and pubic symphysis align on the same vertical plane.

  • You might also notice that the pubic arch is much wider on a female pelvis. About 120

  • degrees in women, but only 90 degrees in men. This means that women’s ischia are farther

  • apart. Creating a wider gap between the leg muscles because the insertion points of the

  • adductor muscles are farther. On a woman, you might see a gap even if the legs are together.

  • On a male, the gap is much smaller. Sometimes there is no gap, even if the legs are separated.

  • The widening of all these parts on a female pelvis pushes the acetabula laterally, which

  • in turn pushes the greater trochanters. These differences, along with more fat distribution,

  • account for why women have more prominent hips. An average woman will have a higher

  • body fat percentage than an average man, so the baby doesn’t starve during hard times.

  • Like the pelvis, the sacrum is also shorter, wider, and curves posteriorly more. On the

  • surface, this plane of the lower back is more angled on a woman and more vertical on a man.

  • The main reason for the wider female pelvis is to create a larger inlet and larger outlet

  • for a baby to pass through. The inlet is this round shape here. Very round

  • and wide on a female. On a male pelvis the inlet shape is more like this.

  • The outlet is the space between the bottoms of the ischia and tailbone. You can see how

  • everything is more spaced out on the female pelvis, perfect for childbirth. Allow me to

  • demonstrate. As you can see, the baby passes through Skella's pelvis quite easily. But

  • with Skelly. Well... To review, a male pelvis is characterized

  • by height, weight, more vertical angle, thickness, sharper angles, and a smaller cavity. A female

  • pelvis is characterized by width, lightness, forward tilt, thinness, and a larger cavity.

  • Simplified Structure As you can probably tell, the forms of the

  • pelvis are quite complex. Trying to imagine these forms from various angles let alone

  • drawing them is very challenging. Let’s take a look at a few ways we can simplify

  • the pelvis to make it easier to construct and pose the body.

  • The relationship between the top half and bottom half of the pelvis simplifies to 2

  • perpendicular planes. The Ilium generally angles inward to the sacrum. The ischium and

  • pubis together angle perpendicularly to that, meeting at the pubic symphysis. From the side,

  • It's kinda like a figure 8. A twisted figure 8..

  • Bucket Now, the method I’ll use a lot in this Anatomy

  • course, is the bucket.. I like it because starting the construction with a bucket allows

  • us to get very accurate placements for the landmarks.

  • A bucket is basically a tapered cylinder. This cylinder, in a neutral standing pose,

  • is tilted forward, like the pelvis. It's wider at the top and narrower at the bottom. Also,

  • the width is longer than the depth. So the top and bottom caps are not perfect circles.

  • This ellipse of the top cap is the first thing I draw. It determines a lot of things. The

  • width, the forward tilt, and the side to side leaning. It's also not too hard to find on

  • the surface of a model. From the front, use the ASIS points to determine the side to side

  • leaning angle. Now, from the top you'll notice that this ellipse doesn't really follow the

  • shape of the iliac crest all the way. It does for this middle portion but then the crest

  • takes a sharp turn inward, leaving this extra space.. Well, if you consider the muscles

  • and flank fat in this area, this ellipse actually follows the surface curve nicely! And in the

  • front, the curve follows the form of the abs. Of course, on an obese body, this won't work

  • as well. So, were looking just at this portion of the iliac crest when drawing the

  • top ellipse. After I've established the ellipse, I'll add

  • the side planes. The length depends on how much foreshortening there is caused by the

  • tilt and our point of view. Longer lines when there’s no foreshortening. And shorter lines

  • when there’s a lot of foreshortening. You also have to think about the gender differences.

  • Remember, a female pelvis is wider and shorter than a male pelvis.

  • Finally, I'll add the bottom cap and that gives me a simplified form for the pelvis.

  • There we have a simple representation of the pelvis as a bucket. In the next lesson, I’ll

  • show you how to break it down further to construct the minor forms of the pelvis. In the meantime,

  • fill a page with buckets from various angles. Premium Anatomy students, you can login to

  • your account and use the 3d model of the bucket and pelvis as reference. Spin it around and

  • draw the bucket! If you’d like to sign up for the Premium Anatomy Course, go to proko.com/anatomy

Anatomy of the Pelvis Hello, in this episode of Proko were going

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骨盤の解剖学-アーティストのための (Anatomy of the Pelvis - for Artists)

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    vulvul に公開 2021 年 01 月 14 日
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