Previously on Proko..
Skelly sees Skella.
It’s love at first sight.
He tries to seduce her with questionable pickup lines.
She’s not impressed.
He gives her a flower.
They hug.
Skelly gets pregnant!
Skella pulls a rib, they swordfight!
Stan has bones too!
This week, there’s drama in the Proko house.
The new episode starts now!
Hello!
I’m Stan Prokopenko, you’re watching Proko.
We've already studied the spine, pelvis and rib-cage.
This lesson on the shoulder girdle, will complete the bones of the torso.
Very soon we’ll move on to muscles!
Simple Structure of the Clavicle
Let's begin with the clavicle, because that's where the shoulder begins.
A clavicle in its least foreshortened position, is about one cranial unit… more or less,
which is about the same length of the sternum... more or less.
That's the advantage of having them near each other on the front.
They're convenient to compare.
But unless we're looking at the chest from the front, one of these is likely to be foreshortened.
So we need to think of clavicles as fore-shortenable sticks
4 shorten-able sticks?
What?
No!
No Skelly...
They are FORE-shortenable.
Meaning, they can be foreshortened.
But a clavicle is not a straight stick.
It has three parts, and they are offset like this:
In fact, when you put them together, they make the shape of a Cupid's bow
If love is not your thing, the clavicles also look like a pair of bicycle handlebars.
And since they wrap around the base of the neck like the collar of a shirt, we call them
collarbones.
That's the first bone of the shoulder girdle: the clavicle.
Simple Structure of the Scapula
Now let's move to the dominant bone of the shoulder girdle: the scapula.
The scapula is also known as the shoulder blade.
We can simplify it as a triangle that's about a cranial unit high, and about a cranial unit
wide, and when the scapulae are in the neutral anatomical position, they are about a cranial
unit apart… more or less.
Here's a comparison that may help.
The scapula is about the size of a cupped hand, which conveniently matches its concavity
to the convexity of the rib cage.
The scapula is all one bone, but for artists, it has two distinct sections.
The body of the blade is here, mostly deep below the surface, except this medial ridge.
The spine of the scapula is almost a bone of its own.
It sticks out like a trowel handle that you can tap along the surface.
That's the spine of the scapula…
Sub-cutaneous and super-important.
Now, when we combine the scapula and clavicle, they sit on the rib cage like shoulder pads.
The rib cage is thinnest at the top end, but with the shoulders, the thorax is widest at
the top.
The shoulder girdle is usually bigger in men than women, though it might not give any advantage
in a fight…
Anatomical Details of the Clavicle
Where do you think the arm begins?
No, ‘dog’ is not the correct answer.
The arm begins at the pit of the neck!
This is the only bone-to-bone connection of arm to the trunk.
The rest of the shoulder girdle never touches the rib cage - a network of muscles lies between
them and secures them together.
The pit of the neck is simple, but it has some pit-falls... sorry.
You may know that the sternomastoid tendons make a V shape in there, but only when they’re
tensed, and they’re not always tensed.
Watch for a box-shaped pocket…
Don't place them too close together.
Clavicles don't touch each other.
They attach at the corners of the manubrium, spread out a good two-fingers-distance from
the center.
An eyeball could fit in there.
Ligaments strap the clavicles to the sternum.
They allow it to rotate on its ellipsoid joint, and smooth out the bumpiness.
So this area is usually smooth.
Clavicles are subcutaneous all the way across.
They anchor muscles from the neck and chest, and serve as very important landmark lines.
Anatomical Details of the Scapula
When we get to the end of the clavicle, we reach the Acromion Process.
It seems like an extension of the clavicle, but it’s actually an extension of the scapula
- the furthest reach of the spine of the scapula.
The acromion process is a flat rectangular platform that "steps down" from the clavicle.
The spine on a human scapula twists from back to top.
This means the spine of the scapula is a complex plane, like a ribbon on a cylinder.
This may be hard to draw, but it's valuable.
That rolling plane affects the surface, and helps an artist know how the light changes
as it twists.
Now, here's the super important thing about the scapula.
The blade, specifically this medial border, and the spine are the primary landmark lines.
They make a fixed angle, more than 90°, and when the scapula moves, that angle stays fixed...
So, how the heck do we find these lines on a model?
Where’s the scapula in this crazy mess of bumps?
A lot of the scapula is covered with a mesh of muscles, but these lines will always be
visible.
In some poses, especially on muscular or heavy people we’ll see them as indentations.
The trapezius attaches along the spine of the scapula.
Rhomboids attach along the side.
A group of scapular muscles sit on the inside of the blade.
And the deltoid attaches along the bottom of the spine.(NEED TO RERECORD) In other poses
and especially on very lean people, the bones project outward, since the volume of the muscles
is thin or stretched.
Motion
Before we look at motion, let's ask why we even need a shoulder.
Why do we even need a shoulder?
Well, obviously to move our arms, which place our hands wherever they should be... or shouldn’t
be.
An arm stuck to a ribcage couldn't do much beyond flopping around.
A scapula allows movement because it has a ball & socket joint.
The head of the humerus is the ball.
The Glenoid Cavity is the socket.
The Glenoid Cavity faces the front.
The ball of the humerus faces the back.
That means we can move our arms forward more easily than we can move them backward.
Most people can lift their arms up to about level without moving the shoulder blade...
much.
That's called Glenohumeral movement.
If we extend laterally or anteriorly it eventually reaches its limit when the humerus hits the
acromion process.
That means the higher we raise our arms, the more the shoulder girdle does the work.
When the scapula moves on the thorax, it’s called Scapulothoracic movement.
Here's how it works.
Lateral rotation brings the corner of the blade out toward the side.
Medial rotation brings it toward the middle.
Elevation lifts the shoulder straight up.
Depression brings it back down.
There's very little room for depressing the shoulder from the neutral position.
Protraction slides the scapula forward around the rib cage.
Retraction slides it back around the rib cage.
Finally, there’s Anterior and Posterior tilting.
If you’re one of those weirdos that likes to scare your friends by popping your shoulder
blade out, then you are experienced Anterior tilter.
Stop that please…
It’s scary.
We can also combine movements and roll the shoulders around.
But it's not just the scapula moving.
The clavicle comes along for the ride.
They’re connected by ligaments at the plate joint, but there's a little play between them.
Each clavicle rotates independently from the other at Sternoclavicular joint.
So, pay attention to the angles of the clavicles and look for motion there too.
Motion
The Motion of the Scapula.
Oh no!
We’re out of time…
Well, to learn about the impressive motions of the scapula, head on over to proko.com/anatomy.
In the premium anatomy course, each lesson has extended videos, more drawing examples,
and 3d models that you can rotate and draw from any angle.
Really check it out!
I’m very proud of the premium course.
Assignment
First, draw the ribcage.
Then, draw the shoulder girdle on top of the ribcage.
Draw around to the other side, ghosting it as it goes around.
Look for angles and landmarks, and draw them as three-dimensional forms.
We’ll need to master this before we include muscles.
Think about it - the positions of the bones determine the shape of the muscles.
When we can draw the clavicle and scapula as forms, we have the underlying structure
that shapes the shoulders.
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