Week Two
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Welcome to Day THIRTEEN of class!
The shoulder girdle is a set of bones which connect the arms to the larger structure of the human skeleton. It consists of five bones, two scapulas, two clavicles, and the manubrium.
This is a very important area to study as an artist, as the shoulder and neck area are a complex interlocking system, and each piece needs to be in its proper place in order for your drawing to look correct. It is always very obvious, even to a laymen, when the shoulder girdle has been improperly applied.
The top view is the best way to understand the shape that these bones create as they warp around the forms of the torso. The clavicles start at the center of the chest next to the manubrim and slope backwards to meet the scapula.
Make note of the red circle that shows that at the end of the clavicle sits right next to what is known as the Acromion, a lip that curves over the top of the shoulder to anchor the scapula and provide the support to both the shoulder joint and the larger over-all structure of the arm. From the front view you can see just how small this lip is, as well as how the clavicles attach to the manubrium.
Additionally, the top view shows the width and the curve of the scapula, which is almost impossible to see from any of theses other points of view. The acromion is just one small section of what is known as the spine that can be traced back along the entire width of the scapula.
The scapula is relatively large considering that the actual square space of the joint is so small - see the next page to get a better view of it - but it's purpose is two fold. The first purpose is to be an anchor for the shoulder joint, as well as to provide a lot of surface area for muscles and ligaments to connect to which is what gives the shoulder joint its flexibility.
The trade off is that this joint is very flexible, but it is also very weak. This means that this joint is prone to dislocation when pressure is applied anywhere but it's natural range of motion. In fact, the shoulder is the most commonly injured joint in the body due to how small the joint is. Any stability it does have is created by muscle rather than bone.
From the outside view we can actually see where the joint is, this is where the arm connects to the torso. The 3/4th view provides us with more context as to how shallow the joint really is. As I mentioned this is why we require such a large structure for such a small joint. The scapula provides the muscles and ligaments in the shoulder something to connect to.
One other structure that you can see in this set of drawings is the Coracoid Process, indicated by the arrow. It is a hook-like bone that juts out towards the front of the scapula, or in towards the center of the body. It's important to note that this is not the acromion, and it does not meet the clavicle. The coracoid process is a separate bone that simply provides the joint with a little more structure, as well as additional anchoring points for muscles and ligaments surrounding the shoulder joint.
The Clavicle
Here we can take another look at the shape of the clavicles, or the collar bones, independently from the shoulder girdle. You might notice that they are reminiscent of the shape of handle bars on a bicycle. This is a very common way to describe the shape, and it is an accurate comparison. These points of view, from the front, side, back 3/4, and the back help to portray the over all shape.
The main function of the clavicle is to elevate the shoulder joint and the shoulder blade away from the structure of the rib cage so that the arm has the maximum range of movement possible. The clavicle also serves the function as a sort of "crunch zone" to help protect the upper arm from injury and transfers the impact to the clavicle rather than the arm itself. Due to this, the clavicle is the most common bone to break in the human body.
The Clavicle is also one of the bones that has the most variation from person to person, in shape, size, and strength. In most people, the left clavicle is more often longer and weaker than the right.
The shoulder girdle is a complicated structure that will take some time to really study and understand, so don't get too frustrated with yourself if you are still scratching your head. The best way to get more familiar with this area of the body is to do additional studies based off of 3D models, and images of the human form in action.
ASSIGNMENT ONE
We had a lot of examples for you to study from, but for today's assignment I just want you to draw the first example of the whole shoulder girdle from the front, back, and from above. If you have time, you can take a closer look at the rotated scapula and clavicles, but it is not required.