Your assignment is to analyze these images and draw them as simple form. Show that you understand the basic structure of the joint types. Marshall will demonstrate these images after the new year.
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The premium version of this lesson includes an extended video, assignment demonstrations, an eBook, and a 3d Model of Robo Skelly that you can zoom and rotate in your browser.
Hey welcome to another lesson on Proko. This lesson is about the types of joints in the human body.
As artists we really only need to learn the synovial joints, like the shoulder and knee, because they move. Joints that are fibrous and cartilaginous hardly move, and some, like the connection of the two pubic bones, don’t move at all. When you’re learning how to draw, pay attention to synovial joints, and keep your thoughts away from pubic bones.
If you know where the hinge joint is on this foot, you know that it won’t do this or this when you stand on your toes. It will do this. We need to know the position of that hinge joint to make squash and stretch look like the real thing.
There are 6 types of synovial joints. They have varying shapes, but the important thing about them is the movement they allow. Joints determine what positions our bodies can take. We learn them to invent poses. And we learn the limits to stretch the limits.
The 6 types of synovial joints are: Hinge, Pivot, Ball & Socket, Ellipsoid, Saddle, and Plane. Let’s go through them one by one.
Going back to the terminology from last week, the hinge joint allows flexion and extension. That’s it! Thats all it does, but it does it well. Like the hinges on a door, allow it only to open or close. The best example of it is the elbow.
So if the elbow only allows flexion and extension, how is it that we are able to twist the forearm? Well, let’s take a look at the next joint.
And by the way, the distal joint of the ulna and radius is also a pivot joint. The combination of the pivot at the top and at the bottom creates that twisting motion for pronation and supination.
Ball & Socket
The two ball and socket joints of the body are at the hip and the shoulder. The hip has a deep socket, which gives it stability, but limits some range of motion. The shoulder joint has a shallower socket, which gives it greater range of motion, but takes away some stability. Maybe that’s why a dislocated shoulder is so common.
The ball, or oval head also slides inside the socket. When it rotates along the wider plane, it slides to stay inside the socket.
A great example of an ellipsoid joint is the wrist, aka radiocarpal joint. The group of carpal bones rotate inside the socket of the radius.
The legs of the top piece, which wrap around the body of the bottom piece allow a rotation this way. The body of the top piece can glide inside of the legs of the bottom piece.
So, this unique structure allows the joint to flex, extend, abduct, adduct, circumduct, and very slightly rotate.
An example of a saddle joint on the body is the carpometacarpal joint of the thumb.
It’s basically two flat-ish surfaces, one on top of the other. These surfaces can glide or rotate.
They usually come in groups, like the carpals of the hand and the tarsals of the foot. Ligaments hold these bones together, but might allow some rotation and gliding.
Another plane joint is the acromioclavicular joint. That’s the one between the clavicle and acromion process of the scapula. When we elevate the shoulder, the angle in here will adjust to keep the scapula vertical.
I mentioned in the beginning that cartilaginous joints are not important for artists, except in one, big, important case: your spine. We’ll talk about that, in the next lesson.
For this lesson, there’s two assignments.
- Find these joints on yourself and study the movement.
- I’ve posted 6 close-up images of Skelly’s joints in the description under this video. Your second assignment is to draw them as simple versions. When you try to put them into perspective, you may find it difficult, but I will have Marshall help you understand how to do it. Post your drawings in the facebook group, at facebook.com/groups/anatomy4artists. Marshall, the perspective master will help to critique your assignments in the facebook group. Later, Marshall will do a demo to show you how to simplify your forms and move them around.
This week I’ve included another PDF ebook showing which of the 6 types every joint in the body is classified as. And again it’s shown visually, rather than just a list, so you can print these out as reference. proko.com/anatomy.
Another premium feature you’ll see this week when you login to your account, is a 3D model of Robo Skelly. This is a skeleton with simplified forms. Simplified forms are a lot easier to understand, to remember and are more practical to apply to your drawings. So, you can zoom in and rotate around Robo Skelly directly in your browser. This will help you with the assignment this week and upcoming lessons when we study the skeleton in detail.
To get all the premium features, go to proko.com/anatomy