In this lesson you’re going to learn how the jaw works in order to create an open mouth that is anatomically correct. The first step to understanding how to do this is to examine how the hinge of the jaw works.
There’s no real secret behind this – the lower jaw is just one solid piece of bone that swivels at the point where it attaches to the head right in front of the ear. When you are drawing an opened mouth, the jaw just rotates downward, but the actual shape of the jaw bone doesn’t change. Remember that the skin that sits on top is driven by how the underlying bone is positioned.
Now that you have rotated the jaw downward it’s time to add the skin and lips on top of them. The skin can stretch quite a bit, but it still does have limitations especially when you are sticking to fairly realistic character construction.
If you’re having some trouble visualizing this, now is a perfect time to get in front of a mirror and practice stretching your mouth open and taking notice of how the skin moves and what happens to the corners of the mouth as you move your jaw wider and wider. Try opening and closing several times while paying close attention.
Remember that the skin along the chin doesn’t have much thickness between itself and the bone underneath. This is why it is important to understand how the bone structure is working under the skin so you will know exactly how to draw the skin on top.
Continue to explore the opened mouth by drawing in the neck and the natural folds of skin that occur when the mouth is opened at an extreme position like this.
To push this expression further open up the eyes a bit more and change the position of the eyebrow so it is sitting much higher on the head. Adding this change to the eyes gives a very convincing look of shock or surprise to the character.