Step 10: Use the bottom part of the initial half- circle as a guide to draw the top of the mouth. Follow the basic path of the guide and lightly sketch a wavy line below for the mouth. When you get the shape of the T. rex's mouth right, darken the line.
Step 11: Draw a series of V-shaped line under the mouth for the teeth. Start drawing the T. rex's teeth in the section that's below the eye and move toward the left. Make the teeth near the middle bigger than the ones on the sides. On the left side, draw a curved line for the other side of the T. rex's mouth and add teeth under it too.
Step 12: At the bottom, lightly sketch a wavy line that's has the same slope as the guide line for the bottom part of the mouth. Notice the distance from this wavy line to the guide at the bottom. Don't draw it too close. When you get the shape right, darken the line. This line should meet the corner of the mouth at the top. Draw a series of triangle-like shapes along the path of the Tyrannosaurus rex's mouth, on the left side, for teeth.
Step 13: Draw a few more triangle-like shapes on the left side for more teeth in the T. rex's mouth. Lightly sketch a short, curved line and add more teeth on top. Now draw a curved line that connects to the top of the mouth. Use the initial sloping line on the left as a guide to draw this connecting line.
Step 14: Inside the mouth, on the right side, draw a curved line for the skin that connects the T. rex's jaws. Inside the mouth, draw the tongue using a couple of curved lines that slope to the right.