Step 15: Draw the gorilla's top row of teeth near the top edge of the mouth. First draw the long canine on the left as a triangle-like shape. Now add the four smaller teeth to the right. These are curved at the top and flat at the bottom. Draw the other triangle-like canine on the right side. Draw a small, thin shape to the left of the right canine to represent the molars in the back.
Step 16: Draw the bottom row of teeth near the bottom edge of the open mouth. First draw the triangle-like canine on the left. Then add the four smaller teeth to the right of it. Add another small triangle-like shape on the right side for the gorilla's other canine. Draw a couple of round shapes above each canine for the molars in the back of the mouth.
Step 17: Draw a series of lines on the right side to close up the shape of the gorilla's mouth. The outermost line should go from canine to canine. Then add a few more lines for the folded skin.
Step 18: Add a few more curved lines within the mouth for extra detail . Draw an extra line on the left side and a big curved line in the middle for the gorilla's tongue. Add a few more lines above the tongue for the roof of the mouth and some below the tongue too.
Step 19: Draw the hairline on the face using a series of quick, short strokes. Start the hairline at the top, above the eyes. Then draw it downward toward the sides of the mouth. The shape should be wider at the top around the eyes and narrower at the bottom arround the mouth. Draw the gorilla's chin at the bottom by following the path of the initial arc. Use shorter strokes as you draw the chin. Follow the basic path of the arc and use quick, short strokes to create the jaw line.