When we refer to the drawing of the mouth, generally, its external view is depicted, that is, the lips. Nonetheless, when representing facial expressions, also the gums, teeth, and all of the internal part are to be emphasized.
Front
Step 1- Divide a horizontal line into four parts. Above and below this line, by its middle point, draw two inverted triangles.
Step 2- Draw an “M” above, and then a small “V” below the interlabial line.
Step 3- Close the lips, drawing a “C”, and begin the shading with the color scales. Round the figures following the form of the lips. The edges are darker.
3/4
Step 1- Draw a horizontal line, divide it into four equal parts, and remove one of them. Draw two inverted triangles, one being larger than the other.
Step 2- Draw an “M” above, and then a small “V” below the interlabial line.
Step 3- Close the lips, drawing a “C”. In the upper lip, the point of light stays in the central part, and there are darker tones than in the lower lip.
Profile
Step 1- Draw a horizontal line, divide it into four parts, and remove two of them.
Step 2- Draw a rounded form for the lower lip. A side view shows the upper lip above the lower one and projected forward.
Step 3- Work the shading with the color scales, where the light tones are overlapped by darker ones, gradually.
The movement of the muscles of the face alter both the shape of the lips and the facial expressions.
Take a mirror and watch the movements that you make with your lips. This is a way to study the design of the mouth.