Step 10: Lightly sketch the eyeballs inside the head as two small circles. Use the initial lines as guides for placement. The Jack Russell terrier's head is tilted, so the eye on the right will be higher. When you get the size and placement of the eyeballs right, darken the lines. Use a series of quick, short strokes around the eyes for the fur. Add a few more lines around the circles to create the outer shape of the eyes.
Step 11: Inside each eye, off to the side, draw a tiny circle to represent glare. In the middle of each eye, draw a big dot for the pupils. Shade in the rest of the Jack Russell terrier's eyes. Don't overlap the tiny glare circles. As you shade the irises, use a value that's slightly lighter than the pupils. You can also make the top portion of the iris a bit darker than the bottom. Add a few quick, short strokes to emphasize the fur on the dog's brows.
Step 12: Draw the Jack Russell terrier's nose inside the muzzle by first lightly sketching a small oval. Place the nose on top of the bottom, right edge of the head circle. Darken the sides of the oval and curve the lines inward to create the nostrils. Draw a small vertical line at the bottom of the nose and use quick, short strokes for the fur at the top. Darken the rest of the oval and add an extra pointy line at the bottom.
Step 13: Draw the mouth under the nose using a series of quick, short strokes. The mouth should consist of a sloping line that's broken up. Draw quick, short strokes along the basic path of the small circle to create the muzzle. The left side of the muzzle should be a bit wider than the initial circle. The longer you make these strokes, the shaggier the Jack Russell terrier's fur will be. The strokes on top of the muzzle should overlap the eye on the right a little bit.
Step 14: Use the triangle-like shapes on the head as guides to draw the Jack Russell terrier's ears. Darken the basic path of the initial triangle but make the shape more curvy and wavy. Darken the visible portion of the dog's other ear as well.