Step 10: Inside the muzzle, near the tip, draw a small shape similar to curved oval for the mule's nostril.
Step 11: Under the nostril, draw a line that curves upward for the mouth. Make the tip of the mule's mouth thicker. Draw a curved line under the mouth for a bit of loose skin.
Step 12: Darken the top part of the initial arc but make it flatter to give the muzzle more shape. Draw a couple of curved lines under the mouth for the mule's lower lip and chin. Stay inside the shape of the arc.
Step 13: Darken the arcs on the head but make the lines wavier to create the mule's ears. Draw a few wavy lines inside the arcs for the ears' openings and for some wrinkles. The ear on the right should be a bit smaller because it's on the other side of the head.
Step 14: Use the initial circle and arc as guides to draw the rest of the head. Darken the outer edges of the guides to create the shape of the mule's head. Make the top part angular for the brow. Make the bottom part of the muzzle a bit thinner than the initial arc. Curve the left side of this line up to create the strong, round jaw. Curve the left side of this line up to create the strong, round jaw. Draw a series of short strokes inside the head to help define the shape and muscles.