Step 15: Use the remaining shapes and lines as guide to draw the rest of the head. Darken the path of the initial circle to create the bony top part of the head that was likely use as a battering ram. Add a few more spike-like shapes inside the pachycephalosaurus's head to emphasize the armor.
Step 16: Use the first line from the left under the body as a guide to draw the first arm. Follow the path of the guide as you draw the shape of the arm around it. Sketch lightly at first. When you get the shape right, darken the lines. Use curved lines for the dinosaur's muscles. At the end of the arm, draw a series of short V-shaped lines for the digits.
Step 17: Use the short line on the right as a guide to draw the other arm the same way. Draw the shape of the arm around the guide and add the digits at the bottom.
Step 18: Use the rightmost line as a guide to draw the first hind leg. Follow the basic path of the guide and lightly sketch the shape of the leg around it. Make the top part of the pachycephalosaurus's leg thick and then gradually make it thinner toward the bottom. Bend the shape of the leg where the guide is bent for the joints. Use curved lines for the muscle definition. When you get the structure of the leg right, darken the lines. At the bottom, draw a couple of shapes similar to less-than signs (<) for the toes.
Step 19: Use the final line under the body as a guide to draw the pachycephalosaurus's other hind leg. Follow the path of the guide as you draw the leg around it. Pay attention to the joints and how the leg bends. The dinosaur is charging forward, so the leg is raised. Therefore, only draw the visible bottom half.