Step 15: Use the initial half-circle as a guide to draw the top of the head. Follow the curvature of the guide as you draw the front part of the head but make the line a bit bumpier. Above the brow, draw another bumpy line for the back of the T. rex's head. To the left, draw yet another bumpy line along the path of the guide for the brow on the other side. Inside the head, near the left side, draw a small oval-like shape for the nostril.
Step 16: Use the initial curved line at the bottom as a guide to draw the shape of the Tyrannosaurus rex's jaw. Follow the path of the guide but make the line a bit wavier. Add a few lines under the mouth too.
Step 17: Darken the initial lines that connect to the body to create the neck. Add a few lines inside the T. rex's neck for the side of the head and extra detail like veins.
Step 18: Use the line that's shaped like a 7 as a guide to draw the first arm. Follow the path of the guide and lightly sketch the shape of the arm around it. Use a series of curved lines as you draw the shape of the arm for the muscle structure. When you get the shape of the arm right, darken the lines. The Tyrannosaurus rex's fingers point backward, so just draw a pointy shape on the right side at the bottom.
Step 19: Use the short, angled line under the neck as a guide to draw the other arm the same way. First lightly sketch the shape of the arm around the guide. When you get the shape right, darken the lines. The fingers are folded and point to the back. Draw a pointy tip on the right side of the shape.