Step 15: Darken the guides on the left side to create the tortoise's neck. Add a few extra lines along the way for the loose skin.
Step 16: Using a series of short, curved lines, draw the thick tail on the right side.
Step 17: Draw the tortoise's legs on the other side of the body by using the remaining lines as guides. Lightly sketch the shape of the leg as you follow the guide, then darken the line when you get the structure right. Don't forget the claws! The other hind leg is hiding behind the leg on this side, so only draw a small portion of it.
Step 18 (optional): For a cleaner look, erase as much as you can of the initial guide lines. Don't worry about erasing all of the guides. It's okay to leave some behind. Re-draw any final sketch lines that you may have accidentally erased.
Final Step (optional): Add some shading to your tortoise drawing to give it more dimension and volume. Pick the direction of the light source when shading so that the shadows are consistent with it. Add the value lightly at first, then gradually build up to the level of darkness that you want. Vary the pressure on your pencil to get different degrees of tonal value.
Add a cast shadow underneath. This helps ground the tortoise so it doesn't appear to be floating. Use a darker value near the middle of the shadow and a lighter value along the edge for the shadow's diffusion.
You can add more value throughout your tortoise drawing for more detail. Tortoises are brownish-gray all over, so use a single value to cover the shell and body. Don't worry about shading too smoothly. The rough value creates a wrinkly texture. Shading can be time-consuming, so be patient and take breaks. You can split up the body and shade a section at a time to divide the time adding the value. It's always a good idea to use reference for a more accurate drawing. Remember to pause the "How to Draw a Tortoise" video after each step to draw at your own pace.