Terry, I don't know if it's how the picture is lit as much as it's the context it's in. I find things wrong when I post a photo of my drawing here that I didn't see in the photo of the drawing on my computer. IMHO, we just have to sharpen our awareness so we see the details before someone has to bring them to our attention. That's what my aim is, anyway. Till then, I'm grateful for those who bring things to my attention. I hope having stuff pointed out to me and then seeing it will help me focus on such things on my own. Sort of like training wheels before you learn to ride a bike, you know?
As for anatomy, the bone and muscle structure under the skin on an animal or human matters a lot. That's why artists study anatomy. I think squirrel anatomy is probably close enough to dog and horse anatomy that I can picture the main features. Whether I can reproduce them accurately is another story. But at least I have an idea, especially of how horses are built. Maybe before you do an animal, study the skeleton and muscles if you can find a site that has a picture of that. Or, if you have a pet dog or cat, just pet it and think about how it's built, where you feel the bones protrude, which way the legs are bent, etc.
I'll tell you a funny story about that. My mom went to art school, and she had to study anatomy, which she hated, she told me. But I bet it was just human anatomy.
Every Christmas, she used to make our Christmas cards, usually a linoleum block print. One year, she made the block with Joseph leading a donkey, Mary riding it and holding the baby Jesus. I was old enough that I had already studied horses and tried to draw them,
so I was appalled when I saw the picture she planned to use for the block print had the donkey's hind legs bent the wrong way! They worked like knees instead of hocks. I pointed this out to her, and at first, she didn't want to believe me and wouldn't change it, but I persisted. I brought her a bunch of photos of horses in my books and from my horse scrapbook and insisted. Finally, she changed the donkey's hind legs. Whew! Major meltdown on my part averted!
For me I see the drawing the same in my post as I see on my PC but it's way different then my B&W print out. That's why I thought a back light would emulate a PC screen but I can't find what I'm looking for.