I wish I could recommend a book of anatomy for artists but I can't. There are a few passable books on the subject but no great ones. Some of the manga books are good for cartoony girls' anatomy, some of the older books are good for illustration reference, but no book I know of discusses the human body the way it really is.
Where a lot of books fail is that they rely on simplified muscle charts like the one above. Nobody has a split calf like the one in the drawing above. I'm sure the drawing is accurate but in real life some additional muscles, ligaments or fat must cover the two parts of the calf and make them seem like one.
Look at the drawing of the sternomastoid muscles on the left, above. According to the drawing charts they form a big "V" in the neck. You can only see half of them here but you know what I mean.
Now look at the photo on the right (above). The "V" is clear enough when the neck is normal but when it's strained as it is in the picture, or the face grimaces, the V becomes an "A." That's because muscles the drawing doesn't show cover the sternomastoid and they also have an influence on the way the neck looks. The muscle charts are incomplete. They leave out muscles just to have a tidy drawing.
Do you disagree?