From what I've read, you don't ever really stop learning anatomy. There's no point where you graduate from learning the basics to being a good artist. Good artists are good because they've mastered the basics, the know their anatomy, value, and color really, really well, but that doesn't mean they put down the anatomy books and never make a muscle study again. No matter how good an artist is, he/she's still learning and getting better. That's what I think anyway. Loomis and Bridgeman are great to learn from, you can get bridgeman's complete guide to drawing from life, which is kind of a compilation of all his books, at a lot of bookstores, and you can find loomis' books online, They're out of print. Bridgeman's books are online too if you need them. Good luck!
How much i should learn anatomy to draw good? I found it difficult to remember those muscles and bones..