This exercise comes in handy when drawing people. It helps a lot when trying to understand how stuff moves and looks when you see it from the inside.
I know it's not really a tutorial but I didn't find a better category.
Feel free to study and/or reference from it, but I would advise you to practice from medical diagrams, as this is not 100% accurate, but works well for the purpose of practicing drawing people.
Even though the names are in Spanish it should still be helpful for you