As an artist - especially a portrait artist - you have to become very familiar with the human skull. It is the foundation of the face. If you are ever going to accurately capture someone& likeness, you need to understand what lies beneath their skin.
tricyclesinskirts: Henry Gray’s Anatomy of the Human Body: Posterior surface of the forearm, superficial muscles. Note how there aren’t any muscles in the fingers. Your fingers are controlled by tendons that connect to muscles in the forearm.