A Tibetan engraved skull or Kapala are embellished with silver and semi-precious stones and is commonly used as a ritual bowl to drink blood out of; performed at ancient human sacrifice rituals. I want one.
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's likeness, you need to understand what lies beneath their skin.