As to why someone might have a skull: I have to tell this story here, as I might never get a chance to tell it otherwise....
Back about 40 years ago, when I was in graduate school, I learned that one of my friends (colorful character, a Bohemian-starving-artist/musician type) had just moved to a different house; I thought I'd go by and visit him, to see his new digs. So I arrived, knocked on his door, and he invited me in. We sat down in the living room to chat, and I looked over at the mantle above his fireplace, and there, prominently displayed, was a human skull. Curious, I asked, "Dan, what's the story behind that skull?"
It turned out that the skull was that of his late uncle. The man had been a long-term patient at Eastern State Mental Hospital, and died there, and he was buried in the pauper's section of the cemetery on the grounds of the hospital. This had happened years before. Just after he had moved into his new lodgings, my friend had gotten a phone call, out of the clear blue, from someone at the hospital, who said, "We have your uncle's remains....where do you want them?"!
The state highway department was putting a new road through the area, and had used eminent domain to take some of the hospital property, which included the pauper's graveyard. The hospital had disinterred all of the remains which could be located, and when they were able to find a next-of-kin of a decedent, the remains were offered to that person. Dan was his uncle's only surviving relative. Being a starving-artist type, he had no spare funds to reinterr his uncle in a private cemetery, and wasn't prepared to take possession of the whole skeleton. So he told the man on the other end of the phone, "Just bring me the skull, and dispose of the rest of it." So that was how his uncle's skull ended up on the mantle.