The Hand of Osiris was a fictional artifact sought by the Cult of Osiris, which brought them into conflict with the Venture Family in the episode Escape to the House of Mummies Part II. It was never actually shown, and its fate is set aside in the plot to focus on Dr. Venture's contest with Dr. Orpheus to find the better way to shrink people.
At some point, the Hand was in the possession of the Ventures, whom they foolishly let Caligula hide. He chose to hide it inside his butt. Later, Edgar Allan Poe came to possess and hit it, but Brock Samson wrestled the location of it with a headlock.