This skull resides at the Franziskanerkirche in Salzburg, Austria, and is said to be that of Saint Eutyches. From the Curious Expeditions blog:
Though this skull is likely only a namesake, the original Eutyches was a Byzantine monk who was made an infamous heretic when he suggested that Christ was a sort of human-divine chimera. Though only a slight distinction from saying Christ was both fully human and fully divine, he was nonetheless cast out from the church and died in exile. […]
It rests on a gold embroidered pillow, surrounded by piles jewels and gold, but the most captivating detail of this magnificent skull are the brooch eyes. Settled into the eye sockets are two red jewels, mounted in flourishing silver settings. Finally it is adorned with a crown that reaches around the sides of it, like golden sideburns, meeting over the mouth of the skull in a grand jeweled mustache.