Skull symbolism is the attachment of symbolic meaning to the human skull. The most common symbolic use of the skull is as a representation of death and mortality, but such a reading varies with changing cultural contexts.
Humans can often recognize the buried fragments of an only partially revealed cranium even when other bones may look like shards of stone. The human brain has a specific region for recognizing faces, and is so attuned to finding them that it can see faces in a few dots and lines or punctuation marks; the human brain cannot separate the image of the human skull from the familiar human face. Because of this, both the death and the now past life of the skull are symbolized.
Moreover, a human skull with its large eye sockets displays a degree of neoteny, which humans often find visually appealing—yet a skull is also obviously dead. As such, human skulls often have a greater visual appeal than the other bones of the human skeleton, and can fascinate even as they repel. Our present society predominantly associates skulls with death and evil. However, to some ancient societies it is believed to have had the opposite association, where objects like crystal skulls represent “life”: the honoring of humanity in the flesh and the embodiment of consciousness.
When a skull was worn as a trophy on the belt of the Lombard king Alboin, it was a constant grim triumph over his old enemy, and he drank from it. In the same way a skull is a warning when it decorates the palisade of a city, or deteriorates on a pike at a Traitor’s Gate. The Skull Tower, with the embedded skulls of Serbian rebels, was built in 1809 on the highway near Niš, Serbia, as a stark political warning from the Ottoman government. In this case the skulls are the statement: that the current owner had the power to kill the former. “Drinking out of a skull the blood of slain (sacrificial) enemies is mentioned by Ammianus and Livy, and Solinus describes the Irish custom of bathing the face in the blood of the slain and drinking it.” The rafters of a traditional Jivaro medicine house in Peru, or in New Guinea. The temple of Kali is veneered with skulls, but the goddess Kali offers life through the welter of blood. The late medieval and Early Renaissance Northern and Italian painters place the skull where it lies at the foot of the Cross at Golgotha (Hebrew for the place of the skull). But for them it has become quite specifically the skull of Adam.
Text from: http://en.wikipedia.org/wiki/Skull_%28symbolism%29
