The skull as a symbol is merely 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. The human brain cannot separate the image of the human skull from the familiar human face. Because of this, both the death of, and the now past life of the skull are symbolized.

The use of the skull, for whatever reasons in the arts has a rich and varied tradition. Since the artist could not possible take these images as true self-portraits, the artist freely uses artistic license to interpolate memento mori into the work. Memento mori is a Latin phrase which means very simply "Remember you will die". It names a genre of artistic creations that vary widely from one another, but which all share the same purpose: to remind people of their own mortality and the punishment they will receive if they transgress the rules of their religion.

Also, true to the genre, artists created symbolic still life paintings that were later used in portraiture as well to express vanitas, which is a Latin phrase that means "emptiness" and loosely translated corresponds to the meaninglessness of earthly life and the transient nature of vanity. Thanks for visiting and please come back often!