Plastered Human Skull from Jericho, c. 7000-6000 BC. Source
The use of human bones in art is an ancient practice. The inhabitants of the Neolithic Levant developed complex burial rituals and ideas about death. The deceased would often be buried directly under the foundations of their relatives' homes. Sometimes, they would be exhumed several years later and the skulls removed. The skull would be plastered, molded, and painted to resemble the departed individual. Skulls of one's ancestors were collected and used to decorate one's dwelling, offering a physical link to the past that may have been used to solidify one's genealogical right to their material possessions.
Painted lime plaster mask and skull, c. 100-170 AD. Source
The skull cults of the Ancient Near East created a sophisticated and widespread artistic tradition, but they were not at all unique in their practices. The Ancient Romans too held the skull in an esteemed position among one's bodily remains. This death mask from the 2nd century AD was created to be displayed on top of the owner's skull. This was very much like the practices of the Neolithic Levant, however the Roman artist appears to have been more virtuous in the realistic reconstruction of the details of the deceased's face.
A 16th century illustration of an Aztec tzompantli, from the Durán Codex. Source
Aztec tzompantli from the Templo Mayor at Tenochtitlan. Source
The Ancient Mesoamerican tzompantli, served the dual purpose of a memento mori for the members of the polity as well as for its enemies. These skull racks were constructed around megalithic temples with the remains of war captives and other sacrificial victims. The tzompantli served as a physical representation of the religious power of a deity and the military might of the polity's Lord. Ortíz de Montellano (1983) estimated that there were over 60,000 skulls on the Hueyi Tzompantli of Tenochtitlan, a truly terrifying monument to the power of the Aztec empire.
An ofrenda, Ciudad Universitaria, UNAM, Mexico. Source
The mortuary traditions of the Ancient Mesoamerican civilizations have survived to the modern day. In Mexico, the festival that would become Mexico's Día de los Muertos, The Day of the Dead, was celebrated by the Aztecs on the ninth month of their solar year. This was, and still is, a festival to remember one's ancestors and is a joyous, rather than remorseful celebration. The art surrounding the modern festival has many examples of skeletal imagery, such as this ofrenda, an offering of assorted goods placed around an ancestors grave during the festival.
Without Hope (1945) by Frida Kahlo.
The skeletal motif is found throughout contemporary Mesoamerican artwork. However, unlike the empires that once inhabited the region, modern artists shy from using real skulls as part of their work. This is most likely a result of the introduction of the hegemony of Judeo-Christian values. Also, skulls are probably a rarer possession in a time without sacrificial cults. You must wonder though, how powerful a mere image of a skull can be compared to art that is produced on actual skulls. Today, our mortuary prescriptions do not allow the disturbance of a body at rest, and it seems that the use of the human skeleton as a canvas is largely a dead art form. However, as shown by a post made a few weeks ago on an exhibit by Damien Hirst, the osseous canvas is still very much alive.