Early travelers in Central Asia, such as William of Rubruk in the thirteenth and Odoric Pordenone in the fourteenth century reported "barbaric
costums" among Tibetans which involved sons cooking and eating the heads of their fathers and drinking to their memory out of skull cups.
Missionaries visiting Tibet in the seventeenth and eighteenth century were also puzzled by the widespread use of human skulls and bones for
religious purposes. When the Portuguese Jesuit d'Andrade asked about the significance of the skulls, he was told, in typically Buddhist fashion,
that they served as a reminder of life's impermanence and as a hindrance to sensual indulgence.
In 1888 Rockhill published his translation of the Tibetan manuscript on "The Use of Skulls in Lamaist Ceremonies". The reactions by scholars
such as Andree, Collin or Laufer were representative for the school of "Kulturmorphologie" as they tried to establish a historical connection
between the skull cults of different peoples in prehistory, antiquity and the Middle Ages. Their interpretation of the Tibetan use of skulls included
references to pre-Buddhist ancestor cults and head-hunting practices.
If we now examine reports in Sanskrit literature we find the earliest account in the Dasha-Kumara-Carita text of the sixth century which mentions
the use of skulls in Tantric rituals especially in connection with the cult of Shiva as Kapalabhrta or Mahakala, the Great Destroyer. Such usage
was also reported by the Chinese pilgrim Hiuen Tsang in the seventh century. In the twelfth century Ramanuja comments on the system of
Kalamukha as follows:
"Kalamukha teaches that the means of obtaining all desired results in this world as well as the next are constituted by certain practices - such as
using a skull as a drinking vessel, smearing oneself with the ashes of the dead body, eating the flesh of such a body..."
The very word "Kapala, translated a 'bowl', 'vessel', 'begging bowl' and also 'skull' implies already its specific ritualistic function. What the
Buddhist tradition concerns it is interesting to note, that in the Vinaya the use of a human skull as an almsbowl was explicitly forbidden. Only with
the spread of the Vajrayana system in India and Tibet did the humans skull gain its importance as a ritualistic implement.
As for the Tibetan sources, there is first to mention a text written in the twelfth century AD by the Sa skya scholar Grags pa rgyal mtshan entitled
"The Inner Offering Bowl in the Guhyamantrayana". It enumerates eight characteristics of a skull suitable for Tantric rituals, such as the "Feel of
it", its shape, colour, the number of sections, good and bad marks on the surface of the cranium ect.
Furthermore there is a text called "The Harmful and Richness bestowing Characteristics of Skulls", among the gter chos texts discovered by
Sangs rgyas gLing pa (1340-1396). This text includes instructions for a specific Kapala ritual.
In the fifteenth century Ratna gLing pa (1403-1478) discovered among the gYang gsang bLa med gTer chos another important ritual text called
"The Pith Instructions for the Siddhis of a Jewel Kapala". These two gTer ma texts are included in an dbu med written ancient manuscript which
contains as well a highly interesting story history on Kapala based on oral tradition.
During field studies in Darjeeling 1981/82 and in Tibet 1987 Loseries-Leick interviewed several traditional bone carvers, Lamas as well as sNgags
pa Yogis on the subject. These investigations proved that the oral tradition on skull cults is still alive in Tibet as well as in exile. Their survival is
most likely due to the fact that the relevant practices belong to a group of the highest Tantric teachings, the Anuttaratantras, and are therefore kept
secret. Loserier-Leick also verifies that the oral tradition largely tallies with the instructions given in the above mentioned written documents.