The skull cup is fashioned from the oval upper section of a human cranium, and serves as an offering, eating or liabation bowl for a large number of Vajrayana deities.  It is held in the left hand of yoginis, siddhas, dakinis, yidams and protective deities.  It contains such substances as: divine nectar (Skt. amrita), vital nectar (semen), alcohol, ritual cakes or tormas, fresh blood, marrow, intestines, fat, as well as the brains, heart and lungs of demonic enemies who are personified as maras ans rudras.  The qualities attributed to the differing sources of human bone utilized for skull-cups follows a similar sequence to the thighbone trumpet, with the skull of a Brahmin, r a victim of murder or execution being considered the most effective medium for wrathful practices.  The skull of a child who died during the onset of puberty also has great potency as does the "misbegotten skull" (Tib. nal-thod) of a 7-8 year old child born from an incestuous union.  A skull full f "charm blood" (Tib. thun-khrag) is a specific attribute of the wrathful goddess Shri Devi in her form as the "Glorious Army-averting Queen".

The skullcup is usually held in the left "wisdom" hand  and held in front of the deity's heart where it may be paired with such right hand 'method' implements such as the vajra or curved knife.  Many wrathful protective and yidam deities hold a curved knife above a skull cup in front of their hearts symbolizing the union of their method and wisdom.  The curved knife serves as the "method" weapon that severs the life and vital organs of demonic enemies and the skull cup is the "wisdom" vessel in which the blood and organs are collected as the deity's life source.

The tantric staff (Skt. khatvanga), hand drum (Skt. dhamaru) and skull cup (Skt. kapala) are the three main attributes of the the Hindu kapalika yoginis and these three symbols were absorbed into the tantric Buddhist siddha lineages as representations of the body, speech and mind of the deity.  The khatvanga represents the body or consort, the damaru represents speech, and the kapala represents the mind.