This is the mask. It is pre-Vedic. It is called vanaspati, a personification of the divine presence. It displays the illusion but hides the real.
It is also pre-Buddhist. Apparently there had been widespread worship to the devil or fire, which must have found its way to Tibet. In Tibet Bon-po, the worship of the demon was prevalent unitl the introduction of Buddhism. The mask here represents both the good and bad sides of a deity. Among the Tibetans the fire ritual represents purification.
The kirtimukha is a mystic mask that means the �Face of Glory� but it has generally grotesque aspects, ferocious and terrifying. It is diabolical and is meant to frighten the devil himself. The fierce deities are regarded as the guardians of the Buddha.