 The "Journal Of The Indian Society Of Oriental Art" (volume 13) states 'in the ‘Taittiriya Aranyaka’, the earth is said to have been raised by a black boar with a hundred arms (‘"varahena krsnena satabahuna uddhrta"’).It is an easily understandable step to the making of the boar an incarnation of Visnu himself, a step which is finally taken in the epics and the Puranas'.This legend is also contained in the Mahanarayana Upanishad (p"rapāṭhaka" 10 of the Taittiriya Aranyaka)