There is an old belief, buttressed by countless tales of apparitions,
that the devil always appears with a cloven foot as a sort
of distinguishing mark. It has been suggested that the Evil One,
having fallen lower than any man, is not permitted to take the
perfect human form but must have some sort of deformity (i.e.,
the cloven foot). It is also hypothesized that medieval Christian
imagery of the Devil merged with that of the pagan goat-footed
god Pan. The goat, of course, has a variety of occult associations,
including its inclusion in astrology in the sign of Capricorn
and the manifestation of incubi and succubi in the form
of a goat.
Cavendish, Richard. The Black Arts. New York G. P. Putnams
Russell, Jeffrey Burton. Witchcraft in the Middle Ages. Ithaca,
N.Y. Cornell University Press, 1972.