Evolution of the Dragon, by G. Elliot Smith, , at sacred-texts.com
The close association of the ram with the thunder-god is probably related with the fact that the sun-god Amon in Egypt was represented by the ram with a distinctive spiral horn. This spiral became a distinctive feature of the god of thunder throughout the Hellenic and Phnician worlds and in those parts of Africa which were affected by their influence or directly by Egypt.
An account of the widespread influence of the ram-headed god of thunder in the Soudan and West Africa has been given by Frobenius. 1
But the ram also became associated with Agni, the Indian fire-god, and the spiral as a head-appendage became the symbol of thunder throughout China and Japan, and from Asia spread to America where such deities as Tlaloc still retain this distinctive token of their origin from the Old World.
In Europe this association of the ram and its spiral horn played an even more obtrusive part.
The octopus as a surrogate of the Great Mother was primarily responsible for the development of the life-giving attributes of the spiral motif. But the close connexion of the Great Mother with the dragon and the thunder-weapon prepared the way for the special association of the spiral with thunder, which was confirmed when the ram with its spiral horn became the God of Thunder.
The relationship of the pig to the dragon is on the whole analogous to that of the cow and the stag, for it can play either a beneficent or a malevolent part. But the nature of the special circumstances which gave the pig a peculiar notoriety as an unclean animal are so intimately associated with the "Birth of Aphrodite" that I shall defer the discussion of them for my lecture on the history of the goddess.
134:1 Op. cit., vol. i., pp. 212-27.