Reference for Berakhot 121:7

רב ושמואל חד אמר פרצוף וחד אמר זנב

One declared that it was a face [from which Eve was made] ; the other declared that it was a tail. It is right according to him who says that it was a face; that is what is written, "Behind and before hast Thou formed me." But according to him who said it was a tail, what means "Behind and before hast Thou formed me"? It is [to be explained]

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