R. Jeremiah b. Eleazar said: The first man had two full faces, for it is said in Scripture: Thou hast shaped me behind and before. (PS. 139:5)
The Hebrew word tzartani , usually translated as “hemmed me in (before and after)” is here connected to tzurah (shape). This, along with the statement:
And the Lord God builded the side (tzaylah), etc. (Gen. 2:22)
This creates a midrashic idea that G-d constructed Adam differently in the front than in behind.
What could that difference be? There are two schools of thought: “a full face” and “a tail.”
A “full face” means that Adam and Eve were created from the beginning as one entity – male and female back to back. “A tail” means that Adam was created originally as a tailed being, and that Eve was built up from that tail.
G-d either split the doubled human or split off the tail. The textual proofs and challenges for both are explored. But in either case, it is a far different story that Adam’s Rib!
And this is the strength of Jewish biblical interpretation – such views only strengthen not challenge the text.