Out of his bowels? (I missed one earlier, sorry)

I can't believe I missed this one.  I just found while I was researching my next post.  Gen 15:4 says, “And, behold, the word of the LORD came unto him, saying, This shall not be thine heir; but he that shall come forth out of thine own bowels shall be thine heir.”  Out of his what?  Surely you can’t produce an heir out of there.  Many homosexual men have been trying that everyday with no such luck.  Maybe god, our creator doesn’t know anatomy?