When something is easy to determine and chazal says something that appears wrong,
What are you going to believe? Chazal, or the evidence in front of your eyes?
Rav Uren Riech said (empahsis mine):
Furthermore, the Rashba says (regarding terifos) that if someone comes up to you and tells you that he knows of a cow that lived more than 12 months with one of the simanei treifah that you should not believe him.
So, again, I ask you, who are you going to believe? Chazal when they say that man has 18 bones in his spine, or the “doctors” who say otherwise?
The Wolf