There are (about) 206 bones in human body. The sacrum is a single bone that is the result of 5 bones fused together. Apparently that kicks @$$ on pigs and dogs!
Veterinary Dictionary: sacrum
The triangular-shaped bone between the lumbar and coccygeal vertebrae; formed usually by five fused vertebrae (four in pigs, three in dogs) that are wedged dorsally between the two hip bones.