caudal vs sacrum

caudal

noun
  • A caudal vertebra. 

adj
  • Toward the tail end (hind end) of the body; in bipeds such as humans, this direction corresponds to inferior. 

  • Pertaining to the tail or posterior or hind part of a body. 

sacrum

noun
  • A large triangular bone at the base of the spine, located between the two ilia (wings of the pelvis) and formed from vertebrae that fuse in adulthood. 

How often have the words caudal and sacrum occurred in a corpus of books? (source: Google Ngram Viewer )