The presence of a tail-like skin appendage located adjacent to the sacrum. [ https://orcid.org/0000-0002-0736-9199 http://www.ncbi.nlm.nih.gov/pubmed/18266249 http://www.ncbi.nlm.nih.gov/pubmed/23904413 http://www.ncbi.nlm.nih.gov/pubmed/18629881 ]
Synonyms: Human tail Sacral appendage Coccygeal tail