In tumblers there are either eleven, twelve, or thirteen sacral vertebrae.
"The Variation of Animals and Plants Under Domestication, Vol. I." by Charles Darwin
And in the consolidation of the sacral vertebrae of a bird it is also well exemplified.
"Essays: Scientific, Political, & Speculative, Vol. I" by Herbert Spencer
In birds the sacral vertebrae number from five to twenty-two.
"Dragons of the Air" by H. G. Seeley
It is possible to recognise cervical, dorsal, lumbar, sacral, and caudal vertebrae.
"The Cambridge Natural History, Vol X., Mammalia" by Frank Evers Beddard