the number of thoracic vertebrae can vary greatly; for example, most marsupials have 13, but koalas have only 11. 12 to 15 is common among mammals, with 18 to 20 in horses, tapirs, rhinoceroses, and elephants, and extremes in mammals are marked by certain sloths with 25 and cetaceans with 9. Additional images See also Costovertebral articulations Vertebral column Cervical vertebrae Lumbar vertebrae References External links Interactive tool to identify parts Photos at University of Utah SpineUniverse anatomical diagram Bones of the thorax Bones of the vertebral column