The head of the three-toed sloth swivels 270 degrees thanks to three extra cervical vertebrae.
1=Three toed sloth at the Dallas World Aquarium
''Bradypus variegatus'' of "Museu de Zoologia" of Barcelona
"Because the three-toed sloth has three extra cervical vertebrae than other mammals, including its close relative the two-toed sloth, it is able to turn its head 270 degrees, or three-quarters the way around." (Young 1999)