Spine

The spine was part of the musculoskeletal structure of humanoid species. After House murdered the Time Lord known as the Corsair, his spine was given to Uncle, one of House's patchwork slaves. (TV: The Doctor's Wife)

Having been tricked by the Eleventh Doctor into disarming his forces, leaving them defenceless as an army of Silurian warriors and Judoon troopers arrived on Demons Run, as well the communications array of the base destroyed so a distress call could not be sent, Colonel Manton was advised by Sontaran nurse Commander Strax not to slump as it was bad for his spine. (TV: A Good Man Goes to War)

Inhabitants of the planet Cristic have two spines. (AUDIO: Vesuvius Falling)