A Vulcan spine and spinal cord.
The Spinal cord is an important part of a living being's nervous system that runs down the spine, and transmits the motor messages from the brain to the rest of the body. Spine
In 2367, Lieutenant Worf severely injured his spinal cord when a cargo container fell on his back, and was partially paralyzed. Doctor Toby Russell, a specialist, came aboard to offer assistance. She and Doctor Crusher tried to replace his spinal cord with a replicated one (made by Russell's invention, the genotron) however it failed, and Worf was pronounced dead. But his Klingon physiology provided him with a back-up spinal cord, and he survived the procedure. (TNG: "Ethics")