Usage examples for backbone:

• But she was " pluck" to the backbone "A Terrible Secret" – May Agnes Fleming

• Won- tolla said not a word, only his jaws were closing and closing on the backbone as his life ebbed. "The Second Jungle Book" – Rudyard Kipling

• Old Sergeant Gamelyn came of an ancestry which, somebody or other of distinction once said- and very truly- is the backbone of the British Army. "War and the Weird" – Forbes Phillips R. Thurston Hopkins