The two flukes are the fins which make up the dolphin's tail. They are flat and horizontal, and consist of tendons and fibrous tissue, but no bone. The flukes function as powerful paddles which are driven up and down (versus side to side in a fish) by the well-muscled tail stock, or "penducle". The long, powerful muscles of the penducle, some of which originate far forward on the back, need a strong attachment to the skeleton. The dolphin's vertebrae have specially adapted long spines which is used for just this purpose.
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