^w^ The rigid dorsal fin on the shark's back provides stability as the shark glides through the water.
^w^ The design of the `caudal` or tail fin varies greatly, depending on the lifestyle of the species. Some shark use their `lunate`, or "moon-like", tails for propulsion in slow cruising and high speed dashes. The Nurse Shark uses its long tail for broad side-to-side sweeps as it moves slowly through the water. The Blue Shark moves much like an eel, using its body and tail as it undulates at slow speeds.
^w^ All sharks have two pectoral fins to generate lift and prevent roll, pitch, and yaw. These fins, along with the tail or caudal fin, are also used for steering and braking. The spacing between the pectoral and the dorsal fins is critical to increased or decreased thrust -- necessary adaptations for a shark's predatory life style.
^w^ A pair of pelvic fins, closer to the tail, also assist in providing stability.
^w^ The head of the shark is flattened to prevent drag and facilitate lateral movement, while the higher middle section induces drag and acts as a fulcrum when the shark turns.
^w^ The buoyancy provided by low density oil in the liver and a lightweight cartilagenous skeleton help the shark, but most species cannot defy gravity and must maintain some movement to prevent sinking.
