Humpback Whale Pectoral Fin. Humpback whale pectoral fins, also called flippers, can grow up to 5 meters (16 feet) long, making them proportionally the largest among cetaceans, sometimes nearly one-third of the whale’s total body length. Internally, these fins contain bones analogous to a human arm, including shoulder blades, humerus, radius, and finger-like phalanges, adapted over millions of years for aquatic life. If you look back at the Humpback Skelton images in day 14 of this gallery, you can see these "finger-like phalanges".

The leading edges of the fins have scalloped bumps called tubercles, which reduce drag and increase lift, enhancing maneuverability