Apart from the caudal fin or caudal fin, the fin is not directly connected to the spine and is supported only by muscles. Fins can also be used for gliding and crawling, as seen in flying fish and frogfish. Bending the pectoral and caudal fins allows the fish to turn up, down, or sideways. The pectoral fins are also used as brakes, pushing them forward like flaps on an airplane wing. The position of the pair of fins, especially the pelvic fins, is constantly adjusted to prevent the fish from pitching or rolling. The pectoral muscles tend to lift, but this is counteracted by the downward thrust of the pelvis. The dorsal fin prevents the fish from rolling and helps with sharp turns and stops. In anglerfish, the front part of the dorsal fin is transformed into irisium and esca, the biological equivalents of fishing rods and lures. The bone that supports the dorsal fin is called the pterygoid process. There are two or three of them: "proximal" (axonost), "middle" (baseost), and "distal". In the case of rock-hard spinous fins, the distal pterygoid process is often fused with the central one or absent altogether. Boxfish, pufferfish, and sunfish use a combination of dorsal and anal fins for propulsion (four-toothed propulsion). A 2013 comparative study showed that adipose fins can develop in two different ways: the salmonid type, in which the adipose fin develops simultaneously from the larval fin folds and the other from the midline. It develops in the same direct way as the fins. The other is the mustard form pathway, in which the larval fin is reduced and the other median fin develops, followed by the late development of the adipose fin. They suggest that the adipose fin is not "just a remnant of larval fin folds", and argue for the existence of a characteristic developmental type that contradicts the view that the adipose fin has no function. Although homocercal fins usually appear symmetrical on the surface, the vertebrae actually extend a very short distance to the upper lobe of the fin. However, homocercal caudal fins can also appear asymmetrical. The fin is a small fin, generally behind the dorsal and anal fins (bitills have only a dorsal fin and no dorsal fin). In some fish, such as tuna and Pacific saury, rays are absent and cannot be retracted and are found on the last dorsal and/or between the anal and caudal fins. Teleosts have fin spines and rays called scaly hairs. They usually have a swim bladder that allows the fish to strike a neutral balance between sinking and swimming without using fins. However, many fish, especially lungfish, do not have a swim bladder. These fish are the only fish that retain the primitive lungs present in the common ancestor of the bony fishes from which swim bladders evolved. Teleosts have lids that allow them to breathe without using fins. Fish with lobe fins form a class of bony fish called sarcopterygii. They have fleshy, leafy, paired fins that are connected to the body by a series of bones. The fins of lobe-finned fish differ from the fins of all other fishes in that each is supported by a fleshy, leafy, scaly stem that extends from the body. The pectoral and pelvic fins have joints similar to the limbs of quadrupeds.