three. In anglerfish, the anterior of the dorsal fin is modified into an illicium and esca, a biological equivalent to a fishing rod and lure. The two to three bones that support the dorsal fin are called the proximal, middle, and distal pterygiophores. In spinous fins, the distal pterygiophore is often fused to the middle or not present at all. Caudal/Tail fins: Also called the tail fins, caudal fins are attached to the end of the caudal peduncle and used for propulsion. The caudal peduncle is the narrow part of the fish's body. The hypural joint is the joint between the caudal fin and the last of the vertebrae. The hypural is often fan-shaped. The tail may be heterocercal, reversed heterocercal, protocercal, diphycercal, or homocercal. Heterocercal: vertebrae extend into the upper lobe of the tail, making it longer (as in sharks) Reversed heterocercal: vertebrae extend into the lower lobe of the tail, making it longer (as in the Anaspida) Protocercal: vertebrae extend to the tip of the tail; the tail is symmetrical but not expanded (as in cyclostomatans, the ancestral vertebrates and lancelets). Diphycercal: vertebrae extend to the tip of the tail; the tail is symmetrical and expanded (as in the bichir, lungfish, lamprey and coelacanth). Most Palaeozoic fishes had a diphycercal heterocercal tail. Homocercal: vertebrae extend a very short distance into the upper lobe of the tail; tail still appears superficially symmetric. Most fish have a homocercal tail, but it can be expressed in a variety of shapes. The tail fin can be rounded at the end, truncated (almost vertical edge, as in salmon), forked (ending in two prongs), emarginate (with a slight inward curve), or continuous (dorsal, caudal, and anal fins attached, as in eels). Anal fins: Located on the ventral surface behind the anus, this fin is used to stabilize the fish while swimming. Pectoral fins: Found in pairs on each side, usually just behind the operculum. Pectoral fins are homologous to the forelimbs of tetrapods, and aid walking in several fish species such as some anglerfish and the mudskipper. A peculiar function of pectoral fins, highly developed in some fish, is the creation of the dynamic lifting force that assists some fish such as sharks in maintaining depth and also enables the "flight" for flying fish. Certain rays of the pectoral fins may be adapted into finger-like projections, such as in sea robins and flying gurnards.