Pavlov, V.: Morphological Adaptation of Dorsal Fin of Harbour Porpoise (Phocoena phocoena) to Swimming and Thermal Regulation Function

Dorsal fin is an example of particular specialization of an organ having combined function of stabilization of motion and heat regulation. The shape of the fin was evaluated by the set of wing and foil parameters: angle of leading edge sweep, leading edge radius, maximum thickness of the foil, position of maximum thickness from the leading edge. The distribution of thickness of epidermis, papillary and sub-papillary layers of dermis, ligamentous layer of fin as well as dermal ridges direction, 3D structure of dermal-epidermal joint, central core structure and characteristic features of the blood system of dorsal fin had been studied. It was found that morphology parameters of dorsal fin depend on wing and foil parameters. Since the skin structure is the base of the skin mechanical properties, the founded regularity can be considered as an indirect evidence of correspondence of passive mechanical properties of the surface to the fin flow. The central core structure assigns smooth decrease of the rigidity of dorsal fin in chordwise and spanwise directions. Ligamentous layer being elastic and almost not extensible braid of fin prevents from excessive bending in these directions. The characteristic feature of dorsal fin blood system consists in existence of combined vessels in the central core, where the braid of veins surrounds arteries as well as the system of big veins beneath the ligamentous layer. Such characteristic provides an effective heat exchange between venous and artery blood as well as transfer of the heat redundancy into the environment. Dorsal fin design is the compromise between wing performance and requirements of thermal regulation.