Morphology of the pectoral girdle in the Amazon dolphin Inia geoffrensis with special reference to the Shoulder joint and the movements of the flippers

Studied the Shoulder girdle in the Amazon dolphin Inia geoffrensis in comparison with that of Tursiops truncatus and Phocoenaphocoena . In contrast to marine dolphins, in Inia the sternum takes part in the formation of the Shoulder joint, the latter coming near to an enarthrosis. The well developed appropriate muscles have single, rather dispersed insertions into the humerus and render possible manifold movements of the flipper in all directions. By this Inia geoffrensis attains a particularly high manoeuvrability advantageous for life in the shallow waters of the Amazon river System.