Luzivaldo Castro dos Santos Júnior; Miriam Marmontel; Francisco Glauco de Araújo Santos; Rose Eli Grassi Rici; Maria Angélica Miglino & Yuri Karaccas de Carvalho

This study aimed to characterize the structures of the posterior respiratory system of two species of river dolphins: Inia geoffrensis and Sotalia fluviatilis. The respiratory tract of both species was evaluated using macro and microscopic techniques. Four macroscopic anatomical structures were identified: Trachea, main bronchus, tracheal bronchus and lung. The presence of the exuberant tracheal bronchus suggested ease of gas exchanges. Histological analysis revealed the presence of alveolar ducts and myoelastic sphincter in these Amazonian cetaceans. The posterior respiratory portion of the Amazonian dolphins presents similarity with other odontocetes and the knowledge of this structure can also help contribute to the understanding of the physiology of diving and how these species are adapted to their habitat.

KEY WORDS: Amazon river dolphin; Tucuxi; Anatomy.