MRI examination of trachea and bronchi in the Ganges River dolphin (Platanista gangetica)

The MRI examination was carried out in a formalin-fixed specimen of the Ganges River dolphin (Platanista gangetica), one of the evolutionary primitive species of cetaceans. We could morphologically elucidate the tracheobronchial ramification in the intact whole body. We demonstrated from the MRI sections that the characteristic tracheal bronchus branches from the trachea at the cranial portion. These findings suggest the phylogenetic relationships between cetaceans and artiodactyls. The left bronchus is obviously larger in diameter than the right one. We suggest that the right bronchus has smaller capacity of gas exchange than the left one, because the dolphin possesses the tracheal bronchus in the right lung. The MRI method will be important in the non-invasive study of the anatomy in endangered animal carcass as Ganges River dolphin.