The anatomy of the nasal passage of three specimens of the Boutu has been studied. The various diverticula appear to be aberrant from those described for other Platanistidae. The vestibular airsac system has developed into one enormous diverticulum. Except for a narrow region caudal to the blowhole, the total maxillary area caudal to the orbits is covered by this somewhat dome-shaped airsac system. The dorsal and rostral aspects of the vestibular system are strikingly symmetrical as are also the deeper parts of the nasal passage. The caudal parts of the nasofrontal diverticula are well developed, rostral parts are tubular and relatively small. Accessory air sacs are lacking and the premaxillary diverticula are broad, but their lumina rostral to the bony nares are nearly completely filled with dorsal swellings of the premaxillary bones when the former are deflated.