Trachea act as a resonator to amplify sound. In some birds, the tracheal rings are complete, and may even be ossified. In amphibians, the trachea is normally extremely short, and leads directly into the lungs, without clear primary bronchi. A longer trachea is, however, found in some long-necked salamanders, and in caecilians. While there are irregular cartilagenous nodules on the amphibian trachea, these do not form the rings found in amniotes. The only vertebrates to have lungs, but no trachea, are the lungfish and the "Polypterus", in which the lungs arise directly from the pharynx. The word "trachea" is used to
Effect of spaceflight on the human body of motion sickness for the first three days of travel due to the conflict between what the body expects and what the body actually perceives. Over time however the brain adapts and although these illusions can still occur, most astronauts begin to see "down" as where the feet are. People returning to Earth after extended weightless periods have to readjust to the force of gravity and may have problems standing up, focusing their gaze, walking and turning. This is just an initial problem, as they recover these abilities quickly. NASA jokingly measures SAS using the "Garn scale", named for United