part_of part of part of located in only in taxon develops from contributes to morphology of Vertebrata <vertebrates> Homo sapiens respiratory tube respiratory system thoracic cavity trachea http://upload.wikimedia.org/wikipedia/commons/9/9f/Illu_conducting_passages.svg http://upload.wikimedia.org/wikipedia/commons/c/c3/Illu_conducting_passages.jpg tracheal In birds, the trachea runs from the pharynx to the syrinx, from which the primary bronchi diverge. Swans have an unusually elongated trachea, part of which is coiled beneath the sternum; this may act as a resonator to amplify sound. In some birds, the cartilagenous 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 vertebrate to have lungs, but no trachea, is Polypterus, in which the lungs arise directly from the pharynx. tracheobronchial tree respiratory primordium