The avian respiratory system (the lung-air sac system) is exceptionally structurally complex and functionally efficient. The capacity of powered (active) flight in birds is largely attributed to these features. Although it has been investigated for a longtime, important questions on the bioengineering of the avian respiratory system still remain unclear and controversial. Among these are basis of the airflow dynamics in the lung, the structure and topographic arrangement of the airwayand the vascular systems and the shapes and sizes of the terminal respiratory units. Here, in attempt to resolve some of the issues, the lung of the domestic fowl, Gallus gallus variant domesticus, was investigated by three-dimensional (3D) serial section computer reconstruction. The bronchial-(airway) and the vascular systems were reconstructed and their morphologies thoroughly assessed to determine their morphologies and spatial relationships. Movies of the reconstructions were prepared and rotated to view the structures from different perspectives. Furthermore, the different parts of the pulmonary vasculature were extracted and reinserted into the reconstructions to determine whether anastomoses existed. The most important findings were: three main branches (= rami) of the pulmonary artery deliver venous (deoxygenated) blood to various parts of the lung; three main branches of the pulmonary vein drain arterial (oxygenated) blood from the lung; the third costal sulcus forms the approximate boundary between the cranialand the caudal blood supply-and drainage regions of the lung and; at least up to the level of the interparabronchial arteries and veins, no anastomoses (interconnections) were observed between the branches of the pulmonary artery and vein.