The functional anatomy of the bronchial circulation of the domestic fowl.

The bronchial circulation was studied in 25 adult domestic fowls. The right and left bronchial arteries originated caudal to the syrinx from a bronchoesophageal artery which is a branch of the right common carotid artery. Each bronchial artery ramified on the wall of the extrapulmonary part of the corresponding primary bronchus and finally anastomosed directly with a branch of the pulmonary artery at the hilus of the lung. Thr bronchial artery did not accompany the intrapulmonary part of the primary bronchus. The branches of each bronchial artery formed an anastomosing network on the wall of the extrapulmonary part of the primary bronchus. The calibre of the bronchial artery at its anastomosis with the branch of the pulmonary artery was greater than at its origin from the bronchoesophageal artery. Intravenous injections of Lycopodium spores indicated that the blood flows from the pulmonary artery into the bronchial artery. Small bronchial veins drained the extrapulmonary part of the primary bronchus into the pulmonary vein and the oesophageal veins. The intrapulmonary part of the primary bronchus was supplied by branches of the pulmonary artery and drained by tributaries of the pulmonary vein. The blood supply to the primary bronchus could constitute a shunt capable of passing blood from the pulmonary artery into the pulmonary vein without going through the exchange tissue. The parabronchial (atrial) muscles received a blood supply directly from the exchange tissue via septal venules which formed a network underneath the muscle bundles, without actually penetrating between the muscle cells. These venules drained into atrial veins which were tributaries of the pulmonary vein. The atrial muscles probably also received oxygen by direct diffusion from the parabronchial lumen. The pleura was supplied by the oesophageal branches of the bronchoesophageal artery, and by small twigs from the internal thoracic and intercostal arteries.