An anatomical investigation shows that between the branches of the pulmonary artery no anastomoses exist. It is, however, proved that under certain conditions connections between the larger branches of the artery may occur. This artificial connection is favored through peculiarities of terminal branching: wherever two parallel branches of the pulmonary artery are followed, it will be seen that the terminal branches lie alongside of each other without anastomosis. One can be convinced of that, and, further, that the capillaries of only one or two alveoli separate them. These unusually short capillaries between two arteries are those in which differences of pressure in one or the other artery produce wide connections. Küttner agrees so far with those observers who think that between the larger branches of the pulmonary artery no wide anastomoses exist already formed. In this sense the pulmonary artery can be designated a terminal artery; on the other side, however, it must not be forgotten that such connections can arise at any time, and the artery there loses the type of a so-called terminal artery.
He further remarks that the vascular-district supply of the pulmonary artery is not so limited as Cohnheim and Litten believe; that, more than that, some branches of it pass from one lobule to the adjoining one; that others are distributed in the subpleural and interlobular connective tissue and in the bronchial wall.
If the lung of an animal be injected from the pulmonary artery, there is produced a complete filling of the vessels of the bronchial wall and into the subepithelial layer—a fact the more interesting that a similar event can scarcely be produced by a filling of the bronchial artery.
Pulmonary Vein.—Only at the root of the lung do the bronchus, pulmonary artery, and pulmonary vein lie close to each other. In the continuance of the same the artery and the bronchus remain close by each other, but the vein pursues its own course. The branches of the same are, from the hilus to their capillary termination, situated in the interlobular connective-tissue paths. They form on the external margins of the lobules wide blutbuchten, in which the veins of the infundibula enter with short stems. The artery lies intralobular—the vein interlobular. The bronchial veins connect not only with branches of the azygos and superior cava, but also with those of the pulmonary vein.
Bronchial Vessels.—The variety of origin of the bronchial arteries is notable. Whatever their origin, they follow with their chief trunk the bronchus into the parenchyma of the lung, and give off insignificant lateral branches to the connective-tissue layers. There is still another kind of artery, which divides independently in the connective tissue of the lungs, without resting on the bronchial walls; they come from the oesophageal, mediastinal, and pericardial arteries, branch in the mediastinal pleura, appear with these at the hilus of the lung, and form partly an independent mesh of pleural arteries, and partly spread themselves in the interlobular connective tissue.
All the vessels of the serous membranes of the diaphragm can contribute in many ways blood to the hilus of the lung: the unusually fine-branched arteries appear in this way to be in condition to compensate for obstructions (or lesser). The bronchial arteries in comparison with the other vessels of the lungs give off sparingly lateral branches; among the most interesting are the branches which spring directly from the trunks of the bronchial artery, pass through the peribronchial connective tissue, appear at the adjoining infundibula, and lose themselves in capillary terminations.
The capillary districts of the bronchial arteries pass immediately into those of the pulmonary. It is a fact that besides the pulmonary artery the bronchial artery provides the infundibula and alveoli with blood. If the bronchial artery springing from the intercostal and internal mammary arteries be ligated or cut, leaving open the vessels of the mediastinal pleura, and the lung be injected from the abdominal aorta, a mere inspection will show a filling of the parenchyma of the lung; anastomoses between the pleural arteries and the intra-acinous trunks of the pulmonary arteries can be recognized. There is an anastomotic connection between the pleural branches of the pulmonary and bronchial arteries.
The bronchial, as also the pulmonary, artery can be filled by means of the fine arterial branches from the mediastinal pleura.
The principal branches of the bronchial arteries go to the bronchi; at the alveolar passage they here stop as such; their capillaries become continuous with those of the pulmonary artery. The greater part of the few collateral branches nourish the submucous peribronchial and perivascular connective tissue, the nerves, the lymphatic vessels; the smaller part enter the alveoli of other bronchial systems and become capillary.
The branches going to the lung with the mediastinal pleura spread themselves in the pleura and interlobular connective tissue, nourish the large subpleural and interlobular lymphatic vessels, but lose themselves in capillary distribution on the alveoli and infundibula.