642 ANGIOLOGY 



THE PULMONARY VEINS (VEN-ffi PULMONALES). 



The pulmonary veins return the arterialized blood from the lungs to the left 

 atrium of the heart. They are four in number, two from each lung, and are desti- 

 tute of valves. The commence in a capillary net-work upon the walls of the air sacs, 

 w 7 here they are continuous with the capillary ramifications of the pulmonary artery, 

 and, joining together, form one vessel for each lobule. These vessels uniting 

 successively, form a single trunk for each lobe, three for the right, and two fo'r 

 the left lung. The vein from the middle lobe of the right lung generally unites 

 with that from the upper lobe, so that ultimately two trunks from each lung are 

 formed; they perforate the fibrous layer of the pericardium and open separately 

 into the upper and back part of the left atrium. Occasionally the three veins 

 on the right side remain separate. Not infrequently the two left pulmonary 

 veins end by a common opening. 



At the root of the lung, the superior pulmonary vein lies in front of and a little 

 below the pulmonary artery; the inferior is situated at the lowest part of the hilus 

 of the lung and on a plane posterior to the upper vein. Behind the pulmonary 

 artery is the bronchus. 



Within the pericardium, their anterior surfaces are invested by the serous layer 

 of this membrane. 



The right pulmonary veins pass behind the right atrium and superior vena cava; 

 the left in front of the descending thoracic aorta. 



THE SYSTEMIC VEINS. 



The systemic veins may be arranged into three groups : (1) The veins of the heart. 

 (2) The veins of the upper extremities, head, neck, and thorax, which end in the 

 superior vena cava. (3) The veins of the lower extremities, abdomen, and pelvis, 

 which end in the inferior vena cava. 



THE VEINS OF THE HEART (VV. Cordis) (Fig. 556). 



Coronary Sinus (sinus coronarius). Most of the veins of the heart open into 

 the coronary sinus. This is a wide venous channel about 2.25 cm. in length 

 situated in the posterior part of the coronary sulcus, and covered by muscular 

 fibers from the left atrium. It ends in the right atrium between the opening of 

 the inferior vena cava and the atrioventricular aperture, its orifice being guarded 

 by a semilunar valve, the valve of the coronary sinus (valve of Thebesius) . 



Tributaries. Its tributaries are the great, small, and middle cardiac veins, the 

 posterior vein of the left ventricle, and the oblique vein of the left atrium, all of 

 which, except the last, are provided with valves at their orifices. 



1. The Great Cardiac Vein (v. cordis magna; left coronary vein) begins at the apex 

 of the heart and ascends along the anterior longitudinal sulcus to the base of the 

 ventricles. It then curves to the left in the coronary sulcus, and reaching the 

 back of the heart, opens into the left extremity of the coronary sinus. It receives 

 tributaries from the left atrium and from both ventricles: one, the left marginal 

 vein, is of considerable size, and ascends along the left margin of the heart. 



2. The Small Cardiac Vein (v. cordis parva; right coronary vein) runs in the coronary 

 sulcus between the right atrium and ventricle, and opens into the right extremity 

 of the coronary sinus. It receives blood from the back of the right atrium and 

 ventricle; the right marginal vein ascends along the right margin of the heart and 

 ioins it in the coronary sulcus, or opens directly into the right atrium. 



