CORONARY VEINS. 435 



PULMONARY VEIN<. 



The pulmonary veins originate from the capillaries of the 

 corresponding arteries, in the walls of the air-cells and lesser 

 air-tubes. By repeated union they become larger, ultimately 

 converging to form from four to eight trunks, but usually four, 

 at the root of the lung, which enter the left auricle at various 

 points. They are destitute of valves, which permits easy reflux 

 of blood. These veins differ from others in the kind of blood 

 which they convey, the latter being arterial instead of venous. 



SYSTEMIC VEINS. 



The systemic veins commence in the capillaries, and, by 

 repeated union, form, in entering the right auricle, the cardiac or 

 coronary sinus, which opens directly into the cavity of the auricle ; 

 and two large trunks, the anterior and posterior venae cavae, which 

 terminate by two openings. There is a set of systemic veins 

 which neither go directly to the heart nor to the larger trunks ; 

 i.e., the veins of the cbylo-poietic viscera, which unite to form 

 the vena porta, terminating in the hepatic substance. 



CORONARY VEINS. 



The cardiac or coronary veins consist of one vena cordis magna 

 and numerous small venae cordis minimae. The greed coronary is 

 formed by two branches : one is lodged in the right ventricular 

 furrow, being a satellite of the descending branch of the right 

 coronary artery ; the other, a satellite of the left coronary artery, 

 passes up the left ventricular furrow to the origin of the pulmonary 

 artery, then backwards, turning round the base of the left ventricle, 

 finally uniting with the right branch near the termination of the 

 posterior cava; the common trunk, or coronary sinus, enters the 

 right auricle, receiving various branchlets from the ventricles and 

 auricles ; these have valves at their termination. The lesser 

 cardiac veins are numerous, coming chiefly from the walls of 

 the right side, penetrating it by the foramina Thebesii in the 

 right auricle. 



The bronchial veins, which return the venous blood from the 

 substance of the lungs, are satellites of, and disport themselves as 

 do the bronchial arteries. At the root of the lungs they form 

 one vein, which enters the great coronary just as it terminates 

 in the sinus, or , rarely enters the auricle separately. 



