THE SYSTEMIC VEINS 283 



THE VEINS 



The veins, like the arteries, are of two great systems, the 

 pulmonary and the systemic. 



THE PULMONARY VEINS 



These are four large trunks, two on each side, which return 

 the blood from the lungs to the left auricle. On the right side 

 they pass behind the right auricle and superior vena cava; on 

 the left, in front of the descending aorta. The upper right vein 

 receives the branch from the middle lobe. 



THE SYSTEMIC VEINS 



The veins of the heart are : 



The great cardiac vein ascends in the anterior interventricular 

 groove from the apex of the heart to the left auriculo ventricular 

 groove; along this latter it runs to the posterior surface of the 

 heart, to end in the coronary sinus. At its termination it is 

 provided with a valve. 



Three or four posterior cardiac veins ascend on the left 

 ventricle to the sinus. 



The middle cardiac vein ascends in the posterior interven- 

 tricular groove to the sinus. 



The right (small) coronary vein in the right auriculoventric- 

 ular groove to the sinus. 



The coronary sinus, one inch long, is placed at the back part of 

 the auriculoventricular groove, on the left side, and opens into 

 the right auricle in front of the inferior vena cava. Besides the 

 foregoing veins, it receives the oblique vein of Marshall, which 

 drains the back of the left auricle. Its opening is guarded by the 

 Thebesian valve. 



The other cardiac veins are several small vessels from the 

 front of the right ventricle, the anterior cardiac veins, opening 

 directly into the auricle, and the venae Thebesii, in the muscular 

 substance, which open by minute orifices, the foramina Thebesii, 

 near the septum auricularum. 



