856 HUMAN ANATOMY. 



2. The Posterior Cardiac Vein. — The posterior cardiac vein (v. posterior 

 ventriculi sinistrij ascends along the posterior surface of the left ventricle, lying about 

 midway between the left border of the heart and the posterior interventricular groove 

 and receiving collateral branches from the walls of the ventricle. It opens above 

 into the coronary sinus near the point of entrance of the great coronary vein and 

 occasionally unites with that vessel. 



3. The Middle Cardiac Vein. — The middle cardiac vein (v. cordis media) 

 (Fig. 750) occupies the posterior interventricular groove, accompanying the right 

 coronary artery. It arises in the vicinity of the apex of the heart and ascends, 

 recei\ang collateral branches from the posterior surfaces of both ventricles, to open 

 into the coronary sinus near its termination. This, next to the great coronary vein, is 

 the largest vein of the heart, and occasionally opens independently into the right 

 auricle close to the entrance of the coronary sinus. 



4. The Right Coronary Vein. — The small cardiac or right coronary vein 

 (v. cordis pan'aj (Fig. 750) occupies, when present, the right half of the posterior 

 auriculo-ventricular groove and opens into the coronary sinus just before its termi- 

 nation. Occasionally it opens into the middle cardiac vein, or directly into the 

 right auricle, and is not infrequently lacking as a distinct vessel, the tributaries 

 which empty into it from the posterior surface of the right auricle and the upper 

 part of the posterior surface of the right ventricle then opening directly into the 

 auricle. One of the largest and most constant of these tributaries ascends along 

 the right border of the right ventricle and is termed the right marginal vein or 

 vein of Galen. 



5. The Oblique Vein of the Left Auricle. — The oblique vein of the left 

 auricle (v. obliqua atrii sinistri), also known as Marshair s vein, is a small vein of 

 variable development which descends obliquely over the posterior surface of the left 

 auricle and opens below into the coronary sinus. Above, it is continuous with a 

 fibrous cord contained within the vestigial fold of the pericardium (page 716), the 

 cord and vein together representing the lower part of an original left superior vena 

 cava. The degree of development of the vein varies greatly, and occasionally the 

 fibrous cord retains its original lumen, so that a more or less developed left superior 

 vena cava is really present. This anomaly may, however, be more conveniently 

 considered in connection with those of the superior caval system of veins (page 859). 



In addition to these principal veins of the heart there is a varying number of 

 others which open directly into the right auricle and are . situated upon the anterior 

 surface of the right ventricle, whence they have been termed the anterior cardiac 

 veins (vv. cordis anteriores ). They are all comparatively short vessels and usually 

 accompany descending branches of the right coronary artery. Owing to the fre- 

 quency with which it opens directly into the auricle, the vein of Galen is usually 

 regarded as one of this group of veins. 



Finally, the Thebesian veins (vv. cordis minimae) form part of the cardiac 

 venous system. These are minute veins, imbedded in the substance of the heart 

 walls, and communicating with the heart cavities by means of the Thebesian foramina 

 (page 716), which occur most abundantly upon the walls of the right auricle, though 

 also upon those of the left auricle, and, less abundantly, upon those of the ventricles. 

 At their other ends these veins communicate in the heart's substance with the radicles 

 of the other cardiac veins, and, in cases of stenosis of the coronary arteries, may 

 consequently contribute to some extent to the nutrition of the heart musculature, 

 carrying blood to it directlv from the heart cavities. 



Valves of the Cardiac Veins. — The Thebesian valve, which guards the right 

 auricle, may be considered as the ostial valve of that vessel, which throughout its 

 course is destitute of valves. So, too, throughout the extent of the cardiac veins 

 valves are entirely lacking, but certain of those which open into the coronary sinus 

 are provided with ostial valves. That of the great coronary vein is the valve of 

 Vieussens, and others are usually present at the mouths of the middle vein and the 

 posterior vein of the left ventricle, and less constantly at the mouths of the marginal 

 and the small coronary veins. These valves may be either single or paired and are 

 frequently insufiflcient. No valves are present either throughout the course or at the 

 orifice of the oblique vein of the left auricle. 



