622 THE BLOOD-VASCULAR SYSTEM. 



The Coronary Sinus is that portion of the anterior or great cardiac vein which 

 is situated in the posterior part of the left auriculo-ventricular groove. It is about 

 an inch in length, presents a considerable dilatation, and is covered by the muscular 

 fibres of the left aui'icle. It receives the veins enumerated above, and an oblique 

 vein from the back part of the left auricle, the remnant of the obliterated left 

 Cuvierian duct of the foetus, described by Mr. Marshall. The great coronary 

 sinus terminates in the right auricle, between the inferior vena cava and the 

 auriculo-ventricular aperture, its orifice being guarded by a semilunar fold of the 

 lining membrane of the heart, the Thebesian valve. All the veins joining this 

 vessel, excepting the oblique vein above mentioned, are provided with valves. 



The Venae Thebesii (vence cordis minima') are numerous minute veins, which 

 return the blood directly from the muscular substance, without entering the venous 

 current. They open by minute orifices (foramina Thebesii) on the inner surface 

 of the right auricle. 



