472 VALVES OPENINGS. 



these two vessels is such, that a stream forced through the superior 

 cava would be directed towards the auriculo-ventricular opening. 

 In like manner, a stream rushing upwards by the inferior cava 

 would force its current against the septum auriculorum ; this is the 

 proper direction of the two currents during foetal life. 



The Coronary vein returns the venous blood from the substance 

 of the heart ; it opens into the auricle between the inferior cava and 

 the auriculo-ventricular opening, under cover of the coronary valve. 



The Foramina Thebesii* are minute pore-like openings, by which 

 the venous blood exhales directly from the muscular structure of the 

 heart into the auricle, without entering the venous current. These 

 openings are also found in the left auricle, and in the right and left 

 ventricles. 



The Auricula-ventricular opening is the large opening of com- 

 munication between the auricle and ventricle. 



The Eustachian^ valve is a part of the apparatus of fetal cir- 

 culation, and serves to direct the placental blood from the inferior 

 cava, through the foramen ovale into the left auricle. In the adult 

 it is a mere vestige and imperfect, though sometimes it remains of 

 large size. It is formed by a fold of the lining membrane of the 

 auricle, containing some muscular fibres, is situated between the 

 opening of the inferior cava and the auriculo-ventricular opening, 

 and is generally connected with the coronary valve. 



The Coronary valve is a semilunar fold of the lining membrane, 

 stretching across the mouth of the coronary vein, and preventing 

 the reflux of the blood in the vein during the contraction of the 

 auricle. 



The Jlnnulis ovalis is situated on the septum auriculorum, oppo- 

 site the termination of the inferior cava. It is the rounded margin 

 of the septum, which occupies the place of the foramen ovale of 

 the fetus. 



The Fossa ovalis is an oval depression corresponding with the 

 foramen ovale in the fetus. This opening is closed at birth by a 

 thin valvular layer, which is continuous with the left margin of the 

 annulis and is frequently imperfect at its upper part. The depres- 

 sion or fossa in the right auricle results from this arrangement. 

 There is no fossa ovalis in the left auricle. 



The Tuberculem LowerQ is the portion of auricle intervening be- 

 tween the openings of the superior and inferior cava. Being thicker 

 than the walls of the veins it forms a projection, which was supposed 

 by Lower to direct the blood from the superior cava into the auri- 

 culo-ventricular opening. 



* Adam Christian Thebesius. His discovery of the openings now known by his 

 name, is contained in his " Dissertatio Medica de Circulo Sanguinis in Corde," 1 708- 



t Bartholomew Eustachius, born at San Severino, in Naples, was Professor of Medi- 

 cine in Rome, where he died in 1570. He was one of the founders of modern anatomy, 

 and the first who illustrated his works with good engravings on copper. 



t Richard Lower, M.D. " Tractatus de Corde ; item de Motu et Colore Sanguinis," 

 1669. His dissections were made upon quadrupeds, and his observations relate rather 

 to animals than to man. 



