THE HEART 559 



The interior of the right auricle (Fig. 417) presents the following parts for 

 examination: 



Superior vena cava. 

 Inferior vena cava. 



j Coronary sinus. IT i ( Eustachian. 



Openings \ ^ . * rn , , .. Valves -s ~, 



roramina ihebesn. ( Loronary. 



Auriculoventricular. 

 .Anterior cardiac veins. 

 Fossa ovalis. 

 Annulus ovalis. 

 Tuberculum Loweri. 

 Musculi pectinati. 

 Crista terminalis. 



The superior vena cava (precava) returns the blood from the upper half of the 

 body, and opens into the upper and back part of the auricle, the direction of its 

 orifice being downward and forward. Its opening has no valves. 



The inferior vena cava (postcava), larger than the superior vena cava, returns 

 the blood from the lower half of the body, and opens into the lowest part of the 

 auricle near the septum, the direction of its orifice being upward and inward, 

 and guarded by a rudimentary valve, the Eustachian valve. The blood which 

 enters the auricle through the superior vena cava is directed downward and for- 

 ward, i. e., toward the auriculoventricular orifice, while that entering it through 

 the inferior vena cava is directed upward and backward toward the auricular 

 septum. This is the normal direction of the two currents in fetal life. 



The coronary sinus (sinus coronarius) opens into the auricle, between the inferior 

 vena cava and the auriculoventricular opening. It returns the blood from the 

 substance of the heart, and is protected by an incomplete semicircular fold of the 

 lining membrane of the auricle, the coronary valve, or valve of Thebesius. 



The foramina Thebesii (foramina venarum minimarum) are depressions in the 

 walls of the auricle; the majority of these are culs-de-sac, but about one third are 

 the orifices of minute veins (venae minimae cordis), which return the blood directly 

 from the muscle substance of the heart. 



The anterior cardiac veins open into the low r er fore part of the right auricle. 



The right auriculoventricular opening, or the tricuspid orifice (ostium venosum 

 dextrum), is the large oval aperture of communication between the right auricle 

 and the ventricle; it will be described with the right ventricle. 



The Eustachian valve (valvula veuae cavae inferioris [Eustachii\) is situated in 

 front of the orifice of the inferior vena cava. It is semilunar in form, its convex 

 margin being attached to the anterior margin of the inferior caval orifice; its con- 

 cave margin, which is free, terminates in two cornua, of which the left is continuous 

 with the anterior edge of the annulus ovalis, while the right is lost on the wall of 

 the auricle. The valve is formed by a duplicature of the lining membrane of the 

 auricle, containing a few muscle fibres. In the fetus this valve is of large size, 

 and tends to direct the blood from the inferior vena cava, through the foramen 

 ovale, into the left auricle. In the adult it is occasionally large, and may assist in 

 preventing the reflux of blood into the inferior vena cava; more commonly it is 

 small, and its free margin presents a cribriform or filamentous appearance; occa- 

 sionally it is altogether wanting. 



The coronary valve or valve of Thebesius (valvulae sinus coronarii [Thebesii]) 

 is a semicircular fold of the lining membrane of the auricle, protecting the orifice 

 of the coronary sinus. It prevents the regurgitation of blood into the sinus during 

 the contraction of the auricle. This valve is occasionally double. 



