HEART RIGHT AURICLE. 759 



Openings. The superior vena cava returns the blood from the upper half of 

 the body, and opens into the upper and front part of the auricle, the direction 

 of its orifice being downwards and forwards. 



The inferior vena cava, larger than the superior, 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 upwards and inwards. The direction 

 of a current of blood through the superior vena cava would consequently be 

 towards the auriculo-ventricular orifice ; whilst the direction of the blood 

 through the inferior cava would be towards the auricular septum. This is the 

 normal direction of the two currents in foetal life. 



The tuberculum Loweri is a small projection on the right wall of the auricle, 

 between the two cavae. This is most distinct in the hearts of quadrupeds ; in 

 man, it is scarcely visible. It was supposed by Lower to direct the blood from 

 the superior cava towards the auriculo-ventricular opening. 



The coronary sinus opens into the auricle, between the inferior vena cava and 

 the auriculo-ventricular opening. It returns the blood from the substance of 

 the heart, and is protected by a semicircular fold of the lining membrane of 

 the auricle, the coronary valve. The sinus, before entering the auricle, is con- 

 siderably dilated. Its wall is partly muscular, and,' at its junction with the 

 great coronary vein, is somewhat constricted, and furnished with a valve, con- 

 sisting of two unequal segments. 



The foramina Thebesii are numerous minute apertures, the mouths of small 

 veins (vense cordis minim ae), which open on various parts of the inner surface of 

 the auricle. They return the blood directly from the muscular substance of the 

 heart. Some of these foramina are minute depressions in the walls of the heart, 

 presenting a closed extremity. 



The auriculo-ventricular opening is the large oval aperture of communication 

 between the auricle and ventricle, to be presently described. 



Valves. The Eustachian valve is situated between the anterior margin of the 

 inferior cava and the auriculo-ventricular orifice. It is semilunar in form, its 

 convex margin being attached to the wall of the vein ; its concave margin, 

 which is free, terminating in two cornua, of which the left is attached to the 

 anterior edge of the annulus ovalis ; the right being lost on the wall of the 

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

 auricle, containing a few muscular fibres. 



In the foetus, this valve is of large 'size, and serves to direct the blood from 

 the inferior cava, through the foramen ovale, into the left auricle. 



In the adult, it is occasionally persistent, and may assist in preventing the 

 reflux of blood into the inferior cava ; more commonly, it is small, and its free 

 margin presents a cribriform, or filamentous appearance ; occasionally, it is 

 altogether \vanting. 



The coronary valve is a semicircular fold of the lining membrane of the auri- 

 cle, 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. 



The fossa ovalis is an oval depression, corresponding to the situation of the 

 foramen ovale in the foetus. It is situated at the lower part of the septum auri- 

 cularum, above the orifice of the inferior vena cava. 



The annulus ovalis is the prominent oval margin of the foramen ovale. It is 

 most distinct above, and at the sides; below it is deficient. A small slit-like 

 valvular opening is occasionally found, at the upper margin of the fossa ovalis, 

 which leads upwards, beneath the annulus, into the left auricle, and is the re- 

 mains of the aperture between the two auricles in the foetus. 



The musculi pectinati are small, prominent muscular columns, which run across 

 the inner surface of the appendix auriculae and adjoining portion of the wall of 

 the sinus. They have received the name pectinati from the fancied resemblance 

 they bear to the teeth of a comb. 



