HEART RIGHT AURICLE. 693 



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 direc- 

 tion of the two currents in foetal life. 



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

 between' the two venae 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 vena 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 considerably 

 dilated. Its wall is partly muscular, and, at its junction with the great coronary 

 vein, is somewhat constricted, and furnished with a valve, consisting of two 

 unequal segments. 



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

 veins (vense cordis minimsi), 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, itt? 

 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 vena 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 vena cava ; more commonly, it is small, and its free 

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

 gether wanting. 



The coronary valve 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. 



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 auricu- 

 larum, 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 ; it is the remains 

 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. 



