THE HEART 531 



The valve of the coronary sinus (valvula sinus coronarii [Thebesii]; Thebesian 

 valve) is a semicircular fold of the lining membrane of the atrium, at the orifice of 

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

 contraction of the atrium. This valve may be double or it may be cribriform. 



The fossa ovalis is an oval depression on the septal wall of the atrium, and corre- 

 sponds to the situation of the foramen ovale in the fetus. It is situated at the lower 

 part of the septum, above and to the left of the orifice of the inferior vena cava. 



The limbus fossae ovalis (annulus ovalis) is the prominent oval margin of the fossa 

 ovalis. It is most distinct above and at the sides of the fossa; below, it is deficient. 

 A small slit-like valvular opening is occasionally found, at the upper margin of 

 the fossa, leading upward beneath the limbus, into the left atrium ; it is the remains 

 of the fetal aperture between the two atria. 



The intervenous tubercle (tuberculum intervenosum; tubercle of Lower) is a small 

 projection on the posterior wall of the atrium, above the fossa ovalis. It is distinct 

 in the hearts of quadrupeds, but in man is scarcely visible. It was supposed by 

 Lower to direct the blood from the superior vena cava toward the atrioventricular 

 opening. 



Right Ventricle (wntriculus dexter). The right ventricle is triangular in form, 

 and extends from the right atrium to near the apex of the heart. Its antero- 

 superior surface is rounded and convex, and forms the larger part of the sterno- 

 costal surface of the heart. Its under surface is flattened, rests upon the dia- 

 phragm, and forms a small part of the diaphragmatic surface of the heart. Its 

 posterior wall is formed by the ventricular septum, which bulges into the right 

 ventricle, so that a transverse section of the cavity presents a semilunar outline. 

 Its upper and left angle forms a conical pouch, the conus arteriosus, from which 

 the pulmonary artery arises. A tendinous band, which may be named the tendon 

 of the conus arteriosus, extends upward from the right atrioventricular fibrous 

 ring and connects the posterior surface of the conus arteriosus to the aorta. The 

 wall of the right ventricle is thinner than that of the left, the proportion between 

 them being as 1 to 3; it is thickest at the base, and gradually becomes thinner 

 toward the apex. The cavity equals in size that of the left ventricle, and is 

 capable of containing about 85 c.c. 



Its interior (Fig. 493) presents the following parts for examination: 





n (Right atrioventricular. T7 , (Tricuspid. 



Openings Valves -s-r. , 



^ Pulmonary artery. (Pulmonary. 



Trabeculse carnese. Chordse tendinese. 



The right atrioventricular orifice is the large oval aperture of communication 

 between the right atrium and ventricle. Situated at the base of the ventricle, 

 it measures about 4 cm. in diameter and is surrounded by a fibrous ring, covered 

 by the lining membrane of the heart; it is considerably larger than the correspond- 

 ing aperture on the left side, being sufficient to admit the ends of four fingers 

 It is guarded by the tricuspid valve. 



The opening of the pulmonary artery is circular in form, and situated at the 

 summit of the conus arteriosus, close to the ventricular septum. It is placed above 

 and to the left of the atrioventricular opening, and is guarded by the pulmonary 

 semilunar valves. 



The tricuspid valve (valvula tricuspidalis) (Figs. 493, 495) consists of three some- 

 what triangular cusps or segments. The largest cusp is interposed between the 

 atrioventricular orifice and the conus arteriosus and is termed the anterior or infundib- 

 ular cusp. A second, the posterior or marginal cusp, is in relation to the right margin 

 of the ventricle, and a third, the medial or septal cusp, to the ventricular septum. 

 They are formed by duplicatures of the lining membrane of the heart, strengthened 





