THE RIGHT AURICLE. 4:>9 



coronary sinus. Other small apertures, named foramina of Tliebesius, 

 are scattered over this surface ; some lead only into depressions ; 

 but others are the mouths of veins of the substance of the heart 

 (smallest cardiac veins). vehis mallest 



The chief nurtures in the auricle are those of the two cavse, situation of 

 coronary sinus, and ventricle. The opening of the superior cava Cav8e > 

 is at the upper end of the auricle, and looks slightly forwards. 

 The inferior cava enters the lowest part of the cavity at the back, 

 close to the septum, and is directed inwards to the fossa ovalis. 

 The auriculo-ventricular opening is the largest of all, and is situate of auriculo- 

 at the lower and fore part of the cavity. Between this and the opeuii" llar 

 septum is placed the opening of the coronary sinus. of coronary 



All the large vessels, except the superior cava, have some kind of sinus - 

 valve. In front of the inferior cava is a thin fold of the lining Calves of 

 membrane of the cavity, the Eustachian valve, which is only a tures : 

 remnant of a much larger structure in the foatus. This fold is inferior 

 semilunar in form, with its convex margin attached to the anterior Eustachian 

 wall of the vein, and the other free in the cavity of the auricle. valve ; 

 The valve is wider than the vein opening ; and its surfaces are 

 directed forwards and backwards : it is often cribriform. The 

 aperture of the coronary sinus is covered by a thin fold of the one to coro- 

 lining membrane, which is prolonged internally on to the Eustachian nary S1 

 fold, and is known as the valve of Thebesius. The auriculo-ventri- 

 cular opening will be seen, in examining the right ventricle, to be and one to 

 provided with a tri-cuspid valve, which prevents the blood flowing ^"tricuiar 

 back into the auricle. opening. 



In the adult there is but one current of blood in the right auricle Course of 

 towards the ventricle. But in the foatus there are two streams in ^^1^. 

 the cavity ; one of pure, and the other of impure blood, which adult, 

 cross one another in early life. The placental or pure blood, and in tne 

 entering by the inferior cava, is directed by the Eustachian valve 

 into the left auricle, through the foramen ovale in the septum ; 

 while the current of systemic or impure blood, coming in by the 

 superior cava, flows downwards in front of the other to the right 

 ventricle. 



Dissection. To see the cavity of the right ventricle, the student To open 

 should raise outwards a V-shaped flap of the anterior wall of the "Jjltricle 

 ventricle, as in fig. 169, the blunted apex of the V being below the 

 root of the pulmonary artery, its upper border being parallel with, 

 but about half an inch below, the auriculo-ventricular groove and 

 the lower border being well to the right of the inter- ventricular 

 furrow, so as to avoid injury of the inter-ventricular septum. In the 

 examination of the cavity of the right ventricle, both the flap and 

 the apex of the heart should be raised with hooks or string, so 

 that the space may be looked into from below. 



The CAVITY OF THE RIGHT VENTRICLE (fig. 169) is triangular in Cavity of 

 form, with the base turned towards the auricle of the same side, "fntricle 

 On a cross section it would appear semilunar in shape, the septum 

 between the ventricles being convex towards the cavity. 



The apex of the cavity reaches the right border of the heart at Apex. 



