RIGHT AURICLE OF HEART. 317 



and top of the auricle, and its direction is forwards. The inferior cava (i) 

 enters the back part of the cavity near the septum, and is directed back- 

 wards to the fossa ovalis (d). The auriculo-ventricular opening (e) is the 

 largest of all, and is situate at the lowest part of the cavity. Between this 

 and the septum is placed the opening of the coronary sinus (e) which is 

 about as large as a turkey-quill. 



All the large vessels, except the superior cava, have some kind of valve. 

 In front of the inferior cava is a thin fold of the lining membrane of the 

 cavity, the Eustachian valve, which is only a remnant of a much larger 

 structure in the foetus. This valve in its perfect state is semilunar in form, 

 with its convex margin attached to the anterior wall of the vein, and the 

 other free in the cavity of the auricle. It is wider than the vein opening, 

 and its surfaces are directed forward and backwards : its free margin is 

 often reticular. The aperture of the coronary sinus is closed by a thin 

 fold of the lining membrane valve of Thebesius. The auriculo-ventricu- 

 lar opening will be seen, in examining the right ventricle, to be provided 

 with valves, which prevent blood running back into the auricular cavity. 



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

 the ventricle. But in the foetus there are two streams in the cavity : one 

 of pure, and the other of impure blood, which cross one another in early 

 life, but become more commingled as birth approaches. The placental or 

 pure blood entering by the inferior cava, is directed by the Eustachian 

 valve chiefly into the left auricle, through the foramen ovale in the sep- 

 tum ; whilst 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 should 

 pierce it with the scalpel below the opening from the auricle, and cut out 

 interiorly near the apex of the heart without injuring the septum ventricu- 

 lorum. A flap is thus formed, like the letter V, of the anterior part of the 

 ventricle. 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. 100) is triangular in form, 

 and has the base turned upwards to the auricle of the same side. On a 

 cross section the cavity would appear semilunar in shape, with the sep- 

 tum between the ventricles convex towards the cavity. 



The apex of the cavity reaches the right border of the heart at a short 

 distance from the tip. The base of the ventricle is sloped, and is perfo- 

 rated by two apertures ; one of these, on the right, leading into the auri- 

 cle, is the right auriculo-ventricular opening (c) ; the other on the left, 

 and much higher, is the mouth of the pulmonary artery (g). The part of 

 the cavity communicating with the pulmonary artery is funnel-shaped, 

 and is named infundibulum or conus arteriosus. 



The anterior wall, or the loose part of the ventricle, is comparatively 

 thin, and forms most of the anterior surface of the ventricular portion of 

 the heart. The posterior wall corresponds with the septum between the 

 ventricles, and is much thicker. 



Over the greater part of the cavity the surface is irregular, and is marked 

 by projecting fleshy bands of muscular fibres, the columnce carnece ; but 

 near the aperture of the pulmonary artery the wall becomes smooth. The 

 fleshy columns are of various sizes, and of three different kinds. Some 

 form merely a prominence in the ventricle, as on the septum. Others are 

 attached at each end, but free in the middle (trabeculse carneae). And a 



