144 



THE CIRCULATION OF THE BLOOD 



which corresponds to an opening between the right and left auricles, exist- 

 ing in fetal life. In the appendix are closely set elevations of the muscular 

 tissue, covered with endocardium, and on the anterior wall of the auricle are 

 similar elevations arranged parallel to one another, called musculi pectinati. 



FIG. 135. The Right Auricle and Ventricle Opened and a Part of their Right and Anterior Walls 

 Removed so as to Show their Interior, i, Superior vena cava; 2, inferior vena cava; 2', hepatic 

 veins cut short; 3, right auricle; 3', placed in the fossa ovalis, below which is the Eustachian valve; 

 3", is placed close to the aperture of the coronary vein; t, t, placed in the auriculo- ventricular 

 groove, where a narrow portion of the adjacent walls of the auricle and ventricle has been pre- 

 served; 4, 4, cavity of the right ventricle, the upper figure is immediately below the semilunar 

 valves; 4', large columna carnea or musculus papillaris; 5, 5', 5", tricuspid valve; 6, placed in the 

 interior of the pulmonary artery, a part of the anterior wall of that vessel having been removed 

 and a narrow portion of it preserved at its commencement where the semilunar valves are attached ; 

 7, concavity of the aortic arch close to the cord of the ductus arteriosus; 8, ascending part or sinus 

 of the arch covered at its commencement by the auricular appendix and pulmonary artery; 9, 

 placed between the innominate and left carotid arteries; 10, appendix of the left auricle; n, n, 

 outside of the left ventricle the lower figure near the apex. (Allen Thomson.) 



The right ventricle forms the right margin of the heart. It takes no 

 part in the formation of the apex. On section its cavity is semilunar or 

 crescentic, figure 137. Into it are two openings, the auriculo-ventricular 

 orifice at the base, and the opening of the pulmonary artery, also at the base 

 but more to the left. The part of the ventricle leading to the pulmonary 

 artery is called the conus arteriosus or infundibulum; both orifices are guarded 

 by valves, the former called the tricuspid and the latter the semilunar. 



