164 



THE CIRCULATION OF THE BLOOD 



and partly covered by a membrane called the Eustachian valve. In the 

 posterior wall of the auricle is a slight depression called the fossa ovalis, 

 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 



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; 

 f, f, placed in the auriculo-ventricular groove, where a narrow portion of the adjacent 

 walls of the auricle and ventricle has been preserved; 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.) 



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



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



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 similunar or 



