208 



THE CIKCULATORY SYSTEM 



[cn. xviii. 



upon it of the septum ventriculorum, is crescentic (fig. 219); into it 

 are two openings, the auriculo-ventricular at the base and the opening 

 of the pulmonary artery also at the base, but more to the left ; both 

 orifices are guarded by valves, the former called tricuspid and the 



Fio. 217. The right auricle and ventricle opened, and a part of their right and anterior walls removed, 

 so as to show their interior. ^. 1, 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 ; + +, 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 ; 0, 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 th'e 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 ; 11, 11, the outside of the 

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



latter semilunar. In this ventricle are also the projections of the 

 muscular tissue called columnce carnece (described at length, p. 212). 



The left auricle is situated at the left and posterior part of the 

 base of the heart, and is best seen from behind. It is quadrilateral, 

 and receives on either side two pulmonary veins. The auricular 



