210 



THE CIRCULATORY SYSTEM 



[CH. XIX. 



its cavity, in consequence of the encroachment upon it of the septum 

 ventriculorum, is crescentic (fig. 193); it has two openings, one 

 communicating with the right auricle, and the other with the 

 pulmonary artery ; both orifices are guarded by valves, the former 

 called tricuspid and the latter semilunar. 



FIG. 191. 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 ; 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 ; 11, 11, the outside of the 

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



The left auricle is best seen from behind. It receives on either 

 side two pulmonary veins. The left auricle is somewhat thicker than 

 the right. The left auriculo-ventricular orifice is oval, and a little 

 smaller than that on the right side. 



