240 ANATOMY IN A NUTSHELL. 



The right auricle has a capacity of about two ounces. It is larger than the 

 left auricle but its walls arc thinner. It consists of two main parts, first a sinus 

 or atrium which is large and lies between the superior vena cava above and the 

 inferior vena cava below and has postero-internally to it the left auricle. The 

 second pari is the auricular appendix, which is small and conical projecting for- 

 ward and to the left over the root of the aorta. The inner surface of the auricle 

 is smooth except in this auricular appendix and the adjacent part of the right 

 wall of the sinus. At this point it is thrown into parallel ridges called musculi 

 pectinati. (Plate CXXIX.) 



The right auricle has the following points for consideration: 



1. The opening of the superior vena cava, which is at the upper and back 

 part of the auricle and is directed downward and forward. The blood from the 

 superior vena cava flows toward the auriculo-ventricular opening. 



2. The opening of the inferior vena cava is larger than the superior and is 

 at the lower part of the auricle near the auricular septum. The blood from the 

 inferior vena cava is directed upward and inward towards the auricular septum. 



3. There is small projection between the superior vena cava and the in- 

 ferior vena cava called the tubercle of Lower. Its function is to direct the blood 

 from the superior vena cava towards the auriculo-ventricular opening. 



4. There is an opening between the inferior vena cava and the auriculo- 

 ventricular opening called the coronary sinus. It is guarded by a valve called 

 coronary or Thebesii. It receives blood from the substance of the heart and it 

 is constricted where it joins the great coronary vein. 



5. The auriculo-ventricular opening is somewhat oval and about an inch 

 in diameter and lies between the right auricle and right ventricle. It is sur- 

 rounded by a fibrous ring covered by the lining membrane and is guarded by 

 the Tricuspid valve. 



6. The foramina of Thebesii are small openings of the venae cordis minima? 

 which return blood from the substance of the heart. 



7. A semilunar fold of the endocardium which lies between the auriculo- 

 ventricular opening and the anterior margin of the opening of the inferior vena 

 cava is called the Eustachian valve. In the fetus this valve is large and directs 

 the blood from the inferior vena cava through the foramen ovale into the left 

 auricle. It may be present or it may be absent in the adult. 



8. The coronary valve also called Thebesii is a semicircular fold of endo- 

 cardium which guards the opening of the coronary sinus. This valve may be 

 double and it prevents regurgitation into it (hiring systole 1 of the auricle. 



9. The fossa ovalis is a remains of fetal life. It is an oval depression lying 

 on the lower part of the auricular septum marking the position of the foramen 

 ovale. There may be a small foramen in this fossa throughout life. 



10. The annulus ovalis is a prominent margin of the foramen ovale and is 

 best marked above and at the sides, while below it is wanting. 



11. The musculi pectinati are small muscular folds which are found in the 

 auricular appendix and the adjacent pari of the sinus venosum. They end in 

 a vertical ridge posteriorly called the crista terminalis of His. 



The right venrtiele extends from the right auricle nearly to the apex of the 



