1088 THE THORAX. 



cle. The grooves contain the coronary arteries, cardiac veins, lymphatics, nerves, 

 and fat, all covered by the visceral layer of the serous pericardium. 

 Each of these cavities should now be separately examined. 



To examine the interior of the right auricle, an incision should be made along its right bor- 

 der from the entrance of the superior vena cava to that of the inferior. A second cut is to be 

 made from the centre of this first incision to the tip of the auricular appendix, and the flaps 

 raised. 



The Right Auricle is a little larger than the left, its walls somewhat thinner, 

 measuring about one line, and its cavity is capable of containing about two ounces. 

 It consists of two parts a principal cavity, or sinus, venosus or atrium, and an 

 appendix auriculae. 



The sinus is the large quadrangular cavity placed between the two venae cavae ; 

 its walls are extremely thin ; it is connected below with the right ventricle, and 

 internally with the left auricle, being free in the rest of its extent. 



The appendix auricula?, so called from its fancied resemblance to a dog's ear, 

 is a small conical muscular pouch the margins of which present a dentated edge. 

 It projects from the sinus forward and to the left side, overlapping the root of the 

 aorta. 



The internal surface of the right auricle is smooth, except in the appendix and 

 adjacent part of the anterior or right wall of the sinus venosus, where it is thrown 

 into parallel ridges (musculi pectinati). 



It presents the following parts for examination : 



Superior cava. 



Inferior cava. V 1 r / Eustachian. 



Openings \ Coronary sinus. \ Coronary. 



I Foramina Thebesii. 

 (^ Auriculo-ventricular. 



Relics of foetal f Annulus ovalis. 

 structure \ Fossa ovalis. 

 Musculi pectinati. 

 Tuberculum Loweri. 



The superior vena cava returns the blood from the upper half of the body, and 

 opens into the upper and back part of the auricle, the direction of its orifice being 

 downward and forward. 



The inferior vena cava, larger than the superior, returns the blood from the 

 lower half of the body, and opens into the lowest part of the auricle near the 

 septum, the direction of its orifice being upward and inward. The direction of 

 a current of blood through the superior vena cava would consequently be toward 

 the auriculo-ventricular orifice, whilst the direction of the blood through the 

 inferior cava would be toward the auricular septum. This is the normal direction 

 of the two currents in foetal life. 



The tuberculum Loweri is a small projection on the right wall of the auricle, 

 between the two venae cavse. It is most distinct in the hearts of quadrupeds ; in 

 man it is scarcely visible. It was supposed by Lower to direct the blood from the 

 superior cava toward the auriculo-ventricular opening. 



The coronary sinus opens into the auricle, between the inferior vena cava and 

 the auriculo-ventricular opening. It returns the blood from the substance 

 of the heart, and is protected by a semicircular fold of the lining membrane 

 of the auricle, the coronary valve (valve of Thebesius). The sinus, before enter- 

 ing the auricle, is considerably dilated nearly to the size of the end of the little 

 finger. Its wall is partly muscular, and at its junction with the great coronary 

 vein is somewhat constricted and furnished with a valve consisting of two unequal 

 segments. 



Theforamini Thebesii are numerous minute apertures, the mouths of small 

 veins (vena* cordis minima?), which open on various parts of the inner surface of 

 the auricle. They return the blood directly from the muscular substance of the 



