758 



THE THORAX. 



that the right ventricle forms the greater portion of the anterior surface of the 

 heart, and the left ventricle more of its posterior surface. 



Each of these cavities should now be separately examined. 



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, and an appendix 

 auriculae. 



The sinus is the large quadrangular cavity, placed between the two vena? cava? ; 

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

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





 Fig. 419. The Bight Auricle aud Ventricle laid open, the Auterior Walls of both being removed. 



Sigkt Au ritula \mtricu Inr 



The appendix auriculse, 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 forwards and to the left side, overlapping the root of 

 the pulmonary artery. 



To examine the interior of the auricle, a transverse incision should be made along its ventricular 

 iiiiir^-in, from its right border to the appendix ; and, from the middle of this, a second incision 

 should be carried upwards, along the inner side of the two vena; cava;. 



The following parts present themselves for examination : 



Openings. - 



Superior cava. 

 Inferior cava. 

 Coronary sinus. 



Valves. 



Foramina Thebesii. 

 A uriculo-ventricular. 

 Relics of fostal j Annulus ovalis. 

 structure. ( Fossa ovalis. 

 Musculi pectinati. 



j Eustachian. 

 ( Coronary. 



