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 

 auriculas. 



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





 Fig. 419. The Eight Auricle and Ventricle laid open, the Anterior Walls of both being removed. 



Brittle yatsed tk 



Bight Au.ricu.lu \'intric,t!a,- Cftnitiy 



The appendix auriculae, 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 

 margin, 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 venae cavae. 



The following parts present themselves for examination : 



f Superior cava. 

 Inferior cava. ( T^t^; 



y~. ,-, . -i~r 1 i JBlUoWvIlUsm 



Openings. -^ Coronary sinus. Valves, j Coronary 



Foramina Thebesii. J ' 



[ Auriculo-ventricular. 

 Kelics of foetal j Annulus ovalis. 

 structure. ( Fossa ovalis. 

 Musculi pectinati. 



