692 



THE THORAX. 



Each of these cavities should now be separately examined. 



The EIGHT AUEICLE 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-shaped cavity, placed between the two 

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



Fig. 352. The Right Auricle and Ventricle laid open, 

 the anterior walls of both beiuR removed. 



Xn'sflf paffflf til 



Sly he Auricula Ytntficu far eptviti 



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

 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 ventri- 

 cular margin, from its right border to the appendix ; and, from the middle of this, a second inci- 

 sion should be carried upwards, along the inner side of the two venaj cavas. 



The following parts present themselves for examination : 



Eelics of Foetal j Annulus ovalis. 



structure. } Fossa ovalis. 

 Musculi pectinati. 



vr , ( Eustachian. 



Valves. 



Openings. 



Superior vena cava. 

 Inferior vena cava. 

 Coronary sinus. 

 Foramina Thebesii. 

 Auriculo-ventricular. 



Coronary. 



