42 THE THORACIC VISCERA, BUCCAL CAVITY, 



opening of the inferior cava, lying between it and the 

 opening of the auricle into the ventricle. Follow 

 its course back along the groove between the auricle 

 and the ventricle. 



d. The Auriculo-ventricular Orifice. The 

 crescentic opening leading into the right v^entricle. 



e. The Left Auricle has thin walls like the right. 

 The walls of the appendix are thicker and marked in- 

 ternally by muscular ridges. 



f. The Left Auriculo-ventricular Orifice. The 

 circular opening leading into the left ventricle. 



2. The Ventricles. 



Cut across the two ventricles at some distance from 

 the apex — in the lower third of the right ventricle. 



The cavity of the right ventricle has a crescentic 

 shape ; the wall is relatively thin. The cavity of the 

 left ventricle is circular ; its walls are quite thick. The 

 ventricular septum is very thick and arched, with the 

 convexity projecting into the cavity of the right ven- 

 tricle. The cavity of the left ventricle extends into 

 the apex, while that of the right ventricle terminates 

 some distance anterior to it. 



Remove the aiiricles close to the base of the ven- 

 tricles, and cnt short the aorta and pulmonary artery. 

 A good view of the relative positions of the four open- 

 ings into the ventricles is tints obtained. 



a. The Tricuspid Valve of the right ventricle. 

 It guards the right auriculo-ventricular orifice, and is 

 formed by three membranous flaps attached round 

 the margin of the orifice. The free borders project 

 into the ventricle, and are connected to its wall by 

 tendinous cords, the chordce tendinecE, which end in 

 papillarv elevations of the ventricular wall known as 

 tht papillary muscles. Some of the chorda^; tendineae 



