696 THE THORAX. 



The pulmonary veins, four in number, open, two into the right, and two into 

 the left side of the auricle. The two left veins frequently terminate by a common 

 opening. They are not provided with valves. 



The auricula-ventricular opening is the large oval aperture of communication 

 between the auricle and ventricle. It is rather smaller than the corresponding 

 opening on the opposite side. 



The musculi pectinati are fewer in number and smaller than on the right side ; 

 they are confined to the inner surface of the appendix. 



On the inner surface of the septum auricularum may be seen a lunated impres- 

 sion, bounded below by a crescentic ridge, the concavity of which is turned 

 upwards. This depression is just above the fossa ovalis in the right auricle. 



Fig. 353. The Left Auricle and Ventricle laid open, 

 the Anterior Walls of both being removed. 



passed thro' Aortic opening 



The LEFT YENTKICLE is longer and more conical in shape than the right ven- 

 tricle. It forms a small part of the left side of the anterior surface of the heart, 

 and a considerable part of its posterior surface. It also forms the apex of the 

 heart by its projection beyond the right ventricle. Its walls are much thicker 

 than those of the right ventricle, the proportion being as 2 to 1 (Bizot). They 

 are also thickest in the broadest part of the ventricle, becoming gradually thinner 

 towards the base, and also towards the apex, which is the thinnest part. 



Its cavity should be opened by making an incision through its anterior wall along the left side 

 of the ventricular septum, and carrying it round the apex and along its posterior surface to the 

 auriculo-ventricular opening. 



The following parts present themselves for examination : 



~ . ( Auriculo-ventricular. -vr -, ( Mitral. 



Openings j Aortia Valves j Semilunan 



Chordae tendinea?. Columnas carneas. 



