1092 



THE THORAX. 



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 

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

 upward. The depression is just above the fossa ovalis in the right auricle. 



To examine the interior of the left ventricle, make an incision a little to the left of the 

 anterior inter ventricular groove from the base to the apex of the heart, and carry it up from 

 thence, a little to the left of the posterior interventricular groove, nearly as far as the auriculo- 

 ventricular groove. 



The Left Ventricle is longer and more conical in shape than the right 

 ventricle. It forms a small part of the left side of the anterior surface of the 



Bristle passed through left 

 auriculo-ventricular opening. 



Passed through aortic opening. 



FIG. 696. The left auricle and ventricle laid open, the posterior walls of both being removed. 



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 side, the proportion being as 3 to 1. They are also thickest 

 in the broadest part of the ventricle, becoming gradually thinner toward the base, 

 and also toward the apex, which is the thinnest part. 



The following parts present themselves for examination within the ventricle : 



f Auriculo-ventricular. ^ T i f Mitral. 



Openmgs-J Anrf .^ Valves^ g emilunar . 



Aortic. 

 Chordae tendinese. 



Columnae carneae. 



The auriculo-ventricular opening is placed below and to the left of the aortic 

 orifice. It is a little smaller than the corresponding aperture of the opposite side, 

 and, like it, is broader in the transverse than in the antero-posterior diameter. It 

 is surrounded by a dense fibrous ring, covered by the lining membrane of the 

 heart, and guarded by the mitral valves. 



The aortic opening is a circular aperture in front and to the right side of the 

 auriculo-ventricular, from which it is separated by one of the segments of the 

 mitral valve. Its orifice is guarded by the semilunar valves. 



