1 68 



The Heart 



intercostal spaces, being behind, and a little to the left of the tricuspid 

 valve. The two flaps of the mitral valve are unequal, the larger and 

 stronger being placed to the right and in front, between the auriculo- 

 ventricular and the aortic openings. The segments are connected 

 with musculi papillares as in the right ventricle. 



The aortic orifice is to the front of the ventricle and to the right 

 of the opening into the auricle. It is behind the sternal end of the 

 third left space, and is guarded by semilunar valves, like those at the 

 root of the pulmonary artery, than which, however, they are larger 

 and stronger. It is behind, and a little to the left of, the pulmonary 

 orifice. 



The semilunar valves are folds of the lining membrane of the heart 

 over a foundation of fibrous tissue ; at the middle of the free border 

 of each is a fibrous nodule, the corpus Arantii. These nodules block 

 the centre of the aperture during diastole, when the valves fall to- 

 gether. The closed valve does not form a horizontal plane across the 

 root of the artery ; the convex surfaces of its segments bulge against 

 each other, and, the greater the strain, the greater the surfaces of con- 

 tact and the less the chance of regurgitation. 



The sinus of Valsalva is the dilated part of the artery behind the 

 segments of the valve. When the ventricle ceases contracting, the 

 elasticity of the artery drives the blood into the three sinuses and 

 forces the valves together. 



The coronary arteries are given off from the sinuses of Valsalva. 

 The right comes forward on the right side of the pulmonary artery, and 

 winds round the right auriculo-ventricular sulcus, sending one branch 

 down the posterior inter-ventricular groove to the apex, and another 



1, Right ventricle. 



2, Left ventricle. 



3 and 4, Parts of right and 

 of left auricles. 



5, Tricuspid valve. 



6, Mitral valve. 



7, Pulmonary artery. 



8, Aorta. 



9, Coronary artery. 



between the back of the left auricle and ventricle. The left coronary 

 artery passes on the other side of the pulmonary artery, down the anterior 



