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A MANUAL OF ANATOMY 



situated on the left and posteriorly, whilst the aortic orifice is 

 situated on the right and anteriorly. The aortic orifice is also the 

 higher of the two. Vence minimce cordis are said to open into the 

 left ventricle. 



The auriculo-ventricular, or mitral, orifice is oval, and, in health, 

 it admits two fingers held side by side. It allows the arterial blood 

 to flow from the left auricle into the left ventricle, and, in order to 

 prevent regurgitation of blood from the ventricle into the auricle 

 during the ventricular systole, it is guarded by an important valve. 

 This valve is called the left auriculo-ventricular, mitral, or bicuspid 

 valve. It is composed of two large segments or cusps, with two 

 small cusps in the angular intervals between their basal parts. The 

 cusps are similar in shape and structure to those of the tricuspid 

 valve, but, on account of the nature of their work, they are thicker 

 and stronger. They are disposed obliquely, and are of unequal 



Pulmonary Orifice and Valves 



Left Coronary Artery.^ 



Left Ventricle- 



Section of Left Auricle 



Mitral Orifice and Valve | 



Secondary Segment of Mitral Valve 



Aortic Orifice and Valves 



Right Coronary Artery 



^.... Right Ventricle 



Tricuspid Orifice and Valve 

 I 

 Section of Right Auricle 



Fig. 403. — TrtE Auriculo-Ventricular and Arterial Orifices of the 

 Heart, with their Valves (Superior View). 



(The Auricles have been removed.) 



size. The larger of the two is placed in front, and to the right, 

 of the orifice. It intervenes between the auriculo-ventricular and 

 aortic orifices, and is known as the anterior or aortic cusp. The 

 smaller cusp is placed behind, and to the left, of the orifice, and 

 is known as the posterior or marginal cusp. 



The chordae tendinese are attached to the cusps, as in the case of 

 the tricuspid valve. They are, however, fewer in number, and of 

 greater thickness and strength, than on the right side. 



Function of the Tricuspid and Mitral Valves. — These valves serve to prevent 

 regurgitation of blood from the ventricles into the auricles during the 

 ventricular systole. Whilst the ventricle is being filled, some of the blood 

 gets behind the segments of the auriculo-ventricular valve, that is to say, 

 between each segment and the wall of the ventricle, and the segments are 

 thus carried towards the auriculo-ventricular orifice. When the ventricle is 



