9^4 



A MANUAL OF ANATOMY 



the centre of the border there is a small swelling, called the nodule 

 or corpus Arantii. This gives rise to a slight projection, and on either 

 side of it the border is concave. The attached convex border of 

 each segment is also strengthened by fibrous tissue. In addition 

 to these fibrous thickenings, fibrous tissue pervades each segment 

 from the nodule to the attached border, with the exception of 

 the portions immediately below the lateral concave parts of the 

 free border. These portions, in each segment, are semilunar, and 

 are called the lumtlce. They are the thinnest parts of the segment, 

 and are transparent, consisting prac- 

 tically of endocardium and the endo- 

 thelial lining of the artery. 



The interior of the wall of the 

 aorta presents three well - marked 

 recesses, each of which is placed 

 opposite a segment of the valve. 

 These recesses are called the sinuses 

 of Valsalva, and they are disposed 

 as right antero-lateral, left antero- 

 lateral, and posterior, respectively. 

 The right antero-lateral sinus of 

 Valsalva presents the orifice of the 

 right coronary artery, and the left 

 antero-lateral sinus of Valsalva pre- 

 sents the orifice of the left coronary 

 artery. Each sinus of Valsalva, 

 together with the corresponding 

 segment of the aortic valve, forms 

 a small pocket, and the three pockets open away from the left 

 ventricle, that is to say, in a direction corresponding to the normal 

 blood-flow. 



Function of the Aortic Valve. — This valve serves to prevent regurgitation of 

 blood from the aorta into the left ventricle during the elastic recoil of the arterial 

 wall close to the heart. During the ventricular systole, when the blood is being 

 driven through the aortic orifice, the aortic valve is passive, and its three seg- 

 ments are applied to the arterial wall. During the elastic recoil of the arterial 

 wall, however, the valve is in action. The first effect of the elastic recoil is 

 to force sufficient blood backwards towards the left ventricle to close the 

 aortic valve. This blood enters the pockets formed by the sinuses of Valsalva 

 and the segments of the valve. The segments are pressed towards the centre 

 of the aortic orifice, and they come into contact in the following manner: 

 the three nodules or corpora Arantii come into close contact at the centre of 

 the aortic orifice, and so close what would otherwise be a small space, and 

 the respective lunula; are closely pressed against one another. In this manner 

 the aortic orifice is completely closed, and regurgitation of blood into the left 

 ventricle is, in health, effectually guarded against. It will be evident that 

 the strain of the backward pressure of blood must be borne by those portions 

 of the segments which are strengthened by fibrous tissue extending from each 

 ijodule to the attached border of each segment. Though the lunul.Te are thin 

 and weak, nevertheless, being, so to speak, doubled up against one another, 

 the more they are pressed upon the more closely they fit together. 



When the aortic valve offers opposition to the entrance of blood into the 

 aorta, the cardiac affection is called aortic obstruction (stenosis). On the 



Fig. 405. — The Semilunar 

 Valves of the Aorta 

 (Superior View). 



I, Left Antero-lateral Sinus 

 of Valsalva ; 2, Right Antero- 

 lateral Sinus of Valsalva; 



3, Posterior Sinus of Valsalva ; 



4, Right Coronary Artery ; 



5, Left Coronary Artery. 



