364 



THE HEART. 



The arterial or aortic orifice, circular in form, and smaller than the auricular, is 

 separated from it only by the attachment of the anterior segment of the mitral valve. 

 As in the pulmonary artery, its valve consists of three semicircular flaps (semilunar 

 or sigmoid) (fig. 314, II), each of which is attached by its convex border to the side 

 of the artery at the place where it joins the ventricle, while its other border, nearly 

 straight, is free, and projects into the interior of the vessel. 



The segments of these valves are composed of fibrous tissue covered by a 

 prolongation of the endocardium on the one side, and of the inner coat of the 

 artery on the other side. Their thickness varies at different parts. A tendinous 

 band strengthens the free edge of the valve, and at the middle of that margin 



Fig. 317. THE INTERIOR OP THE VENTRICLES OP THE HEART, PROM BEHIND, SHOWING THE MODE OP 



ORIGIN OP THE AORTA, THE MEMBRANOUS PART OP THE INTERVENTRICULAR SEPTUM, &C. (His.) f 



there is a slight thickening, the nodulus or corpus Arantii (fig. 315, 3). Other 

 tendinous fibres, arising from the attached border, run in the valve towards the 

 nodule, occupying its whole extent, except two narrow lunated portions, one on 

 each side, adjoining the free margin of the valve. These parts, which are named 

 lunulce, are therefore thinner than the rest. There is also a strengthening fibrous 

 band along the attached border of each valve. The wall both of the aorta and 

 pulmonary artery is bulged out opposite each semilunar flap : these bulgings are 

 known as the sinuses of Valsalva. In the aorta these are situated one anteriorly 

 and two posteriorly (right and left). From the anterior arises the right coronary 

 artery, and from the left posterior the left coronary artery, these vessels being for 

 the supply of blood to the substance of the heart. 



The capacity of the sinuses of Valsalva is greater, and the tendinous tissue in 



