DISEASES OF THE HEART.-— ENDOCARDITIS. 285 



and the wall of the vessel, than does the ^' line of contact." The 

 free border of the valve therefore acts as a retinaculum in 

 exactly the same way as the chordsB tendinea) of the cuspid 

 valves. For the performance of this function it is clear that all 

 that part of the surface of the valve which lies between the free 

 border and the ^' line of contact," is superfluous. Hence the 

 disappearance of this intermediate portion (only a few connecting 

 strips of it being left) is an acknowledgment of the functional 

 independence of the free border. 



In extreme cases (which are not, upon the whole, rare) of 

 marginal perforation of the valves, a nearer approximation of 

 the sigmoid to the cuspid type is brought about by the existence 

 of an interval between the point at which the marginal part of 

 the valve is attached to the wall of the vessel, and the point at 



Fig. 88. 



Fenestrated semilunar valves from the pulmonary artery. 

 ^Natural size. 



which its ^' line of contact " is attached. So that the correspond- 

 ing halves of the free borders of any two contiguous flaps, 

 together with the fine threads which link them with the " line of 

 contact," spring from a point of the arterial wall above the real 

 insertion of the valve. This interval between the points of 

 attachment of the retinacula of the valve-flaps, and that trans- 

 verse plane of the vessel which it is the business of the valve to 

 close (making it possible to retain the valves in a more vertical, 

 and therefore in a more secure position), is the fundamental 

 principle of the cuspid type of structure. Fig. 88 represents an 

 extreme example of perforation of the sigmoid valves ; the 

 bundles of tendinous threads stretched over the glass rod, which 



