THE CIRCULATORY SYSTEM. 



431 



Aneurisms of the valves are formed in two ways: 



1. They are the result of endocarditis. One of the lamellae of the 

 leaf of a valve is destroyed, and the other lamella is converted into a sac 

 filled with blood. These aneurisms are found in the aortic valve, pro- 

 jecting into the ventricle ; and in the mitral valve, projecting into the 

 auricle. Not infrequently the wall of the aneurism gives way, so that 

 there is a rupture entirely through the valve. 



2. The entire thickness of a leaf of a valve is pouched, forming a sac 

 filled with blood. This occurs in the aortic, mitral, and tricuspid valves. 



Haemorrhage in the substance of the valves is sometimes found in very 

 young children. 



ANEURISM OF THE HEART. 



Sacs filled with blood, situated in the walls of the heart and communi- 

 cating with its cavities, are formed in several different ways. 



1. In interstitial myocarditis a small or large portion of the wall may 

 be replaced by fibrous tissue, and this yielding to the pressure of the 

 blood from within, may be pressed outward. Such a pouch may be a 

 circumscribed sac communicating with the heart cavity by a small open- 



FIG. 227. - ANEURISM OF THE HEART OPENING FROM THE LEFT VENTRICLE INTO THE RIGHT AURICLE. 

 Seen from behind. 



