VEINS AND HEART. 



possible. Accordingly, we find that the valve 

 consists of plain flaps, supported in the very 

 special and interesting manner shown in the 

 diagram. On the inner walls of the ventricle 

 stand up certain projections of muscle, shaped 

 like ridges or columns, as at L, and M, or of a 

 curious bridge-like form, as at NO. From 

 the tips of these muscular projections small 

 but strong fibrous cords run to various parts 

 of the edges of each flap, where it joins the 

 other flap, and also to numerous points over 

 its ventricular surface. When the ventricle 

 is contracting, and the blood-pressure tends to 

 force the flaps towards the auricle, the support 

 so admirably distributed over the surface of 

 the flaps enables them to hold good against 

 the pressure, and if the valve is not spoiled or 

 the orifice enlarged by disease, no blood is 

 allowed to get back into the auricle, which is 

 meantime collecting a fresh charge from the 

 veins. 



It has just been suggested that sometimes 

 the heart- valves are incapacitated by disease. 

 Similarly the heart-muscle, which does the 

 work of a piston, may be thinned, stretched, 

 and weakened by disease or abuse. To this 

 extent the heart is not a self-repairing pump. 

 But for the wear and tear of ordinary work in 

 good and healthy conditions, these parts are 

 self -repairing, which, of course, the piston and 

 valves of a metallic pump are not. 



297 



