174 NATURAL THEOLOGY. 



This valve, also, is not more curious in its struc- 

 ture, than it is important in its office. Upon the 

 play of the valve, even upon the proportional 

 length of the strings or fibres which check the 

 ascent of the membranes, depends, as it should 

 seem, nothing less than the life itself of the ani- 



and as each of the three valves has a httle sinus behind it, its mar- 

 gin never reaches the wall of the artery. The consequence of 

 which is, that in the instant that the column of blood takes a re- 

 trograde direction, the margins of the valve are caught, and they 

 are thrown up to close the passage. Nothing can be more admi- 

 rably mechanical. 



Since our author has so properly insisted upon the mechanism 

 of the heart as the very strength of his argument, we shall men- 

 tion one circumstance more as showing what may be called the 

 perfection of the workmanship. It has been explained that the 

 valves of the great artery consist oftliree semicircular membranes. 

 Now if we consider the effect of these three semicircles meeting, 

 there must be a triangular space in their centre, an imperfection in 

 the point of their union as it were. To remedy this defect, on the 

 centre of the margin of each valve, there is a little body like a 

 small excrescence or tongue : and when these three bodies meet, 

 they exactly fill up the triangular space which is left in the centre 

 of the three semicircles. It is as if an ingenious workman had 

 contrived a thing the most apposite to remedy a defect. 



