NATURAL THEOLOGY. 173 



pying the passage, prevents the return of the blood 

 into the auricle. A shorter account of the matter 

 may be this : so long as the blood proceeds in its 

 proper course, the membranes which compose 

 the valve are pressed close to the side of the ves- 

 sel, and occasion no impediment to the circula- 

 tion: when the blood would regurgitate, they are 

 raised from the side of the vessel, and, meeting in 

 the middle of its cavity, shut up the channel. 

 Can any one doubt of contrivance here; or is it 

 possible to shut our eyes against the proof of it V 



NO 



■*" We cannot resist following up these observations with some 

 minute notices of the appropriate structure. A sail distended 

 with the wind would be torn up, were not the margins secured : 

 accordingly, the canvass is folded over a strong cord, which is 

 called the bolt-rope. So the margins of these semi-lunar valves 

 are as finely finished as any sheet from the dock-yard. There is 

 a ligament which runs along the margin, and strengthens it to 

 sustain the impulse of the back-stroke of the artery. And were 

 those cordoi tendinece, which we have described as like the leeches 

 of a sail, attached to the corner of the mitral valve without further 

 security, they would be torn off on the first pulsation. But as the 

 leeches are secured to the bolt-ropes of the sail, so are the corda 

 tendmece continued into firm ligamentous cords which strengthen 

 the valves. J 



Our author says well, that the valve is thrown down on the side 

 of the artery when the blood is in its course. But were this really 

 the case, the refluent blood would not easily catch the edge of the 

 valve to throw it up. Now this difficulty is met very curiously, 

 and in two different modes. The cordae tendin(B prevent the 

 margins of the mitral valve within the ventricle from flapping close 

 against the side of the cavity; and as to the semi-lunar valves, at 

 the root of the great artery, they are prevented falling against the 

 walls in another mode : the section of the artery at its root is not 

 a regular circle ; but it is formed into three little bags or sinusee, 



15* 



