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of fishes and reptiles, but in a less remarkable 

 manner by valves of a most complicated and cu- 

 rious structure, one separating the upper from the 

 lower portion of each cavity of the heart, and one 

 again at the origin of each of the large vessels, 

 going, the one to the lungs, and the other to the 

 body in general. Of these valves it is sufficient 

 to say, in this place, that, while they admit the 

 free passage of the blood in the course which the 

 purposes of the circulation require, they effectu- 

 ally prevent one drop from passing in an oppo- 

 site direction ; and that the structure of these 

 valves alone is sufficient to carry ample evidence 

 to the minds of all but the voluntary blind, of a 

 directing hand, infinite alike in wisdom and in 

 power. The coats of the arteries in birds are 

 thicker and stronger than in other classes of ani- 

 mals, corresponding to the greater energy of the 

 heart. 



The heart of mammiferous animals receives and 

 transmits its blood almost entirely upon the same 

 plan as that of birds ; and is provided with valves of 

 a similar structure, and for the same purpose. The 

 arteries going to the brain of grazing quadrupeds 

 present the peculiarity of being subdivided, and 

 again collected into trunks, before penetrating 

 that organ ; for the obvious purpose of diminish- 

 ing the impulse of the current of blood towards 

 the brain, in those animals in which, from their 

 holding their heads so continually downwards, 

 this impulse is greater than natural. The same 

 peculiarity is observable in the arteries going to 



