Part II. in /y6^ Great ion. 273 



rits, the Inftrumenrs of all Senfe and Motion. 

 Now for this Ufe of receiving and pumping out 

 of the Blood, the Heart is admirably contrived. 

 For, Firfl^ being a mufcular Part, the Sides of it 

 are composed of two Orders of Fibres, running 

 circularly or fpirally from Bafe to Tip, contra- 

 rily one to the other, and fo being drawn or con- 

 trad:ed contrary ways, do violently conftringe 

 ai^ ftraiten the Ventricles, and ftrongly force 

 out the Blood, as we have formerly intimated ; 

 then the Veffels vi^e call Arteries^ which carry 

 from the Pleart to the feveral Parts, have Valves, 

 v^hich open outwards, like Trap-doors, and give 

 the Blood a free Paffage out of the Heart, but 

 will not fufFer it to return back again thither; 

 and tlie Veins^ which bring it back from the 

 feveral Members to the Heart, have Valves or 

 Trap-doors, which open inwards, fo as to give 

 way unto the Blood to run into the Heart, but 

 prevent it from running back again that way ; 

 befides, the Arteries confift of a quadruple Coar, 

 the third of which is made up of annular or or- 

 bicular carneous Fibres to a good thicknefs, and 

 is of a mufcular nature, after every Pulfe of the 

 Heart, ferving to contrad the Veffel fucceflively 

 with incredible Celerity, fo by a kind of periftal- 

 tick Motion impelling the Blood onwards to the 

 capillary Extremities and thro' the Mufcles with 

 great Force and Swiftnefs 3 fo the Pulfe of -the 

 Arte/ies is not only caus'd by the Pulfation of the 

 Heart driving the Blood thro* them in manner 



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