203 



cafe with each ventricle. The artery,* which commu- 

 nicates with the right ventricle, conveys the blood to the 

 lungs. The vein/t which communicates wit'i -the same 

 ventiicle, forms the principal trunk of the veins, and 

 carries back the blood from all parts to the heart. The 

 artery, J which goes intft the left ventricle, is the chief 

 trunk of the arteries, and that which conveys the blood 

 to all parts. The vein,|| which ends at the same ven- 

 tricle, transmits to it the blood tkat has been conveyed 

 from the lungs. 



The principle trunks of veins and arteries, are divided 

 into several branches at a small distance from the heart. 

 Some tend towards the upper extremities, others to- 

 wards tl>e inferior. 



The arteries and veins decrease in diameter, and are 

 ramified more or less according to their distance from 

 their origin. There is no part to which these do not 

 distribute one or more ramifications. 



When they have arrived at the most remote parts, the 

 arteries have au intercourse with the veins. 



The arteries are composed of several membranes, 

 placed ou each other. The veins have similar mem- 

 branes, but more slender, and weaker. The veins were 

 j;.rt designed to exercise the same power as the arteries. 

 These latter must necessarily, like the heart, and for the 

 same end, dilate and contract themselves : they have 

 therefore been provided with a very elastic membrane. 

 Tiie exercise of the veins should not be violent. 



At the root of the arteries, and in the inner part of 

 the veins, are placed little sluices or valves, which by 

 sinking and rising again open and shut the caned. These 

 valves are deposited in the veins, in a contrary sense 

 from that for which they are in the arteries. We shall 

 presently account for the cause of this difference. 



20. After having been masticated and dissolved in the 



* The pulmonary artery, f The vena cava. J The grand rtrry, 

 or the aorta, H The pulmonary vein. 



