THE CIRCULATION OP THE BLOOD. 

 Fig. 3. 



261 



The Arterial system. 



vena cava. The other conveys the scarlet-coloured or arte- 

 rial blood, from the lungs to the left auricle, into which it 

 issues by four large trunks, called pulmonary veinsj The 

 veins are strong and flexible, but not elastic like arteries. 

 They are furnished with little valves placed at short dis- 

 tances from each other, so as to prevent the blood from flow- 



