CIRCULATION OF THE BT.OOD 



11. The veins present a similar disposition, but which is de- 

 signed to produce an entirely opposite result, because the blood 

 in these vessels, pursues an inverse course. They are very 

 numerous at a distance from the heart, but, little by little, they 

 unite to form larger canals which, in turn, again unite, so that 

 they terminate at the heart, in only one or two large trunks. 



12. The ultimate rami- 

 fications of the arteries in 

 the substance of the or- 

 gans, are continued into 

 the radicles of the veins, 

 so as to form a series of 

 uninterrupted and narrow 

 canals through which the 

 blood passes through the 

 organs. 



^13. To these delicate 

 canals, which establish the 

 communication between 

 the termination of the arte- 

 ries and the beginning o[ 

 the veins, is applied to the 

 name of capillary vessels, 

 (Fig. 4.) This name has 

 been given to them in 

 consideration of their ex- 

 treme fineness, which 

 makes them comparable 

 to hairs.* 



Fig. 4. 



Explanation of Fig-. 4. This figure does not represent the natural 

 arrangement of the heart and blood vessels; it is an ideal diagram, 

 designed to convey some notion of the way in which the blood, in completing 

 the entire route of the circulation, passes twice through the heart, and also 

 passes through the two systems of capillary vessels, namely, those of the 

 lungs in getting from the pulmonary artery into the pulmonary veins, and 

 those of all the organs, in passing from the minute terminating branches or 

 the aorta, into the radicals of the veins which end in the venae cavse. The 

 two halves of the heart, which in reality, are only separated by a partition, 

 are here completely isolated, ^, left side of the heart, a, the aorta, e, o, p, 

 capillary vessels, which terminate the arteries, all of which spring from the 

 aorta, , general venous system, rf, right side of the heart, a,p, pulmo 

 nary artery, v,p, pulmonary vein. The arrows po'nt in the direction o/ 

 ihe current. 



11. How are the veins arranged? 



12. How do the ultimate ramification of the arteries terminate? 



13. What are the capillary vessels ? Why are they so called ? 



E 



