146 



ADVANCED PHYSIOLOGY 



teries away from the heart, he finds that they branch re- 

 peatedly until at the ends of the arms, in the head, skin or 

 (ntestine, they are extremely small. The smallest subdivisions 

 of the blood vessels are called capillaries. Soon these minute 



tubes unite as veins, 

 which as they go to- 

 ward the heart are 

 joined by others and 

 finally are even larger 

 than the arteries. 



The Arteries. - 

 From the right ventri- 

 cle, the blood enters 

 the pulmonary artery ; 

 Fig. 74. This artery 

 divides, sending one 



-~&9SpkA>n branch t0 6ach lung ' 



..^-^uperioritleKnteric and inside the lungs 



each branch divides 

 into numerous small- 

 er branches; finally, 

 each minute twig 

 breaks up into a pro- 

 fusion of lung capil- 

 laries. In these capil- 

 laries the blood takes 

 up and gives off 

 gases. After passing 

 through the capilla- 

 ries, the blood collects 

 in veins which unite 

 to form large trunks, that finally leave the lungs, going 

 immediately into the left auricle; Fig. 76. From here, the 

 blood goes to the left ventricle, and thence out through 

 an artery, the aorta: Fig. 76. 



FIG. 78. DIAGRAM 



Showing the aorta and its chief branches. The 

 broken line runs through the middle of the aorta. 



