Chap. III.] 



GENERAL ANATOMY. 



27 



direct from the heart are called arteries. When they reach the 

 organ they supply, they branch again and again, and eventually 

 break up into minute tubes called capillaries. Then these unite 



ex. ju. 



an. aV. 



d.ao. 



-c. 



v - m 



Fio. 10. HEART AND SOME GREAT VESSELS OF FROG. 



with each other, and by repeated union give rise to larger blood- 

 vessels, which lead the blood away from the organ. These are 

 called veins. So that we have the series, (1) artery, (2) capil- 

 lary plexus, (3) vein. Where two blood-vessels unite to form a 

 common trunk they should be called factors ; and where a trunk 

 splits into two vessels they should be called branches. 



The blood carried to the lungs by the pulmonary artery is 

 returned thence to the left auricle of the heart by the pulmonary 

 vein. The blood supplied to the head and fore-limbs is returned 

 to the sinus venosus by (precaval) veins (10, pr. c.), of which that 

 on the left side is shown in Fig. 7, that on the right side being 

 removed. This vein is seen to be made up of three factors 

 (external jugular, ex. ju.; innominate, in.; subdavian, s. cl.). The 

 blood from the hind-limbs may take one of two courses, either 

 by the anterior abdominal vein (ant. ab.\ in which case it passes 

 to the liver, and there breaks up into a capillary plexus, or by 



