480 Animal Biology 



pany the systemic arteries, frequently having the same names as the 

 arteries. However, many systemic veins are distributed in two sets: (1) 

 deep and superficial veins and (2) special veins, called the portal system, 

 which carry the blood from the digestive tract back to the heart. 



Three systemic veins return blood to the right atrium: (1) the coro- 

 nary sinus (vein) returns blood from the heart walls, (2) superior vena 

 cava (also called precaval vein) returns blood from the head, neck, 



ARCH OF AORTA 



SUPERIOR VFNA CAVA 

 INFERIOR VENA CAVA 



PULMONARY 

 VALVE 



RIGHT 

 AURICLE 



TRICUSPID 

 VALVE 



RIGHT 

 VENTRICLE 



AORTA 



PULMONARY 

 ARTERY 



PULMONARY 

 VEIN 



LEFT AURICLE 



AORTIC VALVE 



MITRAL VALVE 



>LEFT VENTRICLE 



CHORDA TENDINEAE 



Fig. 239. — Human heart shown in longitudinal section. (From Haggard; 

 and His Body; Copyright, 1927, 1938, by Harper & Brothers.) 



Man 



thorax, and upper extremities, and (3) inferior vena cava (postcaval 

 vein) returns it from the abdomen, pelvis, and lower extremities. The 

 superior vena cava is formed by the union of the two innominate veins, 

 and it receives the azygos vein which drains the abdominal region. Each 

 innom,inate vein is formed by the subclavian vein and the internal jugular 

 vein (blood from brain, etc.). The external jugular veins (right and 



