THE VASCULAR SYSTEM (Continued) 



VEINS POSTERIOR TO THE HEART * 



Blood from the parts of the rat posterior to the heart 

 enters the right auricle through the inferior vena cava 

 (post cava). Trace the vena cava caudally to the dia- 

 phragm, which it pierces, then enters the abdominal cavity. 

 In the thoracic cavity the vein is surrounded by the lobes 

 of the lungs, and lies at the right of the esophagus. 



Study the structure and attachments of the diaphragm. 

 It comprises a central V-shaped tendinous portion, sur- 

 rounding which is a muscular region with fibers radiating 

 from the central tendon to the adjacent body walls. Note 

 the relative positions of the apertures through which the 

 inferior vena cava, esophagus, and descending aorta pene- 

 trate the diaphragm. Observe the number and distribu- 

 tion of the phrenic veins which traverse the diaphragm, 

 carrying blood from its substance to the inferior vena cava. 

 Follow the inferior vena cava posteriorly from the dia- 

 phragm, exposing its tributaries, which are described 

 below. 



The hepatic veins convey the blood from the liver, which 

 received it from the portal circulation and hepatic artery, 

 to the inferior vena cava. The hepatic veins may be ex- 

 posed by carefully chipping away the brittle tissue of the 

 liver with a blunt instrument. Determine the number and 

 location of these veins. The two renal veins, short but of 

 large calibre, drain the blood from the kidneys into the 



* Locate the sympathetic nervous system before dissecting the 

 arteries and veins posterior to the heart. This system will probably 

 be injured during the dissection. 



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