lOO ANATOMY OF THE RABBIT 



epigastric regions. Important anastomoses with epigastric, 

 phrenic, and intercostal arteries occur. 



40. Intercostal aa. : Thoracic aorta; to parieties of thorax, 

 some seven pairs; the first passes between the fifth and sixth 

 ribs. The first, or anterior, three pairs extend decidedly laterad 

 and some anastomose with branches of the internal mammary 

 (39). The next three pairs extend much more nearly directly 

 laterad before entering the intercostal spaces, while the seventh 

 pair may loose its identity by being paired, single or branched 

 and passing dorsad as do the lumbars (46). 



41. Phrenic a.: Aorta, usually; to diaphragm. Commonly 

 two pairs, sometimes additional branches pass from the last 

 pair of intercostals and other arteries. 



C. THE VENAE CAVAE 



(Figs. 27, 29) 



Roughly speaking that portion of the systemic venous system 

 lying craniad to the heart comprises the precaval system, 

 while that portion of the systemic venous system lying caudad 

 to the heart comprises the postcaval system. Unlike man, 

 the rabbit has two superior venae cavae, a right and a left, which 

 converge with each other and the inferior vena cava at the 

 sinusvenosus of the right auricle. 



Vena cava superior (precava; Fig. 27): Confluence of the 

 jugular and subclavian veins of the left side forms a trunk, the 

 left precava, which is comparable to the left innominate 

 (left brachiocephalic) vein in man, but unlike the innominate 

 of man it empties directly into the sinus of the right auricle 

 without joining the right vein to form a common trunk (vena 

 cava superior). The right precava is formed as is the left, 

 except that near the right auricle it receives the azygos vein. 

 Thus, the principal paired tributaries of the superior venae 

 cavae are the subclavian, internal, and external jugulars, 

 internal mammary (sternal) and supreme intercostal 

 veins. 



