no 



ANATOMY OF THE RABBIT 



licail. nut. liiii//.< 



jugular and subclavian veins, communicating with the right atrium 

 of the heart through paired superior cavals^; from the posterior 



portions of the body through the unpaired 

 and asymmetrical inferior caval vein, the 

 latter passing forward on the right of the 

 median plane and entering the posterior 

 end of the right atrium. The second, 

 short, or pulmonary circulation, is con- 

 cerned with the distribution of the blood to 

 the lungs for purposes of aeration (Fig. 63). 

 It is established by the right ventricle, the 

 pulmonary artery and its paired branches, 

 and the capillaries of the lungs. The 

 blood is delivered to the left atrium through 

 several pulmonary veins. A similar divi- 

 sion of the circulatory organs occurs as a 

 homoplastic modification in birds, which, 

 it will be observed, are also warm-blooded 

 vertebrates. 



In general, the blood which is distribut- 

 valves^""^ '^^* atrioventricular gd to the various parts of the body passes 

 through but one set of capillary vessels, 

 and is then returned through the systemic veins to the heart. In 

 all vertebrates, however, a special portion of the systemic venous 

 circulation is set aside as the hepatic portal system distinguished 

 by the possession of a second series of capillary vessels ramifying 

 in the liver. Thus, in the rabbit and other mammals, the blood 

 distributed to the stomach, spleen, and intestine through the coeliac 

 and the superior and inferior mesenteric arteries, is collected into 

 a main intestinal vessel, the portal vein, and the latter passes to the 

 sinusoids of the liver, which take the place of true capillaries, 

 differing from them as described on page 97. The liver receives 

 also oxygenated blood, though in much smaller quantity, through 

 the hepatic artery and the ultimate branches of this also empty 



bf///r wnlt. pnst. litnbs 



Fig. 61. The mammalian 

 circulation: rv, Iv, right and 

 left ventricles; ra, la, right 

 and left atria; so, sp, semi- 

 lunar valves of aorta and 

 pulmonary artery; vt, vm, 



'In many mammalian species, including man, there is a reduction of the left 

 superior caval vein during development, blood from the left subclavian and jugu- 

 lar vessels all being diverted through the transverse jugular (p. 297) into the 

 right superior caval, which thus appears unpaired in the adult. 



