344 



HISTORY OF THE HUMAN BODY 



from the end of the tail, between the kidneys, to the heart. 

 The remainder of the posterior cardinals, anterior to the con- 

 nection with the vena cava, becomes reduced in proportion 

 to the loss of function and the two remain either as small 

 but continuous vessels, as in the Amphibia, or as the azygos 

 veins, which continue to play a subordinate role by collecting 



a 



FIG. 97. Development of the postcava and the hepatic portal system 

 in the lizard (Lacerta}. [After HOCHSTETTER.] 



The figures (a) to (e) represent consecutive stages of development. s, sinus 

 venosus; c, c, ductus Cuvieri; ud, right umbilical vein; us, left umbilical vein; omd, 

 right omphalo-mesenteric vein; oms, left omphalo-mesenteric vein; pc, postcava; i, 

 intestine; x v x z , x v commissures between the veins of the two sides. 



the blood from the sides of the trunk, especially from the 

 intrrrostnl sprvrf^ a function which they exercise in gauropsids 

 and mammals. 



Fig. 98 shows the development of the postcava in a mam- 

 mal in which the part played by the posterior cardinals is 

 especially emphasized. In some details the developmental 



