348 OUTLINES OF CHORDATE DEVELOPMENT 



vein connects with the right posterior cardinal vein. The 

 posterior cardinal veins pass along the dorsal side of the kid- 

 neys (mesonephroi, see below) receiving their vessels. But 

 during the fourth day a system of venous spaces appears on the 

 ventral side of the kidney; these vessels are known as the sub- 

 cardinal veins (Fig. 138). During the sixth day the inferior 



pc dv 



8V * t v 



^^^^ LJH^V wa v a - 

 aJ 



FIG. 138. Diagrammatic lateral view of the chief embryonic blood-vessels 

 of the chick, during the sixth day. After Lillie. a. Auricle; al, allantoic stalk; 

 ao, dorsal aorta; c, cceliac artery; ca, caudal artery; cl, cloaca; cv, caudal vein; 

 da, ductus arteriosus; dv, ductus venosus; ec, external carotid artery; ej, external 

 jugular vein; i, intestine; ic, internal carotid artery; ij, internal jugular vein; 

 I, liver; ra, mesonephros; ma, mesenteric artery; mv, mesenteric vein; p, pulmonary 

 artery; pc, posterior cardinal vein; pv, pulmonary vein; s, sciatic artery; sc, 

 subclavian artery; SCT, subclavian vein; st, yolk-stalk; sv, subcardinal vein; 

 ul, left umbilical artery; ur, right umbilical artery; uv, left umbilical vein; v, 

 ventricle; va, vitelline artery; vca, anterior vena cava (anterior cardinal vein); 

 vp, posterior vena cava; vv, vitelline vein; y, yolk-sac; 3, 4, 6, third, fourth, and 

 sixth aortic arches. 



vena cava connects with the right subcardinal vein, the two 

 subcardinal veins anastomose posterior to this connection, and 

 the anterior parts of both posterior cardinal veins disappear. 

 The net result of these changes is that the hinder parts of the 

 posterior cardinals form the afferent renal trunks or renal portal 

 veins, the subcardinals form the efferent renal vessels leading into 

 the inferior vena cava, through which all of the blood from the 

 embryonic kidneys (mesonephroi) is returned directly to the 



