THE FCETAL CIRCULATION. 



J B C 



275 



FIG. 219, A, B, C. DIAGRAM OF THE DEVELOPMENT OF THE PAIRED VENOUS 

 SYSTEM OF MAMMALS (MAN). (From Gegenbaur.) 



A. Stage in which the cardinal veins have already disappeared. Their position is 



indicated by dotted lines. 

 B. Later stage, when the blood from the left jugular vein is carried into the right 



to form the single precaval ; a remnant of the left precaval however still 



remains. 

 C. Stage after the left vertebral vein has disappeared, the right vertebral remaining 



as the azygos vein. The coronary vein remains as the last remnant of the left 



precaval. 

 /, jugular vein ; cs, precaval, s, subclavian veins ; c, posterior cardinal vein ; v, 



vertebral vein ; az, azygos vein ; cor, coronary vein. 



FIG. 219, D. DIAGRAM OF THE CHIEF VENOUS TRUNKS OF MAN. 

 (From Gegenbaur. ) 



os, precaval ; s, subclavian vein ; ji, internal jugular ; je, external jugular ; az, 

 ,-. azygos vein; ha, hemiazygos vein; c, dotted line showing previous position 



of'cardinal veins ; ci, postcaval ; r, renal veins ; il, iliac ; hy, hypogastric veins ; 



h, hepatic veins. The dotted lines show the position of embryonic vessels 



aborted in the adult. 



entirely at birth, while the intra-abdominal remains of it give rise 

 in Dart to a solid fibrous cord, the urachus, and in part to the 



T 2 



