DEVELOPMENT OF THE VEINS 



28l 



internal iliac vein from the posterior extremities, mesonephric branches from the 

 mid-kidney and dorsal segmental veins from the body wall (Fig. 2 74, B) . Median 



B 



Fig. 275. — Veins of the head, A, in a 9 mm. human embryo; B, in an n mm. embryo (Mall). 



and ventral to the mesonephros are developed the subcardinal veins which are 

 connected at intervals with the posterior cardinal veins by sinusoids and with 

 each other by anastomoses ventral to the aorta. Thus all the blood from the 



