THE ANATOMY OF TEN TO TWELVE MM. PIG EMBRYOS 



123 



The umbilical arteries now arise laterally from secondary trunks which 

 persist as the common iliac arteries. 



The Veins. — The cardinal veins have been reconstructed by Lewis in a 12 

 mm. pig (Fig. 126). The veins of the head drain into the anterior cardinal vein, 



■com. 

 card.' 



Gen. 



Fig. 126 B. — Reconstruction of a 12 mm. pig embryo to show the veins from the left side (Lewis). 

 X 9. A., Umbilical artery; Ao., aorta; Au., right auricle (atrium); card.', card.", superior and in- 

 ferior sectionsof posterior cardinal vein; d,\eit common cardinal vein; D.C., right common cardinal 

 vein; D.V., ductus venosus; Jug.', Jug.", jugular or ant. cardinal vein; L., liver; Z-.o., anlage of lateral 

 sinus; mx, transverse vein; P., pulmonary artery; Sc, subcardinal vein; 5c/., subclavian vein; sis., 

 anlage of sup. longitudinal sinus; Um.d., right umbilical vein; Ven., right ventricle; V.H.C., common 

 hepatic vein; V.op., ophthalmic vein; V.P., portal vein; X, anastomosis between the right and left 

 subcardinal veins. 



which becomes the internal jugular vein of the adult. After receiving the ex- 

 ternal jugular veins and the subclavian veins from the upper limb buds the anterior 

 cardinals open into the common cardinal veins (duct of Cuvier) . 



The posterior cardinal veins arise in the caudal region, course dorsal to the 

 mesonephroi, and drain the mesonephric sinusoids. The subcardinal veins 



