THE ANATOMY OF TEN TO TWELVE MM. PIG EMBRYOS 



131 



Of the two subcardinal veins, the right has become very large through its con- 

 nection with the right posterior cardinal vein and the common hepatic vein, and 

 now forms the middle portion of the inferior vena cava. For the development 

 of this vein, see Chapter IX. 



Gen 



Fig. 121 B. — Reconstruction of a 12 mm. pig embryo to show the veins from the left side (Lewis). 

 X 13.5. A., umbilical artery; Ao., aorta; Au., right auricle (atrium); Card.', Card.", superior and in- 

 ferior sections of posterior cardinal vein; d, left common cardinal vein; D.C., right common cardinal 

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

 sinus; mx, transverse vein; P., pulmonary artery; Sc, subcardinal vein; ScL, subclavian vein; Sis., 

 anlage of sup. longitudinal sinus; Um. d., right umbilical vein; Yen., 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. 



The Umbilical Veins (Figs. 121 and 122) anastomose in the umbilical cord, 

 separate on entering the embryo, and course in the ventro-lateral body wall of 

 each side cranially to the ventral lobe of the liver. The left vein is much the 

 larger and, after entering the liver, its course is to the right and dorsad. After 

 connecting with the portal vein, it continues as the ductus venosus and joins the 



