1196 



EMBRYOLOGY. 



abdominal wall ; it receives the renal veins from the kidneys, and forms, up to 

 this level, the inferior vena cava. Above the level of the renal veins the inferior 

 vena cava first makes its appearance as a small vein lying in the tissue between 

 the two kidneys. Superiorly it opens into the sinus venosus, while below it com- 



Anterior detached portions 

 of umbilical veins. 



Vense revehentes. 



Stomach. - 



Vense advehentes. - 

 Pancreas. 

 Bile duct. .- 



Obliterated portions' 

 of venous rings. 



Right umbilical vein.. 



-Ductus venosus. 



^* Liver. 



f\Left umbilical vein. 



Duodenum. 



Vitelline \ 

 veins. Portal vein. 



FIG. 754. The liver, and the veins in connection with it, of a human emhryo, twenty-four or twenty-five 

 days old, as seen from the ventral surface. (After His.) (Copied from Milnes Marshall's Embryology.) 



municates with the right cardinal vein near the level of the renal veins (Fig. 755, 

 1, 2). This small vein ultimately becomes enlarged, and carries the blood upward 

 from the right cardinal vein, and so forms the upper part of the inferior vena cava. 

 The portion of the right cardinal vein above the renal veins persists as the vena 



Hal 



FIG. 755. Illustrating the development of the principal systemic veins. (Hertwig.) dc. Duct of Cuyier. 

 'je,ji. External and internal jugular veins, s. Subclavian. vh. Hepatic veins. U. Umbilical, ci, ci 2 . Vena 

 cava inferior, ca (pa 1 , ca 2 , ca 3 ). Cardinal veins. ilcd,ilcs. Right and left common iliac veins, ad, as. Eight and 

 left innominate veins, cs. Vena eava superior, ess. Rudimentary portion of left superior vena cava. cc. Coro- 

 nary sinus, az. Azygos major, hz, hz l . Azygos minor. He. External iliac. Hi. Internal iliac, r. Renal vein. 



azygos major, and receives the right intercostal veins, while the vena azygos minor 

 is brought into communication with it by the development of transverse branches 

 in front of the spinal column (Fig. 755, 2, 3). 



