THE VEINS. 



131 



portion of veins above these vascular rings loses its connection with the sinus, 

 while the portion between them breaks up into a capillary plexus, which ramifies 

 in the now partially developed liver together with capillary vessels from the upper 

 venous ring. Of these latter, some pass toward the heart and join the sinus. 

 They have received the name of the vence kepaticce revehentes, and eventually 

 become the hepatic veins ; others ramify in the liver, under the name of vence 

 hepaticce <i<lr t /,, ntes, and become the branches of the portal vein. The lower 

 vascular rino- receives veins from the stomach and intestines, and becomes the 



o 



commencement of the portal vein. 



The umbilical veins at first open into the sinus venosus near to the vitelline 

 veins. Subsequently this communication becomes interrupted by the develop- 



FIG. 100. Diagrams illustrating the development of the great veins. The first figure shows the cardinal 

 veins emptying into the heart by two lateral trunks, " the ducts of Cuvier." The second figure shows the forma- 

 tion of the Venae cavse and the union of the left iliac with the right cardinal, o. Inferior vena cava. b. Left in- 

 nominate vein. The third figure shows the cardinal veins much diminished in size and the duct of Cuvier, on 

 the left side, gradually diminishing, c. Vena azygos minor. The fourth figure shows the adult condition of the 

 venous system. 1. Right auricle of heart. 2. Vena cava superior. 3. Jugular veins. 4. Subclavian veins. 

 5. Vena cava inferior. 6. Iliac veins. 7. Lumbar veins. 8. Vena azygos major. 9. Vena azygos minor. 10. Su- 

 perior intercostal vein. 11. Coronary sinus, the remains of the left duct of Cuvier. (Modified from Dalton.) 



ment of a vascular network ; the vein on the right side atrophies and disappears, 

 while that on the left side greatly enlarges, as the placenta! circulation becomes 

 established, and communicates with the upper venous circle of the vitelline cir- 

 culation. Finally a branch is formed between the upper venous circle and the 

 right hepatic veins, which becomes the ductus venosus, and by it most of the blood 

 from the umbilical vein is carried direct to the heart. 



The Parietal Veins. The first appearance of a parietal system consists in the 

 appearance of two short transverse veins (the ducts of Cuvier), which open on 

 either side of the auricular portion of the heart. Each of these ducts is formed 

 by an ascending and descending vein. The ascending veins return the blood from 

 the parietes of the trunk and the Wolffian bodies, and are called cardinal veins. 

 The two descending ones return the blood (Fig. 100) from the head, and are 

 called primitii.'? jic/ufar veins. The cardinal veins receive the blood returning 

 from the lower limb through the iliac veins. At first the right and left iliac veins 

 open into the corresponding cardinals, but later a connecting vein forms between the 

 lower portions of the cardinals, and through this the blood of the left iliac flows over 

 to join the right cardinal. At the same time a large venous trunk, which receives 

 the blood from the kidneys, forms along the middle line of the posterior abdom- 

 inal wall and unites below with the right cardinal and above with the common 

 trunk of the vitelline and umbilical veins above the point of entrance of the 

 venae revehentes. This is the inferior vena cava. A portion of the right cardi- 



