THE LATER DEVELOPMENT OF THE FROG 



187 



the suspensory fold of the liver (mesohepaticum) to the right 

 posterior cardinal vein, with which it connects, just in front of 

 the beginning of the median cardinal vein (i.e., immediately 



w 



lc 



FIG. 68. The development of the posterior part of the venqus system in the 

 frog. After Shore. A. Portion of a transverse section through the posterior 

 mesonephric region of an 18 mm. tadpole. B. Diagram of the veins of a 25-30 

 mm. tadpole. C. Diagram of the veins of the adult frog, a, Dorsal aorta; c, 

 vena cava; e, nuclei of the endothelial lining of the mesopheric sinus, continuous 

 with the vascular endothelium; /, femoral vein; i, iliac vein; lc, lateral mesone- 

 phric channel of the posterior cardinal vein; m, mesentery; mn, mesonephros; 

 n, mesonephric tubules; p, posterior cardinal veins (in C showing their original 

 location); pv, pelvic vein; rp, renal-portal vein; rr, revehent renal veins; sc, 

 sciatic vein; st, nephrostome; u, caudal vein; vein, median mesonephric channel 

 of the posterior cardinal vein; W, Wolffian duct; x, connection between caudal 

 vein and the lateral mesonephric channels; 1-1, part of the renal-portal vein 

 formed from the lateral channel of the posterior cardinal; 2-2, part of the renal- 

 portal vein formed from the median channel of the posterior cardinal vein. 



posterior to the pronephric region). This new channel en- 

 larges rapidly and ultimately becomes the largest blood vessel 

 . of the body. Through the liver it passes directly to the sinus 



