THE FROG 17 



cloaca on one side and find the openings of the bladder and the 

 urogenital ducts. 



Sketch the urogenital organs of the female. 



Returning to the injected male, tip the liver forward so that 

 its dorsal surface may be seen. See proceeding from each lobe 

 of the liver an hepatic vein which enters a large venous trunk, 

 the postcava, the anterior portion of which will be traced later. 

 At present follow it backwards. To which side of the oesophagus 

 does it pass? Note the vessels it receives from the fat body, 

 genitalia, and mesonephroi. How far back of the latter organs 

 does it extend? 



On the lateral dorsal surface of each mesonephros is a vessel 

 (Jacobson's vein) which, behind the organ, is called the common 

 iliac vein. Trace it backwards to its origin by the union of two 

 vessels, an external iliac vein, coming from the more ventral 

 part of the leg, and an ischiadic vein, entering the pelvis dorsal to 

 the hip-joint. Which of these veins is connected with the femoral 

 vein (p. 13)? Follow both into the leg. 



Add these vessels to the sketch of the venous system. 



Part of the blood coming from the hind limb finds its way to the 

 heart, by passing, via the common iliac and the postcava, through the 

 kidney. This forms the renal portal system. Another portion passes, 

 by way of the femoral and abdominal vein, through the liver, and hence 

 this forms a part of the hepatic portal system, the rest of which has 

 already been seen. 



The dorsal aorta lies just dorsal to the postcava. In front it 

 can be seen to arise from the union of two arterial trunks, the 

 radices aortae, the rest of which will be followed later. Trace the 

 aorta backwards from this point, noting the origin of the various 

 arteries already seen to arise from it. From what does the com- 

 mon intestinal artery arise? Are the urogenital arteries single 

 or paired in origin? 



Behind the last urogenital artery the aorta gives off a median 

 posterior mesenteric artery which supplies the posterior part of 

 the rectum. Just behind this point it divides into a pair of 

 common iliac arteries, each of which soon gives off an epigastric 

 artery supplying the urinary bladder and ventral body wall. 

 Each common iliac now divides into a femoral and an ischiadic 



