S4 THE FROC; chap. 



{pt. rv), a wide vessel lying between the kidneys and 

 extending forwards to the liver (Fig. 4). It runs parallel with 

 and beneath; i.e., ventral to, the dorsal aorta (Fig. 5), from 

 which it is at once distinguished by its greater diameter. 

 I'osteriorily it is formed by the confluence of four rej/a/ 

 veins (Fig. 21, rii) from each kidney, and it also receives 

 in the male, spermatic veins (sprn) from the spermaries, and 

 in the female, ovarian veins from the ovaries. Anteriorly 

 it perforates the liver {Ivr), receiving two hepatic veins (Jip) 

 from that organ, and finally enters the sinus venosus. 



We have now to consider a striking want of correspondence 

 between the arterial and venous systems of the frog. As 

 you will remember, the dorsal aorta, after giving off the 

 renal arteries, passes backwards and divides into the two 

 iliac arteries for the legs. You might naturally expect a 

 somewhat similar arrangement with the veins, especially if 

 you have studied human physiology and learnt how the 

 posterior (or inferior) vena ca\a of man is formed by the 

 confluence of the veins from the legs, and receives higher 

 up those from the kidneys. In the frog, as we have just 

 seen, the postcaval does not reach to the hinder boundary 

 of the kidneys, and the renal veins are the only vessels 

 entering its posterior end. 



In the frog, as a matter of fact, the connections of the 

 veins of the legs are very peculiar. You remember the 

 abdominal vein seen in our preliminary dissection (Figs. 2, 

 3 and 4, abd. v). This vessel, if traced backwards, is found 

 to fork at the posterior end of the abdomen — or more accu- 

 ratel)-, the single abdominal vein is found to be formed by 

 the c:onfluence of iwo pelvic veins (Fig. 21, pv), which can be 

 traced along the base of the leg (compare Fig. 3). Towards the 

 front of the thigh is the princii)al vein of the leg, ihe femoral 

 vein{V\g. 21, f.m), which on emerging from the leg, divides 



