84 THE FROG CHAP. 



the head and part of the skin and muscles of the 

 abdomen. 



With the posterior end of the sinus venosus is con- 

 nected a single large vein, the postcaval or vena cava 

 Posterior (pt. cv], 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. Posteriorly it is formed by the 

 confluence of four renal veins (Fig. 21, rn) from each 

 kidney, and it also receives, in the male, spermatic veins 

 (spm) from the spermaries, and in the female, ovarian 

 veins from the ovaries. Anteriorly it perforates the 

 liver (Ivr), receiving two hepatic veins (hp) from that 

 organ, and finally enters the sinus venosus. 



We have now to consider a striking want of corre- 

 spondence 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 cava 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 

 it posteriorly. 



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 back- 

 wards, is found to fork at the posterior end of the 

 abdomen or more accurately, the single abdominal 



