posterior vena cava 



adrenal glands 

 renal vein 



kidney. 



spermatic vein 

 ureter, 



left postcardlnal 



external iliac plexus 



" > 



hypogastric plexus-^ / 



middle sacral 



TACHYGLOSSUS 



B 



BRADYPUS 



Figure 1 1-37. The adult renal circulation in specimens of Tochyg/ossus 



and the sloth, Broc^ypus. (After von Gelderen, 1 933) 



of the blood flow involving use of the posterior cardinal 

 channel as a renal portal vein and appearance of a new 

 drainage, the subcardinal, lying in the medioventral part 

 of each kidney. Supracardinals may also appear in the dor- 

 somedial part of the kidney. 



The result of these new channels is that blood return in- 

 volves cross flow through the sinuses of the kidney from pos- 

 terior cardinal to subcardinal. From the latter the blood 

 passes down through the mesentery to reach the heart by a 

 new channel, the postcaval stem. The development of 

 this new channel short circuits the blood which normally 

 returns through the posterior and common cardinals to the 

 heart. 



Loss of most of the mesonephric mass and development 

 and movement of the metanephros results in a new type of 

 circulation for the kidney: arterial from the aorta, and ve- 

 nous into the posterior vena cava. The postcava now extends 

 back, by way of the right supracardinal and postcardinal 

 channels, to the hind limbs, where it receives the common 

 iliac and middle sacral veins. In the monotremes both cardi- 

 nal channels are retained, with anastomoses above the dorsal 

 aorta (Figure 11-37). In the sloth a pair of reticulate channels 

 lies in the position of the paired cardinals of the monotreme. 

 treme. 



The anterior ends of the posterior cardinal channels re- 

 main as the highly variable azygous vessels. That of the 

 right side connects with the anterior or superior vena cava 

 to drain into the heart, and that of the left side has a cross 

 connection with the right. The left vessel is called the hemi- 

 azygous. The left duct of Cuvier forms the coronary sinus of 

 the heart. 



Reptiles In the reptile the same general picture is observed. 

 In Lacerta the postcardinal stems appear first and later sub- 

 cardinal vessels develop. As development continues, the an- 



terior and posterior segments of the postcardinals become 

 separated. The renal portal portion lies on the middle of 

 the undersurface of the kidney and its blood flows into the 

 renal sinuses. From the sinuses the blood is collected into 

 the medial subcardinal channels, which more anteriorly 

 drain into the anterior parts of the postcardinals. 



The changes in this area were described somewhat differ- 

 ently by Hochstetter (1893). The subcardinals at first carry 

 the blood from the caudal vein forward, and the flow through 

 the kidney is toward the postcardinal channels. Later, flow 

 from the caudal vein shifts into the "renal portal" part of 

 the postcardinal, and the blood moves medially through the 

 kidney to the subcardinal channel, which now connects by 

 way of the postcaval stem with the sinus venosus. This same 

 history is also observed in the shark. 



The postcaval stem of the reptile extends down from the 

 right subcardinal, anterior to the gonads, through the mes- 

 entery to the sinus venosus. This channel does away with 

 the flow through the postcardinals anterior to the kidney. 



The posterior part of the postcardinals, the renal portal 

 vessels, also drain into a ventral abdominal vein passing for- 

 ward on the inner surface of the body wall. This vessel an- 

 teriorly enters the liver and feeds directly into the hepatic 

 portal system, as in Sphenodon. 



In the crocodile the posterior vena cava extends back be- 

 tween the kidneys, from which it receives branches, and is 

 joined by the ischiac, caudal, and inferior mesenteric veins. 

 The midline stem continues posteriorly beyond these as 

 the vertebral sinus. The posterior cardinals remain as renal 

 portals leading into the kidney tissues. There is a pair of 

 ventral abdominal veins partly draining the caudal, ischiac, 

 and femoral stems into the liver. The ventral abdominal 

 arises in the embryo as paired channels in all reptiles. 



In the bird the iliac (the ischiac in some) stem drains the 

 leg into a renal portal channel which connects with hypo- 

 gastric and caudal veins (Figure 11-38). The caudal has a 

 coccygeomesenteric branch which brings blood into the 

 renal portal system from the gut. Although there is direct 

 connection between the renal portal and postcaval stems, 

 valves direct the blood into afferent renal channels. Paral- 

 lel efferent vessels collect it from the kidney tissue. The 

 postcaval stem extends back to the subcardinal anastomosis. 

 The development of the venous channels in birds is like 

 that of the reptiles. The postcardinal channel appears be- 

 fore the subcardinal (see sections of the 72-hr chick). 



The hepatic portal channels of birds and reptiles are 

 similar to those of the mammal. 



Amphibians In the amphibian the posterior ends of the 

 postcardinals function as renal portal vessels connecting 

 with the caudal vein and the ventral abdominal vein. The 

 iliac vein also enters the renal portal vessel of the same 

 side. The ventral abdominal vessel connects with the hepatic 

 portal system. Subcardinal vessels collect from the kidney 

 and lead into the azygous portions of the postcardinals and 



CIRCULATION IN THE BODY 



369 



