290 COMPARATIVE MORPHOLOGY OF VERTEBRATES. 
In the fishes the vessels of the appendages are but slightly developed, 
there being a subclavian vein entering the Cuvierian duct, and occa- 
sionally a brachial vein which may empty into the sinus venosus. In 
the amphibia a cutaneus magnus vein (fig. 302), coming from the 
skin of the trunk, may enter the subclavian, while in all tetrapoda the 
subclavian, after leaving the limb, receives a superficial cephalic and an 
axillary vein, the latter changing its name in the appendage to the 
Fic. 294.—Relations and modifications of the post- and subcardinal, abdominal and 
postcaval veins in different stages ot the amphibia. In A the veins (i) from the hind limb 
return directly to the heart by the lateral abdominal veins (72), while the blood from the 
tail (c) passes by way of the subcardinals (sc) through the mesonephroi to the postcardinals 
(pc). In B the lateral abdominals have united in front to form the anterior abdominal 
vein (aa); the iliacs have sent a branch to the postcardinals, which have grown back to join 
the caudals, while the subcardinals have lost their connexion with the caudal and have 
acquired one with the postcava (p), a backward growth from the sinus venosus. In C the 
postcardinals have been interrupted, the posterior half of each now forming an advehent 
vein while the subcardinals, as in B, form the revehent veins (7). 
brachial vein. In the hind limb the common iliac vein is formed by 
the union of the femoral and sciatic (ischiadic) veins, as well as the 
hypogastric (internal iliac) vein already referred to. 
In the classes above fishes (dipnoi, amphibia and amniotes) a new 
vein, the postcava (vena cava inferior) appears. This arises in 
part from scattered spaces, in part as a diverticulum of the sinus 
venosus and the hepatic veins, and grows backward, dorsal to the liver, 
until it meets and fuses with the right subcardinal vein (fig. 295), a 
