2QO 



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 



FIG. 294. Relations and modifications of the post- and subcardinal, abdominal and 

 postcaval veins in different stages ot the amphibia. In A the veins (il) from the hind limb 

 return directly to the heart by the lateral abdominal veins (la), 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 (/>), 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 (r). 



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 



