292 



COMPARATIVE MORPHOLOGY OF VERTEBRATES. 



portion of the postcardinals which have joined the anterior ends of the 

 subcardinals (fig. 294, C). The changes in the postcardinals and the 

 renal portal system of mammals will be described below. 



In Ceratodus (dipnoi, fig. 296, A) there are some differences from the above 

 account. Thus the anterior portion of the right postcardinal (not shown in the 

 figure) loses its connexion with the vessels behind and acts as a vertebral vein, 

 taking the blood from the intercostal veins of that side back to the heart. The 





A 



FIG. 296. A, venous system of Ceratodus, dorsal view, after Spencer; B, of a urodele, 

 ventral view, ab, abdominal vein; av, venae advehentes; b, brachial; c, caudal; cd, Cuvierian 

 duct; ej, external jugular; h, heart; hp, hepatic portal; /?', inferior jugular; j, jugular; il, 

 iliac; I, liver; Ic, lateral cutaneus; m, mesonephros; p, postcava; pc, postcardinal; r, venae 

 revehentes; 5, subclavian; t, testes. 



caudal and the subcardinals form a continuous trunk, the revehent vessels forming 

 side branches. The posterior portions of the postcardinals grow back into the 

 tail as paired vessels, forming no connexion with the caudal vein. In Protopterus 

 the vertebral vein is lacking, the subcardinals are not fused behind while the 

 advehent veins are connected with the caudal. 



The development of lungs brings about the appearance of one or 

 more pairs of pulmonary veins which bring the (arterial) blood from 

 these organs to the heart. These arise as an outgrowth from the 



