552 ANATOMY OF VERTEBRATES. 



remnant, recognisable by the developmental anatomist, becomes 

 the ■ coronary sinus ' of Anthropotomy, or the dilated portion of 

 the heart-vein, with well-marked fibrous tunic, receiving the 

 ' oblique auricular vein ' representing the left i ductus Cuvieri,' 

 and terminating by the wide valvular opening in the right 

 auricle. 1 



In the Monotremes each precaval, fig. 308, e,f, receives the 

 azygos vein of its respective side : they are united by the cha- 

 racteristically mammalian transverse canal, g, which becomes the 

 ' vena innominata ' in Man. The postcaval has a long course in 

 the thorax ; before entering which it is greatly dilated, within 

 the liver, in the Ornithorhynchus, as it is in the placental divers. 

 The vena porta? is constituted as in other Mammalia. The veins of 

 the kidney are continued from the renal artery, and communicate 

 solely with the postcaval. In the Marsupials, also, the iliac veins 

 combine to form the postcaval trunk, as in the rest of the Mammalia, 

 without conveying any part of their blood to the kidneys : in the 

 Kangaroo they both pass on the central aspect of the iliac arteries. 

 The renal veins, in like manner, directly communicate with the ab- 

 dominal cava, and do not contribute any share in the formation of 

 the portal vein. This great secerning trunk of the hepatic organ 

 presents the strictly mammalian condition, being formed by the 

 reunion of the gastric, intestinal, pancreatic, and splenic veins. 

 ' The primitive veins of the animal system of organs, commonly 

 called iC azygos," retain their original separation and symmetry; 

 the left " azygos " bends over the left bronchus to communicate 

 with the left precaval, and the right azygos over the right bronchus 

 to join the right precaval.' 2 This vein, b, returns the blood from 

 the right side of the head and the right anterior extremity ; the 

 corresponding vein on the left side, c, passes down in all the 

 Marsupials, in front of the root of the left lung, as in Birds and 

 Reptiles, behind the left auricle, and, after receiving the coronary 

 vein, joins the postcaval, d, immediately before its expansion into 

 the auricle. The anterior anastomosing vein between the two 

 precavals exists. 



Where the pelvic extremities are less or not larger than the 

 pectoral ones, as in the Ursine Dasyure and Wombat, the post- 

 caval is somewhat less than the left precaval, figs. 402 and 403, 

 and they appear to terminate by separate apertures in the auricle ; 

 but in the Kangaroo, fig. 401, the proportions of the two veins are 

 reversed, and the postcaval more obviously receives the left pre- 



1 ccvn". (1848.) 2 lxxx-. (1842) p. 308. 



