VI 



VENOUS SYSTKM 



413 



in the body-wall. An inferior jugular vein (i.j) passes back from 

 tin- head-region, lateral to the pericardiac cavity, and opens into the 

 anterior cardinal close to its hind end and on its ventral side. In 

 lain- stages the point <>f junction of the inferior jugular with the 

 anterior cardinal comes to be shifted relatively forwards, as was the 

 case with the subclavian. Farther forwards the anterior cardinal is 

 joined j.y an anterior and a posterior cerebral vein (ce f and ce") from 



a.c.u. 



uu 



y.s.u. 



p.c.v. 



an. 



v.v. 



y.s.u. 



B 



Fi<;. 191. Diagrams illustrating early stages in the development of the venous system 

 of Elasmobranchs according to Rabl (1892) and Hochstetter (1906). 



ii.f.r. anterior cardinal vein ; UH, fused portion of vitellinc veins behind liver ; cl, position of cloaca ; 

 '/.'', duct of Cuvier; A.r, hepatic MMII; /<.<.,-. posterior cardinal vein; s.t.r, snbintcstinal vein; c.r. 

 vitelline vein : t/.*.i\ main vein from yolk sac. 



the inside of the head. At the hind end of the system rectal (r) 

 and pelvic (j)l) veins open into the renal portal. The former appear 

 to be the persistent remains of the anastomotic brandies which in 

 early stages connected the hind end of the subintestinal vein with 

 the posterior cardinal. 



ELASMOBRANCHII. It is instructive to compare with the develop- 

 ment of the venous system in a holoblastic vertebrate the correspond- 

 ing phenomena as they occur in the Elasmobranchs, the lowest of the 

 meroblastic gnathostomes. An inspection of Fig. 191 brings out the 

 most conspicuous difference, one that could be foretold a priori, 



