324 



COMPARATIVE ANATOMY 



Os 



-Cdv 



FIG. 265. DIAGRAM OF STAGES IN THE DEVELOPMENT OF THE VEINS IN ELASMO- 

 ERANCHS. (I XI after Rabl, XII after F. Hochstetter. ) 



Ca, Cp, anterior and posterior cardinal veins ; Cdv, caudal vein ; D,D, vitelline 

 veins ; DC, precaval vein or sinus ; Cl, region of the cloaca ; H, sinus 

 venosus of heart ; J, subintestinal vein ; Jr. V, interrenal vein ; Lb, hepatic 

 veins ; **, hepatic sinus ; Npf, renal portal system ; VP, hepatic portal vein ; 

 Vpo, capillaries of the hepatic portal system ; f, cardinal sinus ; Sbc, sub- 

 clavian vein ; Os, Od, left and right oinphalo-mesenteric veins. 



the precaval sinus or proximal end of the posterior cardinal 

 vein. 



The caudal vein usually bifurcates posteriorly to the cloaca, each 

 branch passing along the outer side of the corresponding kidney, 



