THE FCETAL CIRCULATION. 



271 



with the venous blood of the cluctus Cuvieri or precaval 

 sinus (Figs. 215 to 218, Si, S. V, 'DC, D). 



FIG. 215. DIAGRAM OF THE EMBRYONIC VASCCLAR SYSTEM. 



A, A, dorsal aorta ; RA, RA, right and left roots of the aorta, which arise from the 

 branchial vessels, Ab, by means of the collecting trunks (branchial veins), S, /S' 1 ; 

 c, c 1 , the carotid.3 ; Sb, subclavian artery ; KL, gill-clefts ; Si, sinus venosus ; 

 A, atrium ; V, ventricle ; B, bnlbus arteriosns ; Vm, vitelline veins ; Am, 

 vitelline arteries ; Ic, Ic, common iliac arteries ; E, E, external iliac arteries ; 

 All, allantoic (hypogastric) arteries ; Acd, caudal artery ; VC, HC, anterior and 

 posterior cardinal veins ; jS'6 1 , subclavian vein ; D, Cuvierian duct (precaval 

 veins), into which the anterior and posterior cardinals open. 



The ductus Cuvieri, which runs transversely, is formed on either 

 side by the fusion of the anterior and posterior cardinal 

 veins two larsfe vessels which bringf back the blood from the 



