396 



COMPARATIVE ANATOMY 



of these has given off branches to the head (carotids), they all unite 

 above the clefts, usually forming a longitudinal trunk on either side: 

 these constitute the right and left roots of the dorsal aorta, which 



Fm. 299. DIAGRAM OF THE EMBRYONIC VASCULAR SYSTEM FROM THE VENTRAL 

 SIDE. (The portal systems are not shown.) 



A, atrium ; A, A, dorsal aorta ; Acd, caudal artery ; All, allantoic (hypogastric) 

 arteries ; Am, vitelline arteries ; B, truncus arteriosus ; c, c 1 , carotids ; 

 D, precaval veins (ductus Cuvieri), E, external iliac artery ; Ic, common 

 iliac ; KL, gill-clefts ; RA, RA, right and left roots of the aorta, which arise 

 from the branchial vessels Ab, by means of the collecting trunks, !?, S l ; 

 >/, subclavian artery ; SI* 1 , subclavian vein; Si, sinus venosus ; V, ventricle; 

 VG, HO, anterior and posterior cardinal veins ; Yin, vitelline veins. 



extends backwards along the ventral side of the vertebral axis 

 into the tail as a large unpaired trunk, giving off numerous 

 branches including paired embryonic mtelline or omphalo- 



