THE DEVELOPMENT OF THE VASCULAR SYSTEM. 85 



the JiepatiG vein (yA), carrying the hepatic blood to the in- 

 ferior cava, and thence to the heart. 



The umbilical vein further gives a branch to the liver ; 

 while, on the other hand, it communicates directly with the 

 venous sinus (now almost merged in the vena cava inferior) 

 by a trunk called ductus venosus (Fig. 26, Du). 



Fic 26.— Diaqrram of the arrangement of the principal vessels in a human foetus. — IT, th< 

 heart ; TA, the aortic trunk or cardiac aorta ; c, the common carotid ; c', the external 

 carotid ; g'\ the internal carotid ; s, subclavian ; v, vertebral artery ; 1, 2, 3, 4, 5, th8 

 aortic arches — the persistent Ze/Y aortic arch is hidden. A\ subvertebral aorta; o, om- 

 phalomeseraic artery, going to the umbihcal vesicle -y, with its vitelliae duct dv ; o, om- 

 phalomeseraic vein ; V2}, the vena portas ; L, the liver ; im, the hypogastric or umbilical 

 arteries, with their placental ramifications, m" v/' ; w', the umbihcal vein ; Z>», the ductus 

 venosus; -^/i. tiie hepatic vein ; cy, the vena cava inferior ; t'iZ. the ihac veins ; as, a vena 

 azj^gos ; vc', a vena cardinalis posterior; Z>(7, a ductus Citvieri; the anterior cardinal 

 vein is seen commencing in the head and running down to the ductus Cuvieri on the 

 under side of the numbers 1, 2, 3, 4, 5 ; P, the lungs. 



When the umbilical vesicle and allantois cease to have any 

 further import, as at birth, or before, the omphalomeseraic ar- 

 teries have become intestinal arteries, and the omphalomeseraic 

 vein, the vena portoe. The hypogastric arteries are obliter- 

 ated, except so much of them as is converted into the common 

 iliac arteries. The umbilical vein, or veins, also disappear, or 

 are represented by mere ligaments. 



