THE DEVELOPMENT OF THE VASCULAR SYSTEM. 



8a 



the hepatic vein (vh), 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. 36, 1}v). 



Fio. 26, — Diagram of the arrangement of tlie principal vessels in a human fo3tus. — IT, th* 

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

 carotid ; c", the internal carotid ; fi, subclavian ; -y, vertebral artery ; i, 2, 3, 4, 5, the 

 aortic arches — the persistent left aortic arch is hidden. A\ BUbvertebral aorta ; o, om- 

 phalomeseraic artery, going to the umbilical vesicle i), with its vitelline duct dv ; o, om- 

 phalomeseraic vein \ i)p^ the vena portjB ; L, the liver ; ««, tho hypogastric or umbilical 

 arteries, with their placental ramifications, m" «" ; i^, the umbihcal vein ; i>y, the ductus 

 venosus ; vK tbe hepatic vein ; cv, the vena cava inferior ; 'ffil, the iliac veins ; az, a vena 

 azygos ; vc', a vena cardinalis posterior ; DC^ a ductus Cuvieri ; the anterior cardinal 

 vein is seen commencing in the head and running down to the ductus Ouvieri 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 portse. 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, oi 

 are represented by mere ligaments. 



