a i 
PRIMITIVE VASCULAR SYSTEM AND FCTAL CIRCULATION. 61 
neck, upper extremities, and the thoracic walls; passing from the auricle by the 
right auriculo-ventricular opening it enters the right ventricle; from the right 
ventricle it is forced into the pulmonary artery, and a small part of it traverses the 
lungs and returns to the left auricle by the pulmonary veins; the main part, how- 
Ist cephalic 
aortic arch 
+_—Internal carotid artery 
Internal jugular vein 
2nd cephalie 
External jugular vein aortic arch 
External carotid artery 
3rd cephalic 
aortic arch 
Vertebral artery 
>—Subclavian artery 
<= 4th cephalic aortic arch 
Superior intercostal vein 
Right vertebral artery 
Right subclavian artery 
Right subclavian vein 
, : 5th cephalic aortic arch 
) Innominate veins Pul fae 
ulmonary arte 
4 Pulmonary artery : . 
y ; Vena azygos minor superior 
Superior vena cava Left auricle 
Vena azygos major 
: Right auricle Left ventricle 
Right ventricle 
Hepatic vein 
Inferior vena cava Vena azygos minor inferior 
Intercostal veins Duetus venosus 
Aorta 
Atrophied cardinal vein 
Atrophied cardinal vein 
aT Renal vein 
Umbilical vein 
Portal vein 
Renal vein 
Lumbar vein Placenta 
Common iliac artery 
External iliac artery 
Internal iliac artery 
w ¥ 
y 
, 
a - 
tear 
Middle sacral vein 
Fic, 47.—DIAGRAM OF THE Fa@TaL CIRCULATION. 
ever, is conducted by the ductus arteriosus into the aorta at a point beyond where 
the main vessel of supply to the left upper extremity, the left subclavian artery, 
rises. 
The blood which enters the right auricle by the inferior vena cava is mixed ; it 
consists partly of purified blood from the placenta, and partly of impure blood 
returning from the abdomen and lower extremities. The blood from the placenta 
is returned to the embryo by the umbilical vein. From the umbilical vein it passes 
along a channel called the ductus venosus, which terminates in the upper part of the 
