OO, 
DIVISION OF THE HEART AND AORTIC BULB. 881 
and it consists of a transverse portion connecting a large right with a small left cornu. 
Gradually the orifice of communication is constricted, and ultimately it is transformed 
into a cleft which opens from the right end of the sinus into the back of the right part 
of the auricular chamber; the cleft is guarded by two lateral valvelike folds of 
endocardium, the right and left venous valves, which become continuous above with 
1st cephalic aortic arch (obliterated) 
‘ Internal carotid artery 
Internal jugular vein - 
2nd cephalic aortic arch (obliterated) 
External jugular vein - 
| ! 
4 ; External carotid 
3rd cephalic aortic arch forming part of 
internal carotid 
;-—— Vertebral artery 
j/—>—Subclavian artery 
<= s—4th cephalic aortic arch forming arch of aorta 
Left superior intercostal vein 
EN Ductus arteriosus (part of the fifth aortic 
; arch) 
<= Pulmonary artery 
(-——>—_Vena azygos minor superior 
——— 
Left auricle 
Vertebral artery — 
Subclavian artery — 
Subclavian vein — 
Innominate veins —— 
Right pulmonary ——\_ 9 
artery 
Superior vena cava _-¥4 
Vena azygos major y 
Right auricle—< tt =—~\ p “\ \ imertnventrele 
Right ventricle Sa tsi 
s L- ; 
Hepatic vein i =A] EL 
Inferior vena cava —— — 
a) Vie 
Intercostal veins 
Vena azygos minor inferior 
rl > == Ductus venosus 
Obliterated portion of the ; Dorsal aorta 
right cardinal vein 
Stem formed by fused 
vitelline veins 
Obliterated left cardinal vein 
GN 
l 
ees vein 
z Umbilical vein 
S » > 
Renal vein | = 
Pie 
- —_— ‘| 
Lumbar vein —-~ , 
Placenta 
" 
ft. Allantoie arteries 
Common iliac artery 
External iliac artery 
Internal iliac artery 
Fic. 602.—DIAGRAM OF THE COURSE OF THE FmTaL CIRCULATION. 
a transitory downward projection from the roof of the auricle, known as the septum 
spurium. 
In the early stages the veins of the two sides opened into the corresponding sections 
of the sinus venosus, but numerous transformations, which are described in the account 
of the development of the veins, occur, and finally all the veins, except the left duct of 
Cuvier, open into the right end of the sinus, which is gradually absorbed into the 
auricular cavity ; the transverse part of the sinus, which becomes a mere appendage of the 
right end, is transformed into the coronary sinus, which receives the blood from the walls 
56 
