886 THE VASCULAR SYSTEM. 
of the left innominate veins, the superior vena cava, the azygos veins, the left superior 
intercostal vein, part of the inferior vena cava, the right common ilac vein, a small part of 
the left common iliac vein, and both right and left internal iliac veins. 
The primitive jugular vein of each side returns blood from the head and neck, and 
corresponding upper extremity, and it terminates below by fusing with the cardinal vein 
to form a common trunk, the duct of Cuvier, which opens into the sinus venosus. Each 
cardinal vein returns blood from the 
Cae ee , )—Lateral sinus body wall, the Wolffian body, and the 
Te if lower extremity of its own side. 
| ; : Numerous transverse anastomoses are 
developed between the primitive jugular 
and cardinal veins of opposite sides, and 
~ of these four are specially important, one 
———Subelavian vein between the primitive jugular veins and 
eee Seen anastomosis three between the cardinal veins; the 
| former becomes the left innominate vein ; 
of the latter, the upper two become the 
transverse parts of the upper and lower 
—Heart smaller azygos veins, and the third forms 
the left common iliac vein. As these 
Transverse anastomosis transverse channels develop, further 
changes occur in the primitive jugular 
and cardinal trunks. At first the upper 
extremity of the primitive jugular vein 
is in direct continuity with the venous 
Liver sinuses of the cranium through an 
aperture, the post-condyloid foramen, in 
front of the external ear; but this con- 
tinuity is destroyed, and the aperture in 
the skull closes as soon as a new vessel, 
which becomes the internal jugular vein, 
has grown upwards from a point on the 
inner side of the primitive jugular trunk 
and has established a communication 
with the lateral sinus through the jugular 
foramen. This vessel rises behind the 
Splenic vera sterno-clavicular joint, just opposite to, 
Cardinal vein 
Duct of Cuvier 
Vena revehens 
Vena advehens 
Umbilical vein 
} Superior mesenteric vein or shghtly below, the entrance of the 
vA subclavian vein into the outer side of 
Vitelline vein the primitive jugular vein. 
With the exception of its upper 
extremity, the whole of the primitive 
jugular vein remains on both sides in 
the adult. On the right side, above the 
transverse anastomosis between the two 
primitive jugular veins which becomes 
Se iliac vein the left innominate vein, it forms the 
external jugular vein, and that portion 
\ of the right subclavian vein which inter- 
venes between the external jugular and 
internal jugular veins and also the right 
Stage II].—The right umbilical vein has disappeared, and HLOUeLOLUN TRAE ver below the anaspoU ts 
the superior mesenteric and splenic veins have joined it forms the upper part of the supene 
the fused vitelline veins. vena cava, the lower part of the latter 
vessel from the entrance of the vena 
azygos major downwards representing the right duct of Cuvier, which, though it is placed 
transversely in the early stages, becomes more vertical as the heart descends in the 
thoracic cavity. On the left side above the transverse anastomosis it forms the external 
jugular vein, the innermost part of the subclavian vein, and a small part of the left 
innominate vein; the main part of the latter vessel being formed, as before stated, from 
the transverse anastomosis. The portion of the left primitive jugular vein which lies 
below the anastomosis is represented in the adult by the upper part of the left superior 
intercostal vein. 
r'ransverse anastomosis 
Fic. 605.—DEVELOPMENT OF THE VENOUS SYSTEM 
(Diagrammatic). 
