OF THE GREAT ANTERIOR VEINS. 
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cross branch is shorter and wider. The lower part of each primitive jugular, below 
the cross branch, inclines downwards and outwards, lying upon the pericardium. 
The left cardinal vein is still further reduced in size, but no occlusion has yet taken 
place. 
Fig. 8. Embryo, 1 inch and ^ths long. In this embryo, and in embryo fig. 10, most 
part of the left lung has been cut away. The lower part of the left primitive jugu- 
lar, extending from below the cross branch to the junction of the left cardinal vein and 
left canal of Cuvier, is occluded, and a fine opake cord (o) exists in its place. The 
left cardinal vein and left Cuvierian canal now form the left vena azygos, as in the 
adult, the intrapericardial portion of which is seen to cross the left pulmonary vessels, 
and is lodged in a fold of the serous membrane. The cross branch now passes 
obliquely over to the right side, and forms the left innominate vein, which ends in 
the lower part of the right jugular, now the vena cava superior. 
Fig. 9. Back of the heart of an embryo, 1^ inch long, to show the differences, in 
size, length and direction, between the right and left Cuvierian canals, after the partial 
occlusion of the left jugular. The different heights of the right and left azygos veins 
are also exhibited. 
Fig. 10. Embryo, 1^ inch in length ; it shows the state of the primitive anterior 
venous trunks after the completion of their metamorphosis, and therefore resembles 
the adult condition. 
PLATE III. 
Development of the great anterior veins in the human embryo. Each figure is 
magnified two diameters. Corresponding letters of reference are used in all cases, 
viz. a. The right, and a', the left primitive jugular vein. h. The right, and h', the left 
cardinal vein. c. The right, and c', the left canal of Cuvier, or its pervious remnants, 
c". Occluded portion of the left canal of Cuvier, d. The transverse branch in the 
neck, afterwards the left innominate vein. e. The vena cava inferior, h. The vena 
cava superior, i. Trunk of the left superior intercostal vein. 2. Left auricle. 3. Ven- 
tricular portion of the heart. 4. Lung, or part of lung. 5. Wolflfian body. 6. Part of 
the liver. 7- The stomach. 
Figs. 1, 2. Left and right lateral view of an embryo, ^ths of an inch in length. 
The cross branch is fully formed and very wide. The cardinal veins have diminished 
with the wasting of the Wolffian bodies ; but no occlusion having taken place, the 
great lateral venous trunks are still symmetrical. N.B. Embryo damaged before dis- 
section. 
Fig. 3. Embryo, l^ths of an inch long. The lower part of the left primitive jugular 
(below the cross branch) is elongated, and, as well as the left Cuvierian canal, is be- 
ginning to shrink. 
Fig. 4. Embryo, l^ths of an inch long. The left primitive jugular vein below the 
