Whitney^ on the Circulation in the Tadpole. 7 
We have already traced the lower vena cava to the sinus 
venosus. Let us now return to the head,, w^here we left the 
cephalic arteries to supply the brain^ lips^ &c. The circula- 
tion in the fringed lips forms a most complicated network of 
vessels, out of which proceeds a vein corresponding to the 
artery already traced. This descends in a direct course till 
it joins the principal vein of the head, which corresponds to 
our own jugular. This latter, formed by the union of smaller 
ones converging to it from all parts of the head, descends in 
front of the large transverse muscles, passes downwards in 
front of the lung close to its inner edge, and continuing to 
descend in a direct course, seems to be making its way into 
the abdomen. But the abstinent system, by removing the 
screen of loaded bowel, revealed the subsequent course of 
this vessel. The vein, having reached the lower edge of the 
lung and arrived at the very margin of the abdomen, 
turns suddenly at a right angle and runs straight to the 
sinus venosus. We observe that at the point of the 
angle this A^ein receives into it the current of another large 
one, running upwards from the abdomen to meet it. Herein 
is the probable explanation of this eccentric course (figs. 
2, 3, letter t). The union of this jugular vein from above 
with the abdominal vein from below forms the upper vena 
cava. We have two more large abdominal veins, which meet 
close together, and pour their blood into the sinus atuosus, 
between the lower vena cava on one side and the upper vena 
on the other (u). We have detected distinctly on the 
right side a venous trunk, returning blood from the lung, and 
emptying itself into the auricle or sinus (v). This is the 
pulmonary vein, bringing the aerated blood from the lung to 
the heart ; but observe that the proportion of aerated blood 
thus contributed is very small compared with the quantity of 
venous blood poured into the same cavity at the same moment 
from i\\Qfive other sources I have described. There is doubt- 
less a left pulmonary vein, corresponding to the one on the 
right side, but as we have not yet been fortunate enough to 
see it, I have not figured it. 
Thus we have traced the blood through its main channels 
and completed the circle of its course. But the special point 
in relation to the anatomy and physiology of the tadpole, as 
a creature distinct from the fish on one hand and the reptile 
on the other, yet remains to be mentioned. The three large 
arteries which arise from the heart become (according to the 
evidence we have obtained, the cephalic, pulmonary, and aortic 
trunks. Herein we dififer from the received view of these 
arterial arrangements. The first trunk, according to Dr. Car- 
