SB' Observations on the Nahwal History 
the blood by the vessels given off from the aorta, it is unneces- 
sary to say more ; but of the return of this blood to the heart 
by the veins, it is proper to take some notice. 
There are three principal veins which reconvey the blood from 
the different parts of the body to the heart ; two corresponding 
to th e jugulars, and the third to the ascending vena cava. The 
two former, after receiving the blood which returns from the 
head, pour it into the cava, where that vein is so dilated as 
to form a sort of sinus. Into the cava, also, at different parts, 
is poured all the blood returned from the trunk. Thus two 
large veins which ascend the spine on each side of the aorta, 
and receive the blood of the dorsal veins in their progress, 
enter the cava much below the middle of the trunk. The blood 
of the air-bladder and organs of generation is poured, by a 
single vein, into the cava about the middle of the kidney. The 
vein which collects the blood from the intestines, arises near the 
termination of the alimentary canal ; and proceeding between the 
expanded portions of the peritonaeum that form the mesentery, 
gains the neighbourhood of the stomach : there its trunk, which 
may be called the vena porta , is spread entirely through the 
concave surface of the liver. After circulating through that 
viscus, the blood is again collected into one vein, which, travers- 
ing the edge of the liver, pours its blood into the cava at the 
point where that vessel itself quits the liver to continue its course 
to the auricle. 
6. Of the Organs of Respiration. 
Ih the preceding chapter on the organs of circulation, the 
authors have described, with all the accuracy they were able, the 
course of the branchial arteries and veins to and from the gills, 
which might be considered as including a description of the res- 
piratory organs ; but as the proteus anguinus , besides being fur- 
nished with gills, is provided also with two air-bladders, which, 
from a resemblance to the lungs of the aquatic salamander, have 
been regarded as two real lungs, it is necessary to give a more 
particular description of those two organs. 
In the bottom of the fauces, and exactly in the middle of 
that space which lies between the branchial apertures which 
communicate with the gills of each side respectively, there is a 
