We now proceed to give particulars regarding the properties and
functions of the veins. There are two blood-vessels in the thorax by
the backbone, and lying to its inner side; and of these two the larger
one is situated to the front, and the lesser one is to the rear of it;
and the larger is situated rather to the right hand side of the
body, and the lesser one to the left; and by some this vein is
termed the 'aorta', from the fact that even in dead bodies part of
it is observed to be full of air. These blood-vessels have their
origins in the heart, for they traverse the other viscera, in whatever
direction they happen to run, without in any way losing their
distinctive characteristic as blood-vessels, whereas the heart is as
it were a part of them (and that too more in respect to the
frontward and larger one of the two), owing to the fact that these two
veins are above and below, with the heart lying midway.