The great blood-vessel, then, is attached to the biggest of the
three chambers, the one that lies uppermost and on the right-hand
side; it then extends right through the chamber, coming out as
blood-vessel again; just as though the cavity of the heart were a part
of the vessel, in which the blood broadens its channel as a river that
widens out in a lake. The aorta is attached to the middle chamber;
only, by the way, it is connected with it by much narrower pipe.

The great blood-vessel then passes through the heart (and runs
from the heart into the aorta). The great vessel looks as though
made of membrane or skin, while the aorta is narrower than it, and
is very sinewy; and as it stretches away to the head and to the
lower parts it becomes exceedingly narrow and sinewy.