In the case of the ovipara, such as birds and oviparous
quadrupeds, the two parts of the organ are separated to a distance
from one another, so that the creatures appear to be furnished with
a pair of lungs; and from the windpipe, itself single, there branch
off two separate parts extending to each of the two divisions of the
lung. It is attached also to the great vein and to what is
designated the 'aorta'. When the windpipe is charged with air, the air
passes on to the hollow parts of the lung. These parts have divisions,
composed of gristle, which meet at an acute angle; from the
divisions run passages through the entire lung, giving off smaller and
smaller ramifications. The heart also is attached to the windpipe,
by connexions of fat, gristle, and sinew; and at the point of juncture
there is a hollow.