In viviparous animals, however, the duplication is not so
plainly discernible as in other species, and the duplication is
least discernible in man. And in man the organ is not split into
many parts, as is the case with some vivipara, neither is it smooth,
but its surface is uneven.
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. When the windpipe is charged with air, the entrance
of the air into the heart, though imperceptible in some animals, is
perceptible enough in the larger ones.
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