 Not all animals have a neck, but only those with the parts for the sake of which the neck is naturally present—these are the windpipe and the part known as the esophagus. Now the larynx is present by nature for the sake of breathing; for it is through this part that animals draw in and expel air when they inhale and exhale. This is why those without a lung have no neck, e.g. the kind consisting of the fish. The esophagus is the part through which nourishment proceeds to the gut; so that animals without necks manifestly do not have an esophagus. But it is not necessary to have the esophagus for the sake of nutrition; for it concocts nothing. And further, it is possible for the gut to be placed right next to the position of the mouth, while for the lung this is impossible. For there needs first to be something common like a conduit, which then divides in two and through which the air is separated into passages—in this way the lung may best accomplish inhalation and exhalation.