DIAPHRAGM, (Diaphragma), in Anatomy, a part vulgarly called the midriff, and by anatomists septum transversum. It is a strong muscular substance, separating the breast or thorax from the abdomen or lower venter, and serving as a partition between the abdominal and the thoracic viscera. See ANATOMY INDEX.
It was Plato, as Galen informs us, who first called it diaphragm, from the verb διαφραγμα, to separate or be between two. Till his time it had been called phrene, from a notion that an inflammation of this part produced phrenzy; which is not at all warranted by experience, any more than that other tradition, that a transverse section of the diaphragm with a sword causes the patient to die laughing.