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. Plato, as Galen informs us, first called it diaphragm, from the verb διαφράσσειν, to separate or be between two. Till his time it had been called φρένη, from a notion that an inflammation of this part produced phrenzy; which is not more warranted by experience than another tradition, that a transverse section of the diaphragm with a sword causes the patient to die laughing.